Is there a far away probe that has recorded the light spectrum from Earth as if it were an exoplanet? We analyze the light spectrum of stars and distant planets to know characteristics like: chemical composition, temperature, mass, etc.

Starting from the same principle, a probe at the border of the solar system could analyze the spectrum of the light reflected by the Earth. In theory, comparing the spectra captured by the probe with what was happening here on Earth at a time, the light was reflected to the space we could discover new spectrographic patterns that would help us look for planets similar to Earth and maybe even life.

I wonder if any study like this has been done, where a whole-Earth spectrum from a distant spacecraft has been captured and analyzed, with the intent of working the problem as if it were a spectrum from an exoplanet, in order to correlate with known Earth conditions.

TL;DR: (1) we don't need to go very far to measure the spectrum of Earth's reflected light: a satellite in orbit around the Earth could easily do that; however, (2) detecting the reflected light of an Earth-size planet is extremely difficult: we currently use other techniques with much greater success.

The Wikipedia article on how scientists detect exoplanets provides a good introduction and overview - well worth a quick read. In summary:

Most of the thousands of exoplanets detected so far have been found using the transit photometry method, where the measured brightness of the star temporarily dips because a planet is blocking some of the light as it transits across the face of the star.

The next most successful technique is to measure changes in the radial velocity of the star to deduce the presence of a planet (by the "wobble" its gravity causes). This was the most productive method until 2012, after which transit photometry became the dominant detection method.

However, neither of these methods are looking for reflected light from the planet.

It is possible to deduce the presence of a planet from periodic changes to a star's brightness that would correspond with a nearby planet going through its phases (like how the Moon is bright when full and "dark" when new), but we're typically talking about a Jupiter-sized exoplanet in a close orbit - definitely not a relatively "tiny" Earth-like planet further out from the star.

It's also possible to directly detect the reflected light, or the infrared light emitted by a "hot" planet, or light that has been polarised by the planet's atmosphere – but all these methods rely on a much-bigger-than-Jupiter planet orbiting a relatively small/dim star, and preferably in our local stellar neighbourhood, since the light we're trying to detect is exceedingly faint. Note that currently the smallest directly-imaged exoplanet is still more massive than Jupiter, and Jupiter itself is over 300 times more massive than the Earth (and ten times the Earth's radius, which is even more relevant).

Note also that Proxima b (an Earth-size planet orbiting our very closest neighbour, the red dwarf Proxima Centauri) was discovered using the radial velocity method, and while efforts are under way to observe it directly, no direct image has yet been obtained. This might give you an indication of just how hard it is to directly image such a (relatively) tiny planet!

Also, we don't need to send a probe to the edge of the solar system to work out what we're looking for, as we already know exactly what the reflected light from Earth looks like – the iconic Earthrise being the most famous example. And in 1990 Voyager 1 took a famous photo of the Earth from 6 billion kilometres (41 AU) away: see the Pale Blue Dot.

By Sept 2017, Voyager 1 was 21 billion km (140 AU) from the Sun - by far the most distant probe we've ever sent. Nonetheless, that's a long way from the "border of the solar system". Voyager has entered the interstellar medium but it hasn't yet left the Kuiper Belt, and it will be another 300 years before it reaches the Oort Cloud, and tens of thousands of years before it reaches the real edge of the Solar System.


What's the name of the point where you are closest or furthest from the ecliptic? Every 24 hour day, there is a point as the earth rotates about its axis, where a location on earth is the closest to the ecliptic and where it's the furthest. Do those two points have a name?

What I mean is on the plane of the ecliptic, as the earth rotates around its axis, a point on the earth at 45 deg north is going to hit a low-point perpendicular to that plane, and will hit a high point perpendicular to that plane.

I don't know of a standard term for that quantity, but I'd call it the ecliptic latitude of the zenith.
With north positive and south negative, this would reach a minimum at 6:00 and a maximum at 18:00 local sidereal time.
These correspond to local solar noon or midnight at the solstices and occur 2 hours earlier per month.

The vectors perpendicular to the ecliptic are called the ecliptic poles. The zenith only coincides with one of these on the Arctic or Antarctic circle, at sunrise (winter-spring) or sunset (summer-fall).


What happens if two galaxies collide very quickly? What would happen if two galaxies collided very quickly (e.g. at near the speed of light)?  Would they mostly just pass through eachother unscathed, or would there be very energetic collisions that would rip both galaxies apart, or would something else happen?

Have 2 people stand in opposite corners of a large empty room each with a jar of marbles.  Have them roll these at each other all at once as fast as they can, and you will get a pretty good answer to your question.

97% (or thereabouts) of a given galaxy is empty space.  Most of one is going to pass harmlessly through the other, though you are likely to get a few collisions.  At or near the speed of light, gravity will have very little effect as well, so a few orbits will be perturbed, but any given star will hardly notice.

I suspect (though I haven't the expertise to say definitively) that the radiation increase during the ~100,000 years or more that this collision would take (assuming the galaxies were of approximately the size of the Milky Way and that they hit exactly edge on) would be significant to any creatures living in your galaxies.

If by the off chance (I'm talking about lightning-striking-a-shark-currently-eating-a-recent-lottery-winner kind of chance) the supermassive black holes at the center of these two galaxies collided, the speed would be no obstacle, and they would combine.  The angular momentum would certainly rip the new black hole from one of, or likely both, of the colliding galaxies.  This would be bad for them.  I propose sending this as a "What If?" question to XKCD.  He seems to have the time to do the math on questions of this nature and follow as far as it leads.


360 degree equirectangular projection of all naked eye stars with precessional motion for simulating For many years now I've been using Voyager sky simulator by Carinasoft. The projection selections are great, but Equirectangular doesn't seem to one one of them. Is there a program out there that does this? I cooked up an Excel sheet to do the coordinate conversions, and I can import these into Autocad if I have to, but it seems like there should be an off-the-shelf package to do this.

For my current project I need to be able to show a 360 degree overview of changes due to precession from 3000-2000-1000 BC at a glance.  It may be my familiarity with the typical simple projection published for surveyors in a standard Ephemeris before the internet and GPS all but eliminated the demand for such publications.

The "cylinder" projection of Stellarium does this:


What percentage of gas giant exoplanets are in the habitable zone? Approximately what percent of exoplanet gas giants discovered so far are in the habitable zones of their stars? I hear that most of them are "Hot Jupiters", orbiting so close to their stars that the heat causes them to swell up like a hot air balloon.

Of the gas giants, the number of "hot Jupiters" is about the same as the number of "hot Neptunes." A little under 9% of known gas giants are in the habitable zones.

An article by John Wenz has the discoveries thus far collated into a chart:

The claim, "most of them are "Hot Jupiters", orbiting so close to their stars that the heat causes them to swell up like a hot air balloon," is at best a bit of a stretch - the only reference that I found for this was a Gizmodo article about Kelt-9b. The Nature paper, A giant planet undergoing extreme ultraviolet irradiation by its hot massive-star host, that discusses Kelt-9b says,

  The planet is also extremely inflated relative to theoretical models, with a radius of $\sim 1.9\ R_J$. Poor redistribution of
  heat and radius inflation (both of which are also observed in WASP-33b), have been linked to high stellar insolation, although the exact physical mechanisms remain uncertain.

So they did observe that Kelt-9b had a larger radius than is normally expected from a planet of that mass, and it receives massive amounts of radiation from its star, but it cannot be concluded from that that it is the same as putting a balloon filled with air near a heat source.


What is the smallest possible planet with same sea level atmospheric pressure as Earth? Suppose there is a planet made of pure tungsten (a quite common and heavy element), with perfect spherical shape.

Which should be its radius so that the air pressure and ground/sea level is the same as on earth ?

I don't know if it is sufficient to have a 1G gravity, because the smaller radius could affect the density of the atmosphere as the gravity will decrease differently that from earth.

For sake of simplificy, say that this planet is on the same orbit as Earth, orbiting around a twin of our Sun. Also magnetic field and atmosphere composition should be comparable to the Earth's one (altough this is not realistic, due to the lack of body of waters).

In the textbook treatment the pressure decreases exponentially with height as $P(z)=P(0)\exp(-z/H)$ where $H=kT/mg$ is the scale height of the atmosphere. This assumes that the gravity $g$ is constant with altitude, which is a decent approximation for planets with an atmospheric height much smaller than their radius. Since $H$ is about 8 km for Earth, this makes sense to use.

For an atmosphere with Earth-like temperature $T$ and mean molecular mass $m$ it would hence seem that for the tungsten planet that if we want $P(0)$ to be like on Earth $g$ must be equal to Earth's 9.82 m/s$^2$. So if we have a planet with $g=G\rho (4\pi r^3/3)/r^2$, we get $r=3g/4\pi G\rho$. For $\rho=19300$ kg/m$^3$ this gives $r=1820$ km.

The limit is met somewhere before white dwarf density. They have a density of about a billion kg/m$^3$ and a 35 meter radius white dwarf would have terrestrial surface gravity. At this point the above approximation has broken down (the scale height is bigger than the radius), and besides the low gravity would not be enough to hold it together. The real determinant of the limit will be the highest density material you can get that is stable at (near) zero pressure. For molecular matter tungsten is likely close to the limit, and we have reason to doubt degenerate white dwarf matter is up to the job.

Note that small but less dense bodies can have quite dense atmospheres. Titan has radius about 2550 km and a surface pressure 1.48 times Earth, despite lower surface gravity. The trick here is that the atmosphere is colder and slightly denser.


Can I see Jupiter, Saturn, Mars and Venus with the Spectra Optics Telescope 600x50? Is it possible to see Jupiter, Saturn, Mars and Venus with the Spectra Optics Telescope 600x50? And even the moon?
This is the description of the telescope:

User-friendly and easy to install with magnification up to 100x.
A telescope is a learning and discovery tool that is suitable for both old and young. This model is larger and has significantly better optics than the telescope that Galileo Galilei used during his astronomical discoveries hundreds of years ago. Magnifies from 30-100x. The viewfinder binoculars (5x24 mm) make it easy to roughly calibrate the telescope and the stand is easy to mount. Focal length 600 mm. Light opening 50 mm. Weight about 3.1 kg. Live incl. 2 eyepieces.**

Generally speaking, you should never buy any telescope which advertises itself in terms of magnification.
Telescopes at this level are, unfortunately, not much more than toys which will serve more to frustrate than to delight.
These telescopes are made almost exclusively from plastic parts - the optical tube, the focuser, even the eyepieces are a polymer and not a glass. The tripods are flimsy aluminium.

If you only have €50 to spend then you could buy a pair of 8x42 or 10x50 binoculars. At this price they won't be a great pair of binoculars, but they'll show you a lot of objects in the night sky which you can't see with the naked eye alone.
More positive points in favour of binoculars:

you can use them during the day
they're very portable
they'll continue to be useful as you continue in the hobby --- I still use my €40 10x50s to sweep the sky even though I have a reflector and a refractor; each instrument gives a different view

Alternatively, you could put that €50 into a savings account and then try to add to it at every opportunity you get. Your goal would be to save up around €200
A telescope which is generally accepted as being one of the best starter telescopes is a 130mm F5 reflector sold in the USA under the name "Astronomers Without Borders OneSky" and in Europe under Sky Watcher brand with the name "Heritage 130p".
It's a Newtonian reflector on a Dobsonian mount. It has an aperture which is large enough to show you details on Jupiter, Saturn, and Mars (around opposition, at least).

In between the €50 binoculars and the €200 reflector there are many achromatic refractors, but I hesitate to recommend any of these because you mainly want to observe planets:
When light passes through a refracting telescope's objective lens, different wavelengths are diffracted different amounts, and this results in some colour separation which is most noticeable with bright objects.
Planets are some of the brightest objects we observe.

Also, many of the aforementioned refractors also suffer from less-than-brilliant build quality, which is another reason to go for the the 130mm reflector. Here's how I think about it:
At this price point you want to make sure that as much of your money as possible is going into what's important: the optics.
Anything else: bundled eyepieces, diagonals, tripods, equatorial mounts, ...all of this costs money, and money going into these components is money that isn't going into the optics.
This is why a Newtonian reflector on a Dobsonian makes the most sense: the optics are mirrors and the mount is a couple of bits of wood. Telescopes don't get any more simple than that :-)

You mentioned in a comment that it was hard to find the Heritage 130p in Europe.
Right now it's hard to find any telescopes anywhere - the pandemic has created a lot of new amateur astronomers and has also affected supply from China.
Here's a short list of European shops I can think of which you might want to check out:

Astroshop
Bresser
First Light Optics
Teleskop Service

Of these, if you're looking for good deals then keep and eye on Bresser's and FLO's special offers pages. (If you're in the EU then be careful ordering from FLO because they're based in the UK and you'll have to pay additional taxes on your orders). Bresser is probably the place where I've managed to get the best deals.
Finally, consider buying second-hand. Your money will go a lot further.


If we found evidence of life on Mars, how would we know that it originated on Mars rather than Earth? Consider this scenario.  One of the probes sent to Mars either very soon, or within the next century, finds conclusive micro-fossil evidence that life once existed on Mars.

One theory today that is quite common is that life might that have arisen on Mars was then ejected into space, floated to Earth and then seeded life on our planet.

I'm tracking with you and that could make sense, assuming we found the conclusive evidence for life on Mars.  However, why would we assume that the early martian life originated on Mars, rather than Earth?  Is it not likely that somewhere between 2.5-3 billion years ago, a major volcanic eruption or meteor impact could have hit an earth teeming with simple-life and sent it hurdling through space to Mars?

I understand that my theory has the gravity of the sun working against it, but I also see it not being entirely impossible.  I mean, 100 years ago, one could assume that life originating on Mars and then being sent this was was ridiculous and impossible but now it's a rational, viable theory.

Considering such a scenario, how would scientist verify that these life-forms didn't originate from Earth, rather than Mars?  It seems to me that this question is the first question that would need to be asked and answered after the fossil-records were found and verified.

Why would we assume that the early martian life originated on Mars,
  rather than Earth?

There's still a whole lot we don't know.  As Wayfaring stranger points out in the comments, Origin is a whole different question.  It's possible that life originated outside our solar system and came to either Mars and/or Earth from outside the solar-system.   I don't think anyone who studies this idea is "Assuming" life originated on Mars, only that the idea has a chance of being true.

  Is it not likely that somewhere between 2.5-3 billion years ago, a
  major volcanic eruption or meteor impact could have hit an earth
  teeming with simple-life and sent it hurdling through space to Mars?

As I understand it, volcanic eruptions are unlikely to send anything into space unless it's a smaller sized moon.   The escape velocity (young earth, maybe 10 km/s, young mars, maybe 3-4), volcanic eruptions, as far as I know, don't shoot things out at 10,000 - 20,000 MPH.   But meteor impacts of sufficient size can do that.

Mars is a better meteor debris making target than the Earth cause it's smaller, so the gravity is lower and presumably it's mostly had a thinner atmosphere too.  We've found martial meteors on Earth.   We might not find any Earth meteors on mars cause it takes a much bigger impact to knock bits of rock off Earth and because the Atmosphere slows objects down, both coming in and going out.

  I understand that my theory has the gravity of the sun working against
  it, but I also see it not being entirely impossible.

The sun isn't as big a factor as you might think.  Once something is knocked off a planet and it gets into orbit around the sun, gravitational assists can move it around further out or further inside the solar system.  What presumably happens is that, with a big enough impact, many thousands if not millions of bits of debris get into solar-system orbit and from there, some of them land on other planets - probably much less than 1% of those hit Earth, but if it carries life that can survive the trip, all you need is one rock.

  I mean, 100 years ago, one could assume that life originating on Mars
  and then being sent this was was ridiculous and impossible but now
  it's a rational, viable theory.

While that's true, the "People used to think this was impossible" isn't a scientific approach for what might be true.   We should determine what is possible and/or thought to be likely, based on physical evidence, not what wasn't understood 100 years ago.   Your example is a good point on why it's important to keep an open mind about the unknown.   You can still make theories based on evidence, and keep an open mind on the unknown.  There's really no conflict between the two.

  Considering such a scenario, how would scientist verify that these
  life-forms didn't originate from Earth, rather than Mars? It seems to
  me that this question is the first question that would need to be
  asked and answered after the fossil-records were found and verified.

It's a good question.

The simple answer is that Mars cooled first and Mars (likely) had oceans first, so it's a better candidate to have developed life first though extremophiles can live in hot oceans, so . . . time will tell.


Please help explain this unknown light in the sky. Not ISS. Not a star or comet. Too slow So a few nights ago I walked outside on my front lawn and sat down on the tailgate of my truck. I was facing north. I was looking down and towards the house across the street. Out of no where a bright light caught my eye. I looked up and didn't see anything. A couple of seconds later another light appeared, then disappeared. I pin pointed it to the left of the left of 'Kochab' star in 'Ursa Minor.' I was locked onto the sky at that point... So I kept watching and it kept happening. It was irregular. Zero regularity; it kept doing this. Bright flashes of light and subtle growing of light for a 20 minute period moving towards the north east. Randomly doing this with 2 seconds, sometimes with 5-7 second intervals. Even the type of flashing was irregular. Sometimes flashing following by flashing and other times growing light following by growing light. I've never seen anything like this in my life. I know what the space station looks like, I've seen it countless times as well as space junk. They're constant lights. And we all know what planes look like in the night sky. Constant red lights with regular blinking of white light. It was traveling in a straight path with little to no noticeable curvature. In no way could it have been reflecting light. No doubt it was projecting its own light.

Anything similar you've known or heard about? Please help explain this.

That sounds like a high altitude nonfunctioning satellite to me. For example, a rocket body or upper stage that is tumbling. I have seen these types of satellites flash  many times before.

The pattern is irregular because of the spinning and changing angle to the Sun.


Questions about amateur astrophotographer Nik Szymanek's telescope The 2011 Sixty Symbols video Spy Satellites (from Deep Sky Videos) shows amateur astrophotographer Nik Szymanek and his telescope.

Question: Can someone identify the model and design of this particular telescope and it's mount, and explain why there are so many baffles inside the tube (isn't this more than typical?) and the structure of the tube? Is it some composite? Why the spiral pattern?

click all images for full size

Szymanek says he took some of his Flickr images with a GSO 10" Ritchey-Chrétien telescope.
At least one third party offers these with Altair Astro branding and says the tube is made of carbon fiber.

The Ritchey-Chrétien design is a Cassegrain with hyperbolic primary and secondary mirrors.
It minimizes coma and spherical aberration at the expense of field curvature.
The baffle tube forward of the hole in the primary is required to shade the image plane from direct skylight.
Many Cassegrain telescopes also have a short baffle tube aft of the secondary.

The multiple baffle rings inside the main tube just darken the tube more completely than black paint alone.
They are more likely separate rings than a continuous helix.
The alternative would be to roughen the surface e.g. with flocking paper.

The mount looks like an older Software Bisque Paramount, a robotic German equatorial mount.
On current models the declination axis housing is cylindrical rather than rectangular.


Does Alpha Process Produce Bismuth? In the book "Horizons: exploring the universe-Cengage learning (2018)", p200, it states that:

Helium fusion produces carbon, and some of the carbon nuclei absorb helium nuclei to form oxygen. A few of the oxygen nuclei can absorb helium nuclei and form neon and then magnesium. Some of these reactions release neutrons, which, having no charge, are more easily absorbed by nuclei to gradually build even heavier nuclei. These reactions are not important as energy producers, but they are slow-cooker processes that form small traces of heavier elements right up to bismuth with atomic weight 209, nearly four times heavier than iron. Many of the atoms in your body were produced this way.

Base on my question previously, I assume we are talking about the alpha process here. And when I check the Wikipedia of the Alpha Process, it says that the alpha process ends at $^{56}_{28}\mathrm{Ni}$ due to photodisintegration, but as the suggests, the process should produce $^{209}_{83}\mathrm{Bi}$. The question is, why do Bismuth, an atom with atomic number $83$ are produced here? Shouldn't atom like $^{}_{82}\mathrm{Pb}$ with even atomic number being produced here?

Bismuth is produced via the s-process.
It is the slow absorption of neutrons that can produce heavier elements beyond the peak of the binding energy per nucleon curve at iron. The alpha process isn't capable of producing much of anything beyond nickel.


What is the current size of the SN1006 supernova remnant? I was enamored by the wikipedia article of SN1006.  Esp. the fact that it was so bright, it could cast shadows on the ground.  (Even this idea that you could have possibly read parchment with just the light from the supernova.  Source).

The Question is basically what is the width (radius?) of the remnant as seen in this picture.

You were so close! The answer was actually given lower down on the Wikipedia page: roughly 20 parsecs. Since one parsec is about 3.26 light-years, we can calculate that that comes out to about 64 light-years, as this seems to corroborate. The outer layers of the remnant are expanding outward at an outrageous rate - 11 million miles per hour, according to NASA. I invite you to do the calculations to figure out how large it will be at a certain point in time.


Consequences of strong wind on an alien Planet on the possibility of life I was surprised to learn recently that Neptune has winds of 1500 miles an hour.

My question is whether life could ever evolve on such a Planet that has such powerful winds? Not necessarily on Neptune of course but on another exoplanet in another Solar System.

We know that life can start and evolve quite well on a planet with 250 mph winds: You're living on one. The jet stream can reach this speed in the Earth's atmosphere.

Beyond that it is speculation. While not much is going to survive on the surface if there are surface winds of 1500mph at a static pressure of anything like 1atm, I can see no problem of life developing in the depth of the ocean no matter what the wind speed is.

However I futher suggest that 1500mph winds cannot happen at the surface of a terrestrial planet that is anything like the Earth. The extreme conditions needed to create a surface wind of 1500mph on a daily basis may prevent any kind of life as we know it. But then the winds are not the acutal problem but the conditions needed to produce them.


Is time taken into account by astronomers when creating and using maps of the universe? There's really two questions I'm asking.

Firstly, when maps are produced of stars and galaxies, are they just produced as we see them now from our viewpoint? Or are they based on the motion of those bodies? Eg Galaxy X is 1 million light years away and we know it's moving at Y speed, so it's real position now is actually 1 million years worth of movement along that trajectory.

Secondly, are those things taken into account when doing other studies of things like dark matter? Ie things are actually further apart than what we see because we're seeing them as they were Z million years ago. I would expect that would affect calculations for things like how much 'missing' matter there was.

To try to further clarify this second question, simplifying things to 3 points on a triangle... if we're at A and we observe points B and C which are X billion light years apart, then the effect of gravity on the speed of B and C moving apart would have been greater in the past when they were closer together and furthermore the effects of the current gravitational force will take more than X billion years to reach the other object. As far as I understand, dark matter is a way to account for observed gravitational effects that can't be accounted for in other ways. When astronomers do these calculations, can I assume that they have taken into account the time delay in the effects of gravity between galaxies? Or have I in my naivety, stumbled on some profound insight! (I doubt it.)

For the first part of your question, @userLTK has already provided a very good explanation, and I believe that by introducing redshift, the second part of your question is also partially answered. I will try to expand a little on it, hoping that I have understood your question correctly. To start off, I'm going to go ahead and quote my own thesis (not yet published);

  [W]hen moving to celestial distances we quickly realise that time measurement ambiguity also arises. To combat this we tend to not describe distances to objects directly, but relate these properties to an object’s relative line-of-sight velocity with respect to us.

This is why, when NASA earlier this year announced the Hubble Space Telescope having observed the most distant galaxy yet, the distance to the galaxy was never mentioned. The distance is not a direct observable, and has to be calculated based on certain assumptions. One direct observable we do have, is the line-of-sight velocity, which we express in terms of redshift. By describing objects in terms of redshift, we simultaneously have a "distance" measurement to the objects, as well as knowing how fast they move away from us.

When we make observations and try to learn more about things like the energy content of the universe (radiation, regular matter, dark matter, dark energy), the redshifts of the objects we observe are crucial. We consider various models of the universe, and see how they compare with what we observe on different redshifts. I very quickly found back to a paper written by my supervisor some years back; figure 7 in there shows you that kind of comparison.

Personally, I am working on something which I hope will lead to us being able to see whether dark energy evolves over time. In doing that, knowing the redshifts of the objects are crucial to my work, and I constantly need to keep in mind the implications of the distant objects' movement away from us. It is simply a factor I need to multiply or divide by in my calculations, to make sure I am comparing the correct things with each other.


Observing the motion of the solar system and galaxy through space? This is very perplexing.
Conditions:

planets are moving around the sun (solar system)
solar system is moving as part of the galaxy
the galaxy is moving through space on some axis
galaxy is part of a cluster, also moving through space
other stars and constellations are also moving through space, presumably in the same direction and speed as the Milky way.

I appreciate the answer to Why is the Solar Helical (Vortex) model wrong? - but considering the question: how can we observe the solar system's Helical motion through space, I have a new question... please allow me to present both, since they are related.
Question 1:
Again, how can we observe the Helical motion of our solar system (and galaxy) from earth? Is it by observing the passing of planets across/through constellations?
Question 2:
If I can make an analogy: like different ticking clocks stored inside a grandfather clock - is the solar system following its own Helical motion and therefore are all other solar systems within the Milkyway also following their own Helical motion? AND is the galaxy also following its own Helical motion!?
OR!
Is the solar system's motion fixed (Helically speaking), and any such movement is tied to the motion of the parent, i.e. the galaxy? In other words, is the Helical motion of the solar system the same as the galaxy, or are all solar systems moving Helically through space, e.g. many clocks within a grandfather clocks analogy.
Initially, the question was simple: how can be observe the solar system's Helical motion?
But it seemed unintuitive to me that the solar system is moving Helically while the galaxy is also moving as such - both structures on their own trajectory and paths - seems like galactic chaos.
And, all the while planets maintain their fixed orbits.
I would have guessed that the solar system is NOT moving Helically, but the galaxy is, and the solar system is simply a fixed orbital passenger, as so to speak - in the same way 8 grains of sand (planets) are passengers in a bowl of jelly (galaxy), both being carried by another vehicle (cluster).
It seems to me then, the solar system's motion through space is limited by the galaxy's motion, in terms of axis, speed - and therefore the galaxy is also fixed like a passenger on a much larger galaxy cluster.
It seems reasonable to suggest the whole universe is moving Helically(?), and all galaxies merely inherit this, but are more like grains of sand in jelly than independently ticking clocks within a larger grandfather clock.
If our solar system is moving Helically independently from the galaxy, the solar system could move at its own speed, either quicker or slower depending on environmental factors. Could the solar system really skip-out of the galaxy, racing ahead on its own Helical path(?).
So many questions! But Question 1 is the one I wish to request help answering.

All motion is relative. There is no absolute space which can be said to be the correct reference frame in which we must measure all motion. Hence, for any object you're free to construct any reference frame that does, or does not, give that object a helical motion.
Reference frames
Of course, some reference frames make more sense than others. When you cycle to work, it makes sense to measure your speed relative to the bike lane. The reference frame of the Sun makes sense if you're concerned with planets' orbit. In this frame, Earth has no helical motion, only circular motion. Or you could call it helical motion with $v_z = 0$, if you wish.
On the other hand, the Sun and its neighbors follow a path through the Milky Way; the so-called Local Standard of Rest, measured by observing nearby stars and star-forming regions. In this frame, Earth has a (non-$v_z\!\!=\!0$) helical motion.
Similarly, in the reference frame of Milky Way's path toward, say, Andromeda, the Sun has a helical motion. Another star will have a similar, but different, motion.
Comoving coordinates
That said, there is one reference frame which has a special status, namely the Universe's comoving frame. These are the coordinates that expand along with the Universe, and they are the coordinates in which everything on average is at rest. If you hear the phrase "Milky Way's motion through space", this is probably what is referred to. Since time flows differently in different frames, it's also the frame of choice when you talk about the age of the Universe. Likewise, since lengths are contracted in moving frames, the comoving frame is the frame in which we measure cosmological distances.
It's important to realize, however, that motions, positions, etc. measured in the comoving frame are no more "correct" than in any other frame.
The cosmic microwave background
But how can we measure a velocity in this reference frame, if all motion is relative?
One way would be to measure the motion of a million galaxies with respect to us, and take the average. But a much easier method, which is in fact how we do it, is to measure the dipole of the cosmic microwave background (CMB). This radiation was emitted when the Universe was very young, and has the special property that it was emitted isotropically (i.e. the same in all directions) with a near-perfect Planck spectrum.
Hence, if you standing still in the comoving frame, you will see exactly the same CMB spectrum in all directions, whereas if you're moving you will observe the CMB to be blueshifted in front of you, and redshifted behind you. This difference between the two opposite directions is called the dipole, and its value was measured by the Planck satellite (Planck Collaboration 2020) to imply a total velocity of the Sun in the comoving reference frame of
$$
v_\odot = 369.82\pm0.11\,\mathrm{km}\,\mathrm{s}^{-1},
$$
toward the Galactic coordinates
$$
\{\ell,b\} = \{264.021^\circ\pm0.011^\circ, 48.253^\circ\pm0.005^\circ\}.
$$
Note the amazing precision, with an uncertainty in speed and direction of only 400 km/h and less than an arcminute, respectively!
This velocity is important to know, since it is used to correct all measured cosmological velocities.


What would happen if someone had a telescope and watched Betelgeuse when it goes supernova? Would that person go blind?

Neutrino detectors and the abundance of Neutrinos would detect the upcoming visible show about 3 hours before any visible signs, so there would be time to point certain telescopes that could handle the brightness towards it.

I'm curious if an individual with a telescope pointed in that direction would have an unpleasant surprise.    Would the scientific community be wise to not announce the massive stellar explosion until after it's visible to avoid potential negative effects from over-eager amateur astronomers.

I realize this is a kind of silly question and it might depend too much on the telescope, but I'm curious.

No, it would not be a problem. Supernovae are not at all like flashbulbs – they brighten over a period of many days and dim again even more slowly. Here are a number of different light curves taken from Wikipedia:

The rise is fast on an astronomical scale – several orders of magnitude over a period of roughly ten days – but very slow on a human scale. An amateur looking at it would not notice any significant change in brightness, but if the same person came back a few hours later or the next night, the change would be very evident.

As far as we can tell, the reason is that the light at peak brightness is caused by emissions from material blown off by the explosion. For example, in Type 1a SNe, most of the light is from the radioactive decay of the huge mass of ejected nickel-56 (half life 6 days).

The Wikipedia article on supernovae is quite good and covers this all in more detail.


How do you figure out the magnitude of stars? How do you figure out the star magnitude of a star? Do they just give it a guess or what?
If not, how do they figure it out accurately?

You must remember that there are Absolute magnitude (that measured from a fixed distance of 10pc) and Apparent magnitude (which is measured from Earth).

Historically magnitudes ranged from First to Sixth and were assigned by guess by Ptolomaeus. His First Magnitude was the equivalent of saying first size, so it was the brightest, and Sixth Magnitude was the assignment he made for the dimmest seen with the naked eye.

Nowadays, we use roughly the same scale but with real numbers, ranging from -26.74 (Sun) up. We defined the star Vega to be the exact 0.0 apparent magnitude (and 0.0 colour in all filters, for the case), and then we use the formula

$m_1-m_{ref}=-2.5log{I\over I_{ref}}$

to define all other apparent magnitudes from that one by measuring Intensities.

So to answer you, yes, we measure apparent magnitudes rather accurately. For stars other than Sun, they range from -1.46 for Sirius up to +8 in a perfect night for a trained naked eye (typically +6 for the normal eye on a normal, far from city lights, night).

Reference http://en.wikipedia.org/wiki/Magnitude_(astronomy)


Why does the adiabatic exponent decrease at the ionization zones? The context is the ionization zones in stellar atmospheres or interiors, the Sun, for instance.

The adiabatic exponent is the heat capacity ratio:

$$\gamma = \frac{c_P}{c_V} = \frac{C_P}{C_V}$$

And, for an ideal gas, it can be shown that  $\gamma=(f+2)/f$ where $f$ is the degrees of freedom. Resulting in $\gamma\approx1.66$.

In most of the extent of the solar interior, $\gamma\sim1.66$ but it presents dips when ionization is present, like the H, HeI and HeII ionization zones. My question is why does this happen?

I thought it could be because when ionization, the heat is used to ionize atoms instead of increasing the temperature and, therefore, the heat capacity would be larger in those regions. But, because the $\gamma$ is the ratio between the heat capacities, the argument does not work.

Any suggestion?

There are two things going on. (1) When you add heat to a gas that is on the threshold of ionisation or partially ionised, some of that heat goes into ionisation. This means that it takes a much larger amount of energy to produce a rise in temperature. (2) However, as the gas becomes ionised the number of particles per unit mass also increases and so the pressure increases at a given temperature. The net effect is that $C_V$ (heat capacity for a fixed volume) increases by more than $C_P$ (heat capacity for a fixed pressure) and so the adiabatic index decreases.

It is a tricky and detailed computation to work out how $C_V$ and $C_P$ change as ionisation proceeds. An example calculation for pure hydrogen gas is give on pp 123-126 of "Principles of stellar evolution and nucleosynthesis" (1983, D. Clayton). Both $C_V$ and $C_P$ increase drastically (by factor of 30-40) as ionisation increases, both peaking at around 50% ionisation before falling back to exactly twice their unionised values once the gas is completely ionised (when it just behaves like a monatomic perfect gas but with twice the number of particles per unit mass). However, the behaviour of $C_V$ and $C_P$ are slightly different, $C_P$ increases by less than $C_V$, and so the ratio of $C_P/C_V$ changes and goes through a minimum at around 50% ionisation before regaining the standard monatomic gas value once completely ionised.


Is intrastellar commonly used by astronomers to refer to objects within our solar system? The CNET article Interstellar comet Borisov looks ordinary, making Oumuamua even weirder says:

  A paper published Monday in Nature Astronomy lays out the early data on Borisov, which is just the second-ever object seen visiting our solar system from beyond. While scientists will get a better look as the comet comes closer to Earth over the next several weeks, so far it looks to be the same color and size as most ordinary comets. Earlier research also revealed it's behaving in familiar ways with a tail containing some of the same toxic gases we expect from intrastellar comets.

(ArXiv)

Is the word intrastellar commonly used to refer to objects within our solar system by astronomers, or is it just the editors creative reversal of interstellar.

Along the same lines, would extrasolar be used by astronomers to refer to objects outside of our solar system?

No. (I'll note that this usage is arguably erroneous, since the nominal meaning of "intrastellar" is "within or inside a star".)

First, I personally have never heard anyone use that term in my twenty-five-odd years as an astronomer.

Second, a full-text search of the astronomical literature on the NASA Astrophysics Data System turns up a grand total of 51 sources that use "intrastellar" (as opposed to, say, 325,000 hits for "intracluster"). None of these has anything to do with the Solar System. Quick checks of a few of them show a mixture of simple typos (i.e., "intrastellar" used when "interstellar" is clearly meant), awkward/failed attempts at synonyms for "intracluster stellar light", and actually correct uses meaning "inside a star".

  would extrasolar be used by astronomers to refer to objects outside of
  our solar system?

You mean like "extrasolar planets", the discovery of which shared the Nobel prize in physics this year? In practice, "extrasolar" seems to be used mainly to refer to other solar systems and the components thereof, rather than just anything at all outside the solar system. (Though I have seen "extrasolar dust" used to refer to dust grains found in the Solar System but thought to have originated outside it.)


Notifier about visible ISS passes and/or Iridium flares for Ubuntu PC I am trying to find application that would be capable of notifying me about
visible ISS pases for specified location and/or visible Iridium flares for specified location.

This software must be capable of running on Ubuntu.

I strongly prefer active open-source projects.

I know that there are multiple mobile apps but I want something that may run on Linux PC.

To avoid "this is subjective" - I will be happy about any software fulfilling this requirements and criteria are not subjective.

Here is something that I wrote for my personal purposes.

Fetches iridium flare details based on your heavens-above credentials and displays a notification in Ubuntu.

Github

I had one for ISS passes as well. Will find it and push it to the repo soon.


Is the light we see from stars extremely old? Our nearest star Proxima Centauri is 4.243 light years away from Earth.

Does that mean we are seeing light that is 4.243 years old everyday?

Yes, the speed of light in vacuum (or c) is 299,792,458 m/s and one light-year is the distance the light travels in one Julian year (365.25 days), which comes out as 9.4605284 × 1015 meters. Since c is the maximum speed at which all energy, matter, and information in the Universe can travel, it is the universal physical constant on which the light-year (ly) as one of the astronomical units of length is based.

That means that visible light as an electromagnetic radiation cannot travel faster than c and in one Julian year it can traverse a maximum distance of

  d = t * c

d is distance in meters

t time in seconds

c the speed of light in vacuum in meters per second

If we calculate this distance for a 4.243 ly distant object, that comes out as 4.243 * 365.25 * 86,400 s * 299,792,458 m * sˉ¹ or exactly 40,141,879,395,160,334.4 meters (roughly 40 trillion kilometers or 25 trillion miles).

That is the distance the light traveled since it was last reflected of (or in our case emitted from, since Proxima Centauri is a red dwarf star) the surface of a celestial object to be 4.243 Julian years later visible at our observation point, in this case our planet Earth from where the distance to Proxima Centauri you quoted was measured.

The more powerful the telescope, the further into the past we can see because the light is much older! This goes the same regardless of the distance of the object you're observing, but astronomy is particularly neat in this regard and we can observe objects that are so distant that we see them from the time when they were still forming.

For further reading on other units used to measure far away objects you might be interested in reading this question on the parsec.


What would happen if asteroid 99942 Apophis collides with the earth? In the news recently it's been said that in 2029 the asteroid called Apophis, aka 'The God of Chaos', will fly by very close to earth. To quote Geek.com

  In 2029, a massive asteroid called 99942 Apophis will fly past our
  planet at an approximate distance of 19,000 miles within the distance
  of some orbiting spacecraft.

It's said the chances of a collision are about 1 in 100,000, which is small but not not completely infeasible either.

The asteroid has a diameter of around 350 meters with a mass of 4×10^10 kg and an average orbital speed of around 30km/s.

What kind of damage could we expect on earth if it were to collide with us?

If it hits the deep ocean, not much relatively speaking. In the recent past, people wildly exaggerated the capability of an asteroid (at least ones in the size range of Apophis) to cause massive tsunamis; in reality, the ocean efficiently and quickly absorbs the impact. That said, it'd still be terrifying to see such an impact in deep water.

If it hits a city, it would cause violent devastation, immediately killing 10's or 100's of thousands with its initial impact, and millions with the resulting shock wave and debris.


Does science need support from religion or philosophy to explain the creation? Science is trying to explain how the universe is made. The beginning of the universe explains the Big Bang theory. But what happened before Big Bang? Science cannot go before that. So, does this mean that always there be space for religion and philosophy to explain things that science cannot?

The question seems to be based on the notion "before". This notion relies of the concept of the arrow of time, meaning time "flowing" in some "direction". The arrow of time itself is based, among others, on the notion of "time".

The Planck epoch - the first epoch of the current Big Bang model - lasted a little less than $10^{-43}\mbox{ s}$. That's the shortest unit of time. To ask within this short time interval for an arrow of time doesn't make any sense. Hence a before/after didn't exist within  the Planck epoch, and hence asking for a "before" isn't meaningful within the Planck epoch.

The Planck epoch to be able to exist needs the mere existence of space and time, not yet an arrow of time.

The cause for the existence of space and time at all is a matter of the pre-Planck epoch. In this phase using any notion which is based on space or time isn't meaningful. Cause and effect in the temporal sense, which underly most "why?"-questions, are based on time, and are meaningless in this epoch.

It's possible to construct other "pre-Big-Bang" models. But it's hard to find observational evidence for any of them.

If you suggest a creator of whatever kind, you just push the ultimate question a little bit further to the "past", and making it much more complicated. How could a creator be created, able to create such a complex thing like the universe? You need a chain of ever more complex meta-creators without end.

If you argue, that the first creator doesn't need a cause to exist, this applies also for the universe, formed from a pre-Planck medium. Hence nothing would be won.

Therefore it's rather unlikely, that religion or philosophy could be able to provide a more satisfying answer than science.

(Here some metaphysical multiverse theories.)


How is a non-rotating black hole created How are non-rotating black holes formed?

I guess that non-rotating black holes are formed from non-rotating stars but I couldn't find any proof that such a star exists on the internet. If this is true can you also put up an example of such a star?

Does the matter absorption of a non-rotating black hole differ from a rotating black hole?

All stars have some angular momentum. Conservation of angular momentum when the core of a star collapses means that it is very likely that most black holes are rapidly rotating, just as newly-born neutron stars are observed to be extremely fast-rotating.

Even if one were to have a star with a non-rotating core as it collapsed, the subsequent accretion of material with angular momentum would give the black hole that angular momentum.

Non-spinning black holes are a theoretical ideal that is unlikely to be found in nature.

The details of the accretion of material onto a black hole are complex and still the subject of theoretical and observational research. But yes, the details of accretion in spacetime governed by the Kerr metric appropriate for rotating black holes will differ from those of a non-rotating Schwarzschild black hole. Kerr black holes have an "ergosphere", outside their event horizons, where material is force to co-rotate with the black hole.


Why does any planet look like a (not so) big white ball through my telescope? I have a 130mm (5") diameter Newtonian reflector with a 650mm focal length (f/5). I have collimated my telescope already but when I'm looking at Mars or Jupiter (not a star I'm sure), all I see is a white dot. Even if I use my 6mm with a 2x barlow, Mars still looks like a white dot but with a liiittle bit of a gray shade like a 3/4 moon. Of course I focused my eyepiece before. Why can't I see Mars or any other planet better than that ?

It seems that you haven't align properly your finder (or) laser. You can align at day with a chimney, but at night you must start with the moon and after that you are sure that you are pointing correctly move to a well known feature (like Pleiades cluster in Taurus) and try to find it with the scope (after that you can move to a star (maybe Mizar in Ursa Mayoris or Albireo in Cygnus if you are in the northern hemisphere) after that you must be sure that the finder and laser are pointing correctly.

Other question is that (probably) you are using a very high magnification with that telescope. I have myself a RTF newtonian 114 / 500 and I usually works with 20 mm eyepice (that is 25x), you are using about 216x that is almost the maximum theorically magnification for that aperture. Maybe you should use the 6 mm eyepiece without the barlow (that is 108x more or less) this should be enough but with cheap optics that could be a very high magnification also. I think that you could try with a bigger eyepiece... maybe 15mm plössl (30x and about 1.5º of size)


What would happen if Jupiter and Earth were at the same distance as the Moon is from Earth? If Spock came with a super machine capable of moving planets, and placed Earth so close to Jupiter as the Earth's moon, the gravity of Jupiter would make us fall into it?

That's no good idea. Earth wouldn't necessarily fall into Jupiter in the short run, provided it orbits Jupiter fast enough (within about 1.7 days), and on a circular orbit, but we would risk to collide with Io, destroy it by tidal forces, or change its orbit heavily.
The other Galilean moons would get out of sync and change their orbits over time.

Tides would be severe on Earth, not just limited to oceans, but also for "solid" ground, as long as Earth isn't tidally locked. This would result in severe earth quakes and volcanism.

Our days would be dim due to the distance to the sun. After tidal locking of Earth and ejection/destruction of Io the tides as heat source would be lost, oceans would freeze, temperature would fall to about -160°C mean temperature. During the polar night oxygen would probably condense from the atmosphere and form lakes, may be even nitrogen. By this atmospheric pressure would drop.

Since Spock is smart enough to know these consequences in advance, he wouldn't do it.


What is the relative velocity between planets in different solar systems? Is it possible to estimate what the difference in velocity is between the earth and another convenient exoplanet? Or perhaps just our star and a near neighbour?

I'd be curious where I could find the figures, and I'm wondering exactly what the magnitude of the difference is between relatively near neighbours.

Context:

Putting together an outline for a book, and I'm curious about something.

In the book, faster-than-light travel happens through instant travel between two points in space. In doing so, you retain all of your kinetic energy. This means you'll emerge at your destination with the same velocity as you had before you transitioned.

The bulk of the travel time in interstellar travel would simply be matching velocity with your destination before transition - the vast majority of the distance of the journey would be instantaneous, since for traffic control reasons ships are expected to come in at a reasonable speed when compared to their destination.

Tens of kilometres per second for nearby stars. Hundreds of km/s for stars in distant parts of the galaxy to thousands of km/s for stars in nearby galaxies. Anything from "much more" to "it's complicated" for stars in very distant galaxies.

The Earth is orbiting the sun at 30km/s and the orbital velocity of exoplanets is on the same order of magnitude. The stars are also moving relative to the sun. We can measure the transverse velocity for nearby stars by seeing them slowly change position (relative to the distant background stars) and we can measure the radial velocity by the blue- or red-shifting of the light.

We can't directly measure the transverse velocity of distant stars, but their general motion is around the galaxy with a velocity, relative to the sun, in the 100s of km/s

Nearby galaxies are moving at similar velocities. Again, we can currently only measure the radial velocity, but their transverse velocities would be of the same order of magnitude, and in the 100s to 1000s of km/s.

Distant galaxies are part of the Hubble flow, and the expansion of space, so defining relative velocity or relative distance becomes tricky and needs to be done in the context of General Relativity, at which point things become more problematic, and beyond what is required for space opera.

For context, spacecraft in orbit around the Earth travel at less than 8 km/s and our fastest spacecraft (which are needed to travel close to the sun) have never reached 30km/s.


Age of earth relative to other planets Relative to the average age of other known planets, is the earth young, old or in the middle? Does it make a difference if you compare the earth against nearby planets (say < 500 LY), or other planets in our galaxy, or other galaxies?

We do not have direct data on the age of any exoplanets, but we can estimate the age of their host stars, around which they presumably formed at the same time. These methods are uncertain and may have systematic biases but gives at least some information. If we use the Wikipedia page and plot the ages (again, both old data and now extra selection biases!) the resulting distribution looks like this:

The mean age is 4.9161 Gyr and the median age is 4.5260 Gyr, comparable to the age of the Earth. The skew distribution means Earth is younger than the mean, but fairly typical.

Another way of estimating whether Earth is young or old is to compare to star formation rate estimates across the history of the universe. This is of course also presently uncertain and may be different in different galaxies (elliptic galaxies have low star formation, so their planets would tend to be older than the ones in spiral and irregular galaxies). Overall, it appears to have peaked 3.5 Gyr after the big bang and has declined since. That would perhaps make the average planet that ever formed much older ($\approx 10$ Gyr old) than Earth.

However, many of these have also been "lost" since they formed around bright stars that died long ago and are not measured in the exoplanet surveys. There is also the issue of whether early low-metallicity stars form many planets: it might be that planet formation got going much later (Lineweaver has a -- somewhat old -- paper arguing that Earth formed after 75% of the other planets). Again, this is a very active research field and future answers are likely to be better.


If an asteroid was to collide with Earth, how much warning would we have? I was talking to my 9-year-old son about the Florence asteroid that is passing close to the earth. He wanted to view youtube videos about that asteroids, and we saw the starting of this one https://www.youtube.com/watch?v=UzxMbkrNbcg and when I realized that the title video has 2036 as the year in which an asteroid crashes into the Earth. I explained that that was science fiction (like Back to the future) and only an animation

He asked me: "If an asteroid or similar object was to collide with the Earth,.... how many years or months before the crash occurs would the scientific community know?"

I suppose that the advance time depends on technology, so assume the current level of technology.

Asteroids come in all shapes and sizes, and generally the bigger they are the easier they are to detect.

Small asteroids, from a the size of sand grains (properly called meteoroids) to a few meters across hit the Earth everyday without causing harm and are undetectable until they hit (we call the trace as they hit the atmosphere a meteor) They cause no damage. For such objects we get 0 hours warning.

Somewhat larger objects can cause some local damage For example the Chelyabinsk asteroid caused damage from broken glass in Russia. Objects this large may be detected a few hours to a few days. The Chelyabinsk asteroid wasn't, and hit with no warning. We have observed some small asteroids just prior to them hitting the atmosphere.

We have found large numbers of objects whose orbit can bring them close to Earth. Every object we have found has an orbit that misses Earth.  With each new object that is located we can forecast its orbit for several centuries. However new objects are being found all the time. It is possible that a object will be discovered that has the potential to cause damage to a wider area. If the object happened to be on an orbit that had it collide with Earth then there could be less than a year's warning. That is very unlikely. It is slightly more likely that an object will be discovered to be on a collision course only after several orbits, in which case there would be years or decades warning.

Very large objects that could threaten the survival of humankind are rare. There are some such objects, (larger than Florence). We hope that we have now detected all very large near Earth asteroids, and discoverd them to be non-threatening (like Florence is not a current threat to Earth)

Finally a comet may be on a collision course with Earth. Comets that are spotted are usually detected a few months before they could threaten Earth. But comets are much rarer than asteroids.

In summary, between 0 hours and a century, with several decades being likely for an object that could do widespread damage.

The particular object referred to in the video is Apophis. It is roughly 400m asteroid that is not going to hit the Earth for as long as we can forecast. It will, however, pass close by in 2029, and again in 2036. In 2005 the uncertainty in orbit was such that we could not rule out a collision in 2036. Further observations in 2006 and after allowed and a more accurate orbit to be calculated, and showed that it would certainly miss.


How can I observe the Orionid Meteor Shower? I would like to see the orionids sometime this week (October 20-26, 2013). What is the best way for me to observe them by naked eye?

Also, would I be benefitted by trying to look at them with a telescope or or are they too fast and spontaneous for most amateurs to capture?

While this shower is now largely over, the way to best observe meteors is the same for all showers in principle (including coming showers like the Leonids around November 17 and Geminids around December 14).

The name of most showers reference the name of the constellation their radiant (point in the sky the meteors seem to be coming from) lies in. In the case of the Orionids, this is the constellation of Orion, so look in the general direction of (and around) Orion.

As you suggest, meteors appear unexpectedly and move too fast to be caught with a telescope.  The best way to observe them is to lie down comfortably and use the naked eye.  The key word is "comfortably": find a comfortable reclining garden chair or lilo and lie down.  That's one half of the comfort; the other is to stay warm.  Even when watching the Perseids in summer you're lying still under an open sky, and for the fall/winter showers mentioned here you'll really want to bundle up and perhaps take a thermos with a hot drink.

The comfort is important - there may be several minutes between two meteors and hence lying down is a good way to relax while watching, which will allow you to stay out longer and see more.  It is definitely more relaxed than standing up with your head in your neck.

One other tip for "comfort": many people will enjoy this more in the company of other enthousiasts, and if you're one of them you should consider going out with a few other people.  It will allow you to discuss the meteors just sighted to pass the time between events, or even to help each other to see one (if they're not too fast).


Adjust axis labels in ds9 How can I adjust the axis labels in ds9?

I'd like to have something like:

So far I only managed to get floating points (tl h%f3):

or the leading hours are missing (tl h%f1 m):

Edit:

I tried "tlhm.1" as kindly suggested by Jeremy, but unfortunatly it still does not work:

The DS9 Reference Manual, p42, 'Numeric Formats'. http://ds9.si.edu/doc/ref/ref.pdf#page48 has a bunch of information.

Based on that, I expected that "tlhm.1" would achieve what you proposed.

However, it seems that SAOImage DS9 is very keen on dropping leading hours it sees as unnecessary, even if you have specified them in a format specifier.

I haven't been able to figure out a format specifier combination that retains the hours for every gridline while also showing the minutes or seconds.

I have searched elsewhere for advice on this and haven't found it either. In fact, I haven't been able to find any comment on the hours being suppressed, nothing that explains why it does this, nor even anyone else remarking or complaining about it.

I suggest sending an email to the DS9 Help Desk address found in the menu under Help > Help Desk.


What is meant by "short lived" in the duration of a planetary nebula? In this wikipedia article, it describes planetary nebula as "short-lived," but I'm not sure in relation to what?  This could mean billions of years in some contexts.

How long is short-lived?

Bonus if there are any useful rules of thumb in astronomy terms for future uses (how stars timelines are described, versus galaxies, etc.)

In the case of planetary nebulae we are talking of ~10,000 years (follow the link to the main article on Planetary Nebulae).

In general a short lifetime for a phenomena means a time short compared to the total life of the entity it is related to. It is an informal term and does not have a fixed maximum value, but 10,000 years is a short time on most astronomical scales.


Origin of heavier elements on earth? Earth is part of Solar system, which is said to have originated from condensation and mutual attraction in dense clouds of gasses and dust. If Sun is basically more than ninty percent hydrogen and rest is helium. Nuclear fusion inside sun is said to pause near iron(56/26) and also several other planets like Jupiter and Saturn are gas giants. Where did heavy metals and other heavy elements on earth come from if second most nearest star(/star-system) is some four light years away (and mass would take long to come from those sources) ?

Different types of stars are responsible for creating different groups of elements via nucleosynthesis. Most of the "lighter" metals (Na, Al, Ga, Ge, Se), were formed by exploding massive stars, and most of the "heavier" metals (I, Ir, Ag, Au, Pt, U, Pu) were created by merging neutron stars. Exploding white dwarfs are partially responsible for elements like Ti, V, Cr, Fe, Co, Ni. Dying low mass stars were involved with the creation of some of the elements Sr, Y, Zr.

The following periodic table of elements (from Wikipedia), shows the elements color coded according to their source of creation.

All the elements on Earth were created by various stars that seeded our region of the universe prior to the formation of our solar system.


Planets positions (azimuth, altitude) API I'm looking for a simple API that will allow me to get positions of planets and the moon for a given date, location and time.
Does anyone know an API like that?
Any suggestions or alternatives would be appreciated.

Astropy is one option:

from astropy.time import Time
from astropy.coordinates import solar_system_ephemeris, EarthLocation
from astropy.coordinates import get_body, get_moon
from astropy.coordinates import SkyCoord, EarthLocation, AltAz
from astropy import units as u
import time;

t = Time("2019-08-11 11:00", scale="utc")
loc = EarthLocation(lat=38.2464000*u.deg, lon=274.236400*u.deg, height=0*u.m)

with solar_system_ephemeris.set('jpl'):
  moon = get_body('moon', t, loc)

altazframe = AltAz(obstime=t, location=loc, pressure=0)
moonaz=moon.transform_to(altazframe)

print(moonaz.alt.degree,moonaz.az.degree)

If you want a library you can ship with a product, you'll want something much smaller.  I am actually working on a library converted to many different languages to do just that.
 Only the JavaScript version has a working Alt Az example, but it should be easy to convert to other languages (and will be eventually).


Lunar Soil: what are those "bumps" and how were they formed? I was watching a video of the chinese lunar landing and saw numerous bumps in the soil. What are they? Is there any theory that explains how they came into existence?

It's a bit difficult to understand what exactly you're asking about, but I will presume you meant the topological features in images like this one, taken from the video of which you provided a link to:

For the most part, they are meteorite and micrometeorite impact craters, with some regolith boulders and impact ejecta scattered along the edge of the larger impact crater at the bottom right of the image.

These impact craters appear strange to an untrained eye when they're the only visible feature on images, because there is not atmospheric scattering of light on the Moon that would somewhat illuminate the shadow side too and reduce contrast to what we're used to seeing on Earth, so the high contrast can appear as bumps or dents interchangingly and at will, similar to how you can see either either a vase / candlestick in the middle (yellow) or two faces facing each other (black) on this image:

A trained eye will have less problems recognising them for what they are, though. One nifty trick is to search the image for different looking topological features, such as already mentioned larger crater ejecta along its edge at the bottom right of the image, or perhaps prominent features within the features themselves, like some larger micrometeorite impact craters show shockwave formed uplifted centers, and so on. It also helps to understand how these features were likely made, but once you orient yourself, it will prove difficult to convince yourself into seeing what you saw initially, if you saw indentations where there are perturbations, or vice versa.


How to convert magnitudes to bolometric luminosity? If we know a star's magnitudes from several bands(say u,g,r,i,z,J,H,k) and the star's distance, how to calculate Lbol?

Let's suppose the star has a black body spectrum. Is there any manual about the calculation? It's better to have a lot of technical details.

Quoting from Wikipedia,

  The bolometric magnitude Mbol, takes into account electromagnetic
  radiation at all wavelengths. It includes those unobserved due to
  instrumental pass-band, the Earth's atmospheric absorption, and
  extinction by interstellar dust. It is defined based on the luminosity
  of the stars. In the case of stars with few observations, it must be
  computed assuming an effective temperature. Classically, the
  difference in bolometric magnitude is related to the luminosity ratio
  according to:

$ M_{bol,*} - M_{bol,sun} = -2.5log_{10}(\frac{L_*}{L_{sun}})$

  In August 2015, the International Astronomical Union passed Resolution
  B2[7] defining the zero points of the absolute and apparent bolometric
  magnitude scales in SI units for power (watts) and irradiance (W/m2),
  respectively. Although bolometric magnitudes had been used by
  astronomers for many decades, there had been systematic differences in
  the absolute magnitude-luminosity scales presented in various
  astronomical references, and no international standardization. This
  led to systematic differences in bolometric corrections scales, which
  when combined with incorrect assumed absolute bolometric magnitudes
  for the Sun could lead to systematic errors in estimated stellar
  luminosities (and stellar properties calculated which rely on stellar
  luminosity, such as radii, ages, and so on).

[leading to the accepted definition of]
$ M_{bol} = -2.5log_{10}(L_*) + 71.1974... $ , where the constant term is the zero-point luminosity $L_0$ .

Dunno if this helps, other than that you have to determine the spectral luminosity of the star in question.


Why is the Earth-Moon distance not the same at each perigee/apogee? I wonder why the Earth-Moon distance is not the same at each perigee/apogee. Isn't the Moon's orbit a fixed ellipse with Earth at one of the foci? If it is so, shouldn't the distance at perigee/apogee be a fixed value?

Isn't the Moon's orbit a fixed ellipse with Earth at one of the foci?

No, it's not. This isn't even true for the planets' orbits about the Sun. Each planet perturbs the orbits of the other planets, making Kepler's ellipses approximately correct rather than exact. The Moon's orbit is strongly perturbed by the Sun in a number of ways. The Moon's orbit deviates from being a fixed ellipse in a number of ways. One result of these solar perturbations (and to a much lesser extent, perturbations from Venus and Jupiter, and to an even lesser extent, from the other planets) is that the Moon's orbit precesses in a number of ways.

One such precession is the apsidal precession. The line from the Earth to the point at which the Moon reaches perigee does not point to a fixed position in space. It instead precesses with a period of about 8.85 years. This is what results in the so-called supermoons, which occur when the Moon's orbit is close to perigee when the Moon is full.

Another such precession is the nodal precession. The line of nodes (where the Moon crosses from above to below the ecliptic, and vice versa), also precesses, but with a period of about 18.6 years. We only get eclipses when the Moon is very close to a node at a syzygy (either a full Moon, resulting in a lunar eclipse, or a new Moon, resulting in a solar eclipse).


Was the Sun's gravitational lensing observed in other solar eclipses than the one in 1919? In 1919 the gravitational lensing by the Sun has been observed during a total solar eclipse. Did someone observe the lensing in any other total eclipses? Last year there was a total eclipse in Chile and there were many scientists observing it. Did they see the stars in different places too? I mean, today it must be even easier to observe it with current telescopes or something. But there is no mention of any other observations than the one in 1919, is there?

Yes, observations of this kind are within the technical scope of amateur astronomers.  Several groups succeeded in replicating the experiment during the 2017 eclipse that crossed the USA.

For example Donald Bruns measured deflections of 2.8 arcseconds of multiple stars.

Nasa published a "How To" page for anyone wanting to test GR themselves.


What is CMB radiation doing to the universe? It is said that due to CMB radiation our universe has been expanding? Firstly what lead the universe to expand? What do scientists mean by dark energy? Will energy convert into matter?

It is said that due to the CMB radiation our universe has been expanding?

No. It's the the other way round. The CMB is the result of the expansion of space. In the initial stages after the birth of the universe, there was hot plasma everywhere and light could not travel much farther. The universe was opaque at that time. But slowly as the Universe cooled and atoms began to form, light could travel farther. This light got redshifted due to the expansion of space and can be now detected as the CMB radiation. It's in the microwave region of the spectrum and just above absolute zero(about 2.7 K).

  What do we mean by Dark Energy?

After Hubble's discovery, we came to the conclusion that the Universe is expanding. We expected the expansion to slow down as time progresses but what we observed as that the expansion was accelerating and is still doing so. Physicists and cosmologists did not have any explanations for this and so it was named "Dark Energy". Dark in the sense that it is unknown.


I can't find Rigel on Tycho 2 catalogue I'm trying to develop a planetarium using Tycho 2 catalogue.

To read it I use the WCSTools. But I have a problem.

On Wikipedia I have found that Rigel star has RA: 05h 14min 32,3s and Dec: -08º 12’ 06’’. I have translate them to decimal degrees (78.6375, -8.2017). I've used that to find it on Tycho 2 catalogue (file catalog.dat) but I can't find it.

To search into the catalogue I have used the function TY2READ from ty2read.c file.

And this is how I search the star:

void ReadTy2Catalog()
{
    double raCenter = 84.5;
    double decCenter = -1.2;
    double raDistance = 10.;
    double decDistance = 10.;

    int nMaxStars = 20000;

    char* filePath = "D:\\Fuentes\\Repos\\Planetarium\\StarsCataloguesLib\\Resources\\";
    Ty2Read read;

    read.Read(
        filePath,
        TYCHO2,         /* Catalog code from wcscat.h */
        raCenter,       /* Search center J2000 right ascension in degrees */
        decCenter,      /* Search center J2000 declination in degrees */
        raDistance,     /* Search half width in right ascension in degrees */
        decDistance,    /* Search half-width in declination in degrees */
        0,              /* Limiting separation in degrees (ignore if 0) */
        0,              /* Inner edge of annulus in degrees (ignore if 0) */
        1,              /* 1 to sort stars by distance from center */
        WCS_J2000,      /* Search coordinate system */
        2000.0,         /* Search coordinate equinox */
        0.0,            /* Proper motion epoch (0.0 for no proper motion) */
        -20.0,          /* Limiting magnitudes (none if equal) */
        30.0,           /* Limiting magnitudes (none if equal) */
        1,              /* Magnitude by which to sort (1 or 2) */
        nMaxStars,      /* Maximum number of stars to be returned */
        1);             /* Verbose*/
}

I have checked all the stars returned and none has Rigel's RA and DEC.

What am I doing wrong?

This frustrated me as well when I first used the Tycho-2 catalog. Not finding a well known bright star can be disconcerting. Quoting from http://heasarc.nasa.gov/W3Browse/all/tycho2.html

  Supplement-1 (not part of this HEASARC database but available at
  ftp://cdsarc.u-strasbg.fr/cats/I/259/suppl_1.dat.gz) lists stars from
  the Hipparcos and Tycho-1 Catalogues which are not in Tycho-2.

I only skimmed that file, but I think this might be the line you're looking for:

5331 01752 1|H|078.63446353|-08.20163919|    1.9|   -0.6|  0.6|  0.5|  0.7|  0.5| | 0.312|0.012| 0.283|0.010|999|T| 24436

(the "-0.6" is the U-B color index, not the magntiude)


Why does the Sun have different day lengths, but not the gas giants? The Sun's rotation period varies from about 25 days at the equator to about 38 days at the poles. As I understand it, this is because the Sun is not solid, and because of the way centripetal force works, the equator must move faster than the poles.

Question: if this works, why do Jupiter/Saturn/Uranus/Neptune have well-defined days? Why don't the equators of these planets rotate faster than the poles as well? For example, Wikipedia's article on Jupiter gives the length of a Jovian day as 9h 55m 30s, which is so precise that it implies Jupiter does not have a rotational period which varies with latitude.

It's a matter of how "day" is defined.

Wikipedia's article on Jupiter cites this IAU/IAG paper for the length of a Jupiter day.  In it, footnote (e) of table I has the following:

  The equations for W for Jupiter, Saturn, Uranus and Neptune refer to the rotation of their magnetic fields (System III)

The radio emissions of the gas giants have well-defined periodic variations.  These variations are caused by the rotation of the magnetic fields of those planets, and are evidence that they have a reasonably coherent core of some sort that's rotating at a uniform speed.  The periodic variations then represent the rotation speed of that object, which is taken as the rotation speed of the planet.

We're reasonably certain the Sun doesn't have a coherent core.  Measuring the variation of the magnetic field doesn't show a well-defined period, and doesn't provide a useful definition of the Sun's rotation speed.


How does a planet lose mass to its host star? How do bodies like WASP-12b lose mass to its central body? The process is never really explained in popular media, instead showing visualisations of a thin veil of gas being "sucked" in a rather straight line (and then into a ring around the star) rising straight from the surface of the planet. I highly doubt the mechanics which these illustration insinuate: Gravitation isn't working like a vacuum cleaner on a dusty rug. Either the rug goes with it, or the dust stays on the rug. The only mechanism that I can think of are particles from the upper atmosphere which happen to pick up enough thermodynamic energy so that they are faster than the escape velocity of the planet. But is this a process which effects a big enough mass transfer to be of significance? Do I overlook something? How is such a mass defect going on really?

In the case of WASP-12b, at least, the close proximity to the star has actually deformed the planet so much that it is overflowing its Roche-lobe, the area around a planet or star that . We can show this mathematically by finding the approximate Roche-lobe of the planet using:

$\frac{r_1}{A}=.46224\sqrt[3]{\frac{M_1}{M_1+M_2}}$  for $\frac{M_1}{M_2}<.8$ (which it is)
where $A$ is the orbital separation and $r_1$ is the radius of the Roche-lobe around $M_1$.
Solving for $r_1$ we get $97788\pm 2318$ miles. The planet's radius is $77759 \pm 3909$ miles. Taking the best possible scenario, there would be $\approx$ 13,000 miles between the planet's surface and its Roche-lobe if the planet was a perfect sphere. It is unknown how much the star affects the planet, but it would not be a stretch to think that the major axis of the planet would be 13,000 miles longer than the minor axis, allowing for the planet's gas to be shoved out of the Roche-lobe and "sucked" into the star.


Is this photocomposition of Andromeda's galaxy and the Moon accurate? I recently saw the below image circulating around twitter/facebook/reddit. It is titled "Andromeda's actual size if it was brighter"

One of the comments provides a link to another comparison provided by APOD, and the following comment mentions that the first one I linked seems a bit off.

Is the first image accurate in term of relative sizes? What is the relative angular size of Andromeda's galaxy and the Moon?

The Andromeda Galaxy's angular size is about 178x63 arc-minutes and the Moon is about 31 arc-minutes wide. Relatively speaking, the Andromeda Galaxy's apparent size is nearly 6x2 Moons.

So from the photo, their relative sizes in the sky appears to be very roughly accurate. The galaxy appears to have been superimposed from another image just to show what the galaxy might look like in the sky if it were brighter.


Why we can't see our Sun as it was a few years ago? Our Sun is orbiting the center of the Milky Way galaxy. So many years ago, it was at a different location from where it is now.
In addition, we are observing stars and exoplanets as they were many years ago, for example stars like Sirius..

In this case, why can't we see our own Sun in its orbital path a few hundred years back.
Is there any specific reason why we can't see/observe our Sun from the past?

Our Sun moves through the galaxy much slower than light does. So the light that was emitted last year by the Sun is already very far away from the Earth. Therefore, we don't receive any light from (i.e. we don't see) the Sun as is was last year.

As an analogy, image walking along and shooting bullets in all directions. The bullets are going much faster than you can go by walking, so you won't ever get hit by your own bullets. But someone walking next to you can get hit by the bullets you are shooting out.


Are meteors visible on Mars? If a person were standing on the surface of Mars, under ideal viewing conditions for seeing a meteor: no clouds, the sun has long set, would a meteor be visible to the naked eye considering how thin the Martian atmosphere is?

First Shooting Star Seen from Mars

  space.com  2005

  The background image shows the meteor near the top-left and the horizon at the bottom. A red arrow shows the direction of travel. The inset is a larger version of the meteor itself. The graph is a "light curve" that aided in tying the meteor to comet Wiseman–Skiff.
  (Image: © Nature/NASA/Spirit/F. Selsis et al.)

This was made by Spirit's panoramic camera, so it probably would be visible to the naked (helmeted) eye.


Heat from other Stars Does the Earth receive any heat at all from the millions of other Stars in our Galaxy ? Is it light that is bringing the heat and perhaps it cools down on the long journey in Space getting to the Earth and that's why no significant amount of heat is getting here ?

Yes, the Earth does receive energy from the stars, but not much. The effective temperature of the night sky is about 3 Kelvin which is not much more that that of the cosmic microwave background at 2.7 Kelvin. The difference being due to the total energy of starts etc.(room temperature is ~295 kelvin)

The coldness of the night sky is interesting in itself see Olber's Paradox


Would gravitational waves be subject to external gravitational perturbations? Given that the gravitational wave detected by LIGO was a very weak echo of a very distant event, could it have been "deviated" and distorted on its way here by a sufficiently massive black hole in between?

Would a black hole, since it traps even light, and since gravitational waves travel at the speed of light, absorb some portion of the gravitational wave and leave a "shadow" in its propagation such that if a black hole was between your instrument and an incoming gravitational wave you would have no way to detect it?

If so wouldn't the mass distribution in the Universe look less homogeneous at larger scales (as observed), since gravitational waves would not deform space uniformly and would instead need to "equalize" by forming voids like the Boötes void, and filament structures like the Pisces–Cetus Supercluster Complex or Sloan Great Wall?

If not, how could a gravitational wave from a distant event possibly affect the gravity well of a black hole closer to the observer? It doesn't seem possible to me that the attenuated ripple in space time from an event so far away could pass right through the gravity well of a closer local black hole like a galactic supermassive black hole.

Firstly, gravitational waves (GWs) are not an echo - we measure the direct signal.

The process you describe here is known as gravitational lensing, the deviation of (usually) light rays due to massive objects between the source and the observer.  This also applies to GWs.  The result will be similar - the direction of the waves can be changed, resulting in a distorted image of the source and possibly a 'brighter' image (stronger signal) due to 'gravitational focussing'.

However, LIGO and Virgo do not image GWs, they detect point sources.  Hence, there is no distorted image, but the 'luminosity' of the signal may be affected, resulting in a (somewhat) misjudged distance (although they use a 'luminosity distance', which is not necessarily the same as a current physical separation).

Just as in the case of light, a black hole could trap some of the GW signal that would have reached the observer (gravitons that fall directly into the black hole), if it is directly between the source and the observer, but the gravitational focussing makes it likely that the resulting signal will be stronger rather than weaker.


Would one have to be more than halfway to the Oort Cloud for the Sun to appear as bright as the full moon? Is this correct?  If the Sun is 400,000 times brighter than the full moon am I correct in figuring that one would have to be about 632AU from the Sun for it to appear as bright as the full moon.  If the Oort Cloud begins about 1000AU from the Sun, one would have to be more than 60% the way to the Oort Cloud for the Sun to appear as bright as the full moon.

Yes, brightness is inversely proportional to the square of the distance, and the square of 632 is about 400,000. It's probably appropriate to round the value to 1s.f. to give "600AU".  Of course, at that distance the sun appears point-like.

The distance to the Oort cloud is rather hard to define. It's not like you reach 1000 AU and see a Star Wars like "Asteroid field" of comet nuclei. For example Wikipedia gives a distance of 2000AU.


How long does it take the center of the Earth to complete a full orbit? If we take midnight of 1/1/2017 in any country and mark in space where the center of the Earth is located, at what date, in the same country, has the center completed a full orbit.

I am almost certain that has to be 1/1/2018, but I am not so sure about the hour.

It's not exactly one year because of the 28/29 February thing.

The exact period is 365 days 6 hours 9 minutes 9 seconds [Random House Encyclopedia. New York: Random House: 174.]


Understanding Earth Tilt, Sun's Position and Lattitude Calculation I've been trying to figure out how to calculate the latitude of my location with just the shadow of a stick cast by the sun. I am doing this under the assumption that I am stranded in some place with no almanac or any other data. (not even day or month).

I want to find the latitude roughly. But I have problems picturing the globe along with it's tilted axis and the angles formed by the shadow.

Could you help me understanding the concept and give me a definitive picture of angles that can be calculated. A perspective like a side-view of the earth and sun (orbiting plane - perpendicular to the screen) would help me understand much better.

Here is my efforts to understand so far -

I am not an expert nor have a good background in maths (my maths teacher ruined my life). So please explain me in simple words.

I've been trying to figure out how to calculate the latitude of my
  location with just the shadow of a stick cast by the sun. I am doing
  this under the assumption that I am stranded in some place with no
  almanac or any other data. (not even day or month).

You really cannot find your latitude with only the sun and sticks at your disposal and no declination data or time data. Maybe if you could record your shadow over a period of a day, you could tell if you are in the northern or southern hemisphere by observing which way the shadow moves. If it moves clockwise, you are in northern hemisphere.

And if you could repeat and observe for 365 days (from the day you are stranded, assuming you are very accurately measuring the angles) you could find if you are within the tropic of cancer or above it, as you might not have the sun right on top of your stick over the year if you are above the 23.5 N parallel.

And that's as far as you can get. To determine the precise location, you will need the sun's declination at any given time. May be you will get lucky, if the day you are measuring the angle and the equinox matches, but you wouldn't know it.

  Could you help me understanding the concept and give me a definitive
  picture of angles that can be calculated.

A picture is worth thousand words. And an interactive demonstration... It's worth at least a hundred 2D diagrams.

Additional Interactive media - http://astro.unl.edu/naap/motion1/animations/seasons_ecliptic.html


Have we detected galaxies which have red-shifted beyond the visible light range? According to this answer it is possible for galaxies' light to move beyond the visible frequencies due to redshift:

It is possible that eventually the light from them could move into the infrared and even
the microwave in extreme cases.

Could this have already happened?  Have we already looked for it?  Is there a telescope with the instrumentation to detect galaxies' 'light' at these wavelengths?

Yes, of course. Many, many examples. Telescopes work in the infrared, far-infrared and there are even samples of galaxies that are selected on the basis of their mm emission.

The most distant galaxies detected now have redshifts of 7 or more. This means the wavelength of their light has been stretched by a factor $1+z$ - i.e. by a factor of 8. Thus light in the visible range, say 500nm, now appears at wavelength of 4 microns, in the infrared.

Telescopes that work in this range include the Spitzer space telescope; and many ground-based telescopes. Observations of highly redshifted galaxies are routinely made at infrared wavelengths on telescopses all around the world.

Galaxies are also detected in the far infrared by the Herschel satellite or at mm (getting on for microwave) wavelengths by JCMT or the ALMA telecope.


"LinAlgError: SVD did not converge in Linear Least Squares" with eleanor.py I'm doing some tests with eleanor module (i'm a novice). I'm using the example code written on eleanor.py website
from IPython.display import Image
import warnings
warnings.filterwarnings('ignore')

import eleanor
import numpy as np
import matplotlib.pyplot as plt
from astropy.coordinates import SkyCoord

eleanor.Update(sector=1)

star=eleanor.Source(tic=38846515, sector=1)
print ('-------------------------------------')
print ('-------------------------------------')
print ('-------------------------------------')
print ('')
print ('')
print ('Found TIC {0} (Gaia {1}), with TESS magnitude {2}, RA {3}, and Dec {4}'
.format(star.tic, star.gaia, star.tess_mag, star.coords[0], star.coords[1]))

data = eleanor.TargetData(star, height=15, width=15, bkg_size=30, do_psf=True, do_pca=True, regressors='corner')

plt.figure(figsize=(15,5))

q = data.quality == 0

plt.plot(data.time[q], data.raw_flux[q]/np.nanmedian(data.raw_flux[q])+0.06, 'k')
plt.plot(data.time[q], data.corr_flux[q]/np.nanmedian(data.corr_flux[q]) + 0.03, 'r')
plt.plot(data.time[q], data.pca_flux[q]/np.nanmedian(data.pca_flux[q]), 'g')
plt.plot(data.time[q], data.psf_flux[q]/np.nanmedian(data.psf_flux[q]) - 0.02, 'b')
plt.ylabel('Normalized Flux')
plt.xlabel('Time [BJD - 2457000]')
plt.title('WASP-100')
plt.show()

After running the program, it find the star with its magnitude and coordinates, but appears this error:
LinAlgError Traceback (most recent call last)
c:\Users\gabri\OneDrive - Università degli Studi di Padova\Desktop\eleanor prova.py in
23
24
---> 25 data = eleanor.TargetData(star, height=15, width=15, bkg_size=30, do_psf=True, do_pca=True, regressors='corner')
26
27 plt.figure(figsize=(15,5))

C:\Python36\lib\site-packages\eleanor\targetdata.py in init(self, source, height, width, save_postcard, do_pca, do_psf, bkg_size, aperture_mode, cal_cadences, try_load, regressors, language)
227 self.create_apertures(self.tpf.shape[1], self.tpf.shape[2])
228
--> 229 self.get_lightcurve()
230
231 if do_pca == True:

C:\Python36\lib\site-packages\eleanor\targetdata.py in get_lightcurve(self, aperture)
623 norm = np.nansum(self.all_apertures[a], axis=1)
624 all_corr_lc_pc_sub[a] = self.corrected_flux(flux=all_raw_lc_pc_sub[a]/np.nanmedian(all_raw_lc_pc_sub[a]),
--> 625 bkg=self.flux_bkg[:, None] * norm)
626 all_corr_lc_tpf_sub[a]= self.corrected_flux(flux=all_raw_lc_tpf_sub[a]/np.nanmedian(all_raw_lc_tpf_sub[a]),
627 bkg=self.tpf_flux_bkg[:, None] * norm)

C:\Python36\lib\site-packages\eleanor\targetdata.py in corrected_flux(self, flux, skip, modes, pca, bkg, regressors)
1235 f = np.arange(0, brk, 1); s = np.arange(brk, len(self.time), 1)
1236
-> 1237 lc_pred = calc_corr(f, cx, cy, skip)
1238 corr_f = flux[f]-lc_pred + med
1239

C:\Python36\lib\site-packages\eleanor\targetdata.py in calc_corr(mask, cx, cy, skip)
1175 # temp_lc = lightcurve.LightCurve(t, flux).flatten()
1176 tmp_flux = np.copy(flux[np.isfinite(flux)], order="C")
-> 1177 tmp_flux[:] /= savgol_filter(tmp_flux, 101, 2)
1178 SC = sigma_clip(tmp_flux, sigma_upper=3.5, sigma_lower=3.5)
1179

C:\Python36\lib\site-packages\scipy\signal_savitzky_golay.py in savgol_filter(x, window_length, polyorder, deriv, delta, axis, mode, cval)
333 x = x.astype(np.float64)
334
--> 335 coeffs = savgol_coeffs(window_length, polyorder, deriv=deriv, delta=delta)
336
337 if mode == "interp":

C:\Python36\lib\site-packages\scipy\signal_savitzky_golay.py in savgol_coeffs(window_length, polyorder, deriv, delta, pos, use)
135
136 # Find the least-squares solution of A*c = y
--> 137 coeffs, _, _, _ = lstsq(A, y)
138
139 return coeffs

C:\Python36\lib\site-packages\scipy\linalg\basic.py in lstsq(a, b, cond, overwrite_a, overwrite_b, check_finite, lapack_driver)

LinAlgError: SVD did not converge in Linear Least Squares

I tried to find solutions, like installing numpy and scipy from conda, but they did not solve the problem. Anyone know how to deal with it?
EDIT:
I solve the issue by creating a conda environment, but if I run the program with py IDLE it crashes anyway.

I installed eleonor and ran your code - similar but deleted the line:

eleanor.Update(sector=1)

Because it was giving me an error. And it runs without issues.
Attached I post my output. I’m guessing you must have some problems with the packages themselves. I can't pinpoint what, but my naive advice would be to create a conda environment (I can try and help if you need). In this new and empty conda environment, you install the packages that you import (as you did before), then give it a run.