question: How do we know out about other galaxies and far planets when they're thousands of light years away? can telescopes really see that far?
comment: Short answer: No, telescopes can't really see that far. Long answer: What they can see are the effects of light as it passes through galaxies, star clusters, planets, and nebulas. For example; a couple of years back the Hubble Space Telescope was able to spot a galaxy 13.4 billion light years away, and snap a pretty decent picture of it (Messier 63). Folks at NASA and some artists got together and came up with an "artists rendition" ([ URL_1 ]( URL_1 )) based on the kinds of light we see from that galaxy. There's a whole lot of very complicated, but educated, guesswork going on here. What the Hubble Space Telescope really saw was this; [ URL_2 ]( URL_0 ) That light, having taken so long to reach us, must have come into existence around 400 million years after the beginning of the universe, which is actually far older than we even thought possible for a galaxy this size. We can tell that the light took that long to reach us by measuring its "red shift", which is a cheeky way of measuring how much the universe has expanded since that light began its journey. GN-Z11 has a red shift of 11.1, which beats out the previous contender for "furthest observed object" by quite a bit (EGSY8p7 had a red shift of 8.68).
passages: Section::::Eyes on the Exoplanets.
  
  Based on data from the NASA exoplanet archive, Eyes on the Exoplanet enables uses to zoom in on more than 1000 planets orbiting distant stars. Exoplanets can be filtered by relevant criteria such as Earth-sized, large rocky planets, gas giants, etc. Distances to these planets are expressed in travel time by car, plane, etc.
  
  Section::::Eyes on the Earth.
   The first answer to this problem was speckle imaging, which allowed bright objects with simple morphology to be observed with diffraction-limited angular resolution. Later came NASA's Hubble Space Telescope, working outside the atmosphere and thus not having any seeing problems and allowing observations of faint targets for the first time (although with poorer resolution than speckle observations of bright sources from ground-based telescopes because of Hubble's smaller telescope diameter). The highest resolution visible and infrared images currently come from imaging optical interferometers such as the Navy Prototype Optical Interferometer or Cambridge Optical Aperture Synthesis Telescope, but those can only be used on very bright stars.
   For instance, an object with a relatively low surface brightness such as the moon cannot be observed, because its light is too diluted. Only targets which are at temperatures of more than 1,000°C have a surface brightness high enough to be observed in the mid-infrared, and objects must be at several thousands of degrees Celsius for near-infrared observations using the VLTI. This includes most of the stars in the solar neighborhood and many extragalactic objects such as bright active galactic nuclei, but this sensitivity limit rules out interferometric observations of most solar-system objects. Although the use of large telescope diameters and adaptive optics correction can improve the sensitivity, this cannot extend the reach of optical interferometry beyond nearby stars and the brightest active galactic nuclei.
   Many modern telescopes and observatories are located in space to observe astronomical objects in wavelengths of the electromagnetic spectrum that cannot penetrate the Earth's atmosphere (such as ultraviolet radiation, X-rays, and gamma rays) and are thus impossible to observe using ground-based telescopes.
   BULLET::::- Eclipsing binaries — In the last decade, measurement of eclipsing binaries' fundamental parameters has become possible with 8-meter class telescopes. This makes it feasible to use them as indicators of distance. Recently, they have been used to give direct distance estimates to the Large Magellanic Cloud (LMC), Small Magellanic Cloud (SMC), Andromeda Galaxy and Triangulum Galaxy. Eclipsing binaries offer a direct method to gauge the distance to galaxies to a new improved 5% level of accuracy which is feasible with current technology to a distance of around 3 Mpc (3 million parsecs).
   Section::::Giant Magellan Telescope.
   The ability of Spitzer to see through dust and thick gases is good for galactic nuclei observations. Massive objects at the hearts of galaxies shine in x-rays, gamma rays, and radio waves, but infrared studies into these clouded regions can reveal the number and positions of objects.
   BULLET::::- 1989 — Margaret Geller and John Huchra discover the "Great Wall", a sheet of galaxies more than 500 million light years long and 200 million wide, but only 15 million light years thick,
  
  BULLET::::- 1990 — Michael Rowan-Robinson and Tom Broadhurst discover that the IRAS galaxy IRAS F10214+4724 is the brightest known object in the Universe,
   As a science, the study of astronomy is somewhat hindered in that direct experiments with the properties of the distant universe are not possible. However, this is partly compensated by the fact that astronomers have a vast number of visible examples of stellar phenomena that can be examined. This allows for observational data to be plotted on graphs, and general trends recorded. Nearby examples of specific phenomena, such as variable stars, can then be used to infer the behavior of more distant representatives. Those distant yardsticks can then be employed to measure other phenomena in that neighborhood, including the distance to a galaxy.
   Section::::Definitions.
  
  Modern ellipsometers are complex instruments that incorporate a wide variety of radiation sources, detectors, digital electronics and software. The range of wavelength employed is far in excess of what is visible so strictly these are no longer optical instruments.
  
  Section::::Definitions.:Single-wavelength vs. spectroscopic ellipsometry.
   Section::::Infrared technology.
  
  One of the most common infrared detector arrays used at research telescopes is HgCdTe arrays. These operate well between 0.6 and 5 micrometre wavelengths. For longer wavelength observations or higher sensitivity other detectors may be used, including other narrow gap semiconductor detectors, low temperature bolometer arrays or photon-counting Superconducting Tunnel Junction arrays.
  
  Special requirements for infrared astronomy include: very low dark currents to allow long integration times, associated low noise readout circuits and sometimes very high pixel counts.
   An additional infrared survey, the Two-Micron All Sky Survey, has also been very useful in revealing the distribution of galaxies, similar to other optical surveys described below.
  
  Section::::Modern observations.:Telescope observations.:Optical rays (visible to human eyes).
   Initially, there were four ASAS-SN telescopes at Haleakala and another four at Cerro Tololo, an LCOGT site. Twelve more telescopes were deployed in 2017 in Chile, South Africa and Texas, with funds from the Moore Foundation, the Ohio State University, the Mount Cuba Astronomical Foundation, China, Chile, Denmark, and Germany. All the telescopes (Nikon telephoto f400/2.8 lenses) have a diameter of 14 cm and ProLine PL230 CCD cameras. The pixels in the cameras span 7.8 arc seconds, so follow up observations on other telescopes are usually required to get a more accurate location.
   Section::::Commonly observed objects.
  
  The most commonly observed objects tend to be ones that do not require a telescope to view, such as the Moon, meteors, planets, constellations, and stars.
   For large ground-based telescopes, the resolution is limited by atmospheric seeing. This limit can be overcome by placing the telescopes above the atmosphere, e.g., on the summits of high mountains, on balloon and high-flying airplanes, or in space. Resolution limits can also be overcome by adaptive optics, speckle imaging or lucky imaging for ground-based telescopes.
   The NIROSETI survey has been designed for observing several thousand objects over a few years, and commenced full operations on 28 January 2016. During a clear night of observations, about 20 to 30 objects are observed. Because infrared light penetrates farther through gas and dust than visible light, this search will extend to stars thousands of light-years away. The initial target sample is mostly main-sequence and giant stars located within 50 parsecs from Earth, drawn from the Breakthrough Listen program target list.
   The brightest sources of low-frequency radio emission (10 MHz and 100 GHz) are radio galaxies which can be observed out to extremely high redshifts. These are subsets of the active galaxies that have extended features known as lobes and jets which extend away from the galactic nucleus distances on the order of megaparsecs. Because radio galaxies are so bright, astronomers have used them to probe extreme distances and early times in the evolution of the universe.
  
  Section::::Modern observations.:Telescope observations.:Infrared.
   The field of view of binoculars is rarely more than eight degrees, while that of typical amateur telescopes may be substantially less than one degree, depending on the magnification used. Many objects are best observed using higher magnifications, which inevitably go along with narrow fields of view.
  
  Section::::The technique.
   The number of known HH objects has increased rapidly over the last few years, but that is a very small proportion of the estimated up to 150,000 in the Milky Way, the vast majority of which are too far away to be resolved. Most HH objects lie within about one parsec of their parent star. Many, however, are seen several parsecs away.
   The surface brightness fluctuation (SBF) method takes advantage of the use of CCD cameras on telescopes. Because of spatial fluctuations in a galaxy's surface brightness, some pixels on these cameras will pick up more stars than others. However, as distance increases the picture will become increasingly smoother. Analysis of this describes a magnitude of the pixel-to-pixel variation, which is directly related to a galaxy's distance.
  
  Section::::Extragalactic distance scale.:D–σ relation.
   BULLET::::- Department of Physics, Montana State University
  
  BULLET::::- NASA Goddard Space Flight Center
  
  BULLET::::- NASA Marshall Space Flight Center
  
  BULLET::::- Plasma Physics Laboratory, Princeton University
  
  BULLET::::- Instrumentation and Space Research Division, Southwest Research Institute
  
  BULLET::::- W.W. Hansen Experimental Physics Laboratory, Stanford University
  
  BULLET::::- University of California Los Angeles
  
  BULLET::::- Center for Astrophysics and Space Sciences, University of California, San Diego
  
  BULLET::::- Center for Astrophysics and Space Astronomy and Joint Institute for Laboratory Astrophysics, University of Colorado at Boulder
  
  BULLET::::- Department of Physics and Astronomy, University of Rochester
  
  Section::::See also.
  
  BULLET::::- Daniel K. Inouye International Airport
  
  BULLET::::- List of solar telescopes
   BULLET::::- Optical astronomy was the earliest kind of astronomy. Telescopes paired with a charge-coupled device or spectroscopes are the most common instruments used. The Earth's atmosphere interferes somewhat with optical observations, so adaptive optics and space telescopes are used to obtain the highest possible image quality. In this wavelength range, stars are highly visible, and many chemical spectra can be observed to study the chemical composition of stars, galaxies and nebulae.
   Relatively cheap, mass-produced ~2 meter telescopes have recently been developed and have made a significant impact on astronomy research. These allow many astronomical targets to be monitored continuously, and for large areas of sky to be surveyed. Many are robotic telescopes, computer controlled over the internet (see "e.g." the Liverpool Telescope and the Faulkes Telescope North and South), allowing automated follow-up of astronomical events.
   As the atmosphere is transparent for radio waves, radio telescopes in space are of most use for Very Long Baseline Interferometry; doing simultaneous observations of a source with both a satellite and a ground-based telescope and by correlating their signals to simulate a radio telescope the size of the separation between the two telescopes. Observations can be of supernova remnants, masers, gravitational lenses, starburst galaxies, and many other things.
  
  Section::::Particle detection.
   Gravitational wave detectors are being designed that may capture events such as collisions of massive objects such as neutron stars or black holes.
  
  Robotic spacecraft are also being increasingly used to make highly detailed observations of planets within the Solar System, so that the field of planetary science now has significant cross-over with the disciplines of geology and meteorology.
  
  Section::::Observation tools.
  
  Section::::Observation tools.:Telescopes.
  
raw_presuppositions: Telescopes can see, galaxies, planets and stars that are light years away.  The only way to see something thousands of light years away is to have a telescope that can see that far.
raw_corrections: Telescopes are not able to actually see the planets, but allow us to see things that proves the existence of other planets and stars.  Telescopes cannot see thousands of light years away, but light travels toward us from far away stars.