question: We figure out the chemical compositions of stars by looking at their wavelengths, but wouldn't this be influenced by red shift?
comment: Yes, absolutely! But the spectra of the elements within stars aren't just single peaks, they are a series of peaks at very specific wavelengths and spacing. If the star's spectra is shifted (as they usually are) the characteristic pattern can still be detected and the amount of shift then used to calculate the relative movement of said star.
passages: "S" and "P" levels of hydrogen. By using lower frequencies than for optical transitions the Doppler broadening could be neglected (Doppler broadening is proportional to the frequency). The energy difference Lamb and Retherford found was a rise of about 1000 MHz of the "S" level above the "P" level.
   Real stars are not monochromatic, but emit a range of wavelengths approximating a black body distribution. It is not necessarily true that stars ahead of the observer would show a bluer color. This is because the whole spectral energy distribution is shifted. At the same time that visible light is blueshifted into invisible ultraviolet wavelengths, infrared light is blueshifted into the visible range. Precisely what changes in the colors one sees depends on the physiology of the human eye and on the spectral characteristics of the light sources being observed.
  
  Section::::Doppler effect on intensity.
   The motion of stellar objects can be determined by looking at their spectrum. Because of the Doppler effect, objects moving towards us are blueshifted, and objects moving away are redshifted. The wavelength of redshifted light is longer, appearing redder than the source. Conversely, the wavelength of blueshifted light is shorter, appearing bluer than the source light:
   The use of the Doppler effect for light in astronomy depends on our knowledge that the spectra of stars are not homogeneous. They exhibit absorption lines at well defined frequencies that are correlated with the energies required to excite electrons in various elements from one level to another. The Doppler effect is recognizable in the fact that the absorption lines are not always at the frequencies that are obtained from the spectrum of a stationary light source. Since blue light has a higher frequency than red light, the spectral lines of an approaching astronomical light source exhibit a blueshift and those of a receding astronomical light source exhibit a redshift.
   Unlike Cepheid variables, RR Lyrae variables do not follow a strict period-luminosity relationship at visual wavelengths, although they do in the infrared K band. They are normally analysed using a period-colour-relationship, for example using a Wesenheit function. In this way, they can be used as standard candles for distance measurements although there are difficulties with the effects of metallicity, faintness, and blending. The effect of blending can impact RR Lyrae variables sampled near the cores of globular clusters, which are so dense that in low-resolution observations multiple (unresolved) stars may appear as a single target. Thus the brightness measured for that seemingly single star (e.g., an RR Lyrae variable) is erroneously too bright, given those unresolved stars contributed to the brightness determined. Consequently, the computed distance is wrong, and certain researchers have argued that the blending effect can introduce a systematic uncertainty into the cosmic distance ladder, and may bias the estimated age of the Universe and the Hubble constant.
   RR Lyraes are similar to Cepheid variables but of lower metallicity (i.e. Population II) and much lower masses (about 0.6 to 0.8 time solar). They are core helium-burning giants that oscillate in one or both of their fundamental mode or first overtone. The oscillation are also driven by the kappa mechanism acting through the second ionization of helium. Many RR Lyraes, including RR Lyrae itself, show long period amplitude modulations, known as the Blazhko effect.
  
  Section::::Types of oscillators.:Delta Scuti and Gamma Doradus stars.
   The changes in slope in the synchrotron spectrum are parameterized with a "spectral index". The spectral index, α, over a given frequency range is simply the slope on a diagram of formula_3 vs. formula_4. (Of course for α to have real meaning the spectrum must be very nearly a straight line across the range in question.)
  
  Section::::A simple jet model.:Beaming equation.
  
  In the simple jet model of a single homogeneous sphere the observed luminosity is related to the intrinisic luminosity as
  
  where
   where "v" is recession velocity. Under special relativity, the two frequencies will also include an additional Lorentz factor redshift correction represented by the TDE formula:
  
  When we invert these relationships so that they relate to wavelengths rather than frequencies, "classical theory" predicts redshifted and blueshifted wavelength values of and , so if all three wavelengths (redshifted, blueshifted and original) are marked on a linear scale, according to classical theory the three marks should be perfectly evenly spaced.
   The traditional warm/cool association of color is reversed relative to the color temperature of a theoretical radiating black body; the hottest stars radiate blue (cool) light, and the coolest radiate red (warm) light.
  
  This contrast is further seen in the psychological associations of colors with the Doppler effect seen in astronomical objects. Traditional psychological associations, where warm colors are associated with advancing objects and cool colors with receding objects, are directly opposite those seen in astrophysics, where stars or galaxies moving towards our viewpoint on Earth are blueshifted (advancing) and stars or galaxies moving away from Earth are redshifted (receding).
   BULLET::::- In the very distant Universe (), LOFAR can search for the signature produced by the reionization of neutral hydrogen. This crucial phase change is predicted to occur at the epoch of the formation of the first stars and galaxies, marking the end of the so-called "dark ages". The redshift at which reionization is thought to occur will shift the 21 cm line of neutral hydrogen at 1420.40575 MHz into the LOFAR observing window. The frequency observed today is lower by a factor of 1/(z+1).
   Whether a scientific report describes TDE as being a redshift or blueshift depends on the particulars of the experimental arrangement being related. For example, Einstein's original description of the TDE in 1907 described an experimenter looking at the center (nearest point) of a beam of "canal rays" (a beam of positive ions that is created by certain types of gas-discharge tubes). According to special relativity, the moving ions' emitted frequency would be reduced by the Lorentz factor, so that the received frequency would be reduced (redshifted) by the same factor.
   BULLET::::- does the spectrum change with time? (for example, the star may turn hotter and cooler periodically)
  
  BULLET::::- changes in brightness may depend strongly on the part of the spectrum that is observed (for example, large variations in visible light but hardly any changes in the infrared)
  
  BULLET::::- if the wavelengths of spectral lines are shifted this points to movements (for example, a periodical swelling and shrinking of the star, or its rotation, or an expanding gas shell) (Doppler effect)
  
  BULLET::::- strong magnetic fields on the star betray themselves in the spectrum
   Studies performed in the 1980s and early 1990s produced confirmatory results:
  
  BULLET::::1. In 1989, Martin R. Croasdale reported finding a quantization of redshifts using a different sample of galaxies in increments of 72 km/s or Δ"z" = (where Δ"z" denotes shift in frequency expressed as a proportion of initial frequency).
  
  BULLET::::2. In 1990, Bruce Guthrie and William Napier reported finding a "possible periodicity" of the same magnitude for a slightly larger data set limited to bright spiral galaxies and excluding other types.
   In 1900, William W. Campbell and William H. Wright used the Mills spectrograph at the Lick Observatory to determine that this star has a variable radial velocity. The -day period of this variability as well as 0.2 magnitude changes in luminosity demonstrated in 1935 that the variability was intrinsic, rather than being the result of a spectroscopic binary. In 1938, a secondary period was discovered and a pulsation theory was proposed to model the variation. Since then, observation of Delta Scuti has shown that it pulsates in multiple discrete radial and non-radial modes. The strongest mode has a frequency of 59.731 μHz, the next strongest has a frequency of 61.936 μHz, and so forth, with a total of eight different frequency modes now modeled.
   Doppler imaging can also be made for changing chemical abundances across the stellar surface; these may not give rise to notches in the line profile since they can be brighter than the rest of the surface, instead producing a dip in the line profile.
  
  Section::::Zeeman-Doppler imaging.
  
  The Zeeman-Doppler imaging is a variant of the Doppler imaging technique, by using circular and linear polarization information to see the small shifts in wavelength and profile shapes that occur when a magnetic field is present.
  
  Section::::Binary stars.
   For relatively nearby galaxies (redshift "z" much less than unity), "v" and "D" will not have changed much, and "v" can be estimated using the formula formula_18 where "c" is the speed of light. This gives the empirical relation found by Hubble.
   The first detailed study of the spectrum of RU Cam showed that it changed during the brightness variations. From partway down the descending branch of the light curve to just after minimum brightness, the spectrum is class R with hydrogen absorption lines. The spectrum then develops hydrogen emission lines. For several days either side of maximum brightness, the spectrum becomes a relatively normal class K.
   The stars are very far away from us, so we only observe their one characteristic feature, their light. When this light is passed through a prism, it gives rise to a spectrum. Every star has its own spectrum and since each element has its own unique spectra, we can know a star's composition. We use thermal spectra of the stars to know their temperature. In 1920, when scientists were examining spectra of different stars, they found that some of the characteristic lines of the star spectrum was shifted towards the red end of the spectrum. The implications of this phenomenon was given by the Doppler effect, and it was clear that some stars were moving away from us. 
   A 2006 review by Bajan "et al." discovered weak effects of redshift periodization in data from the Local Group of galaxies and the Hercules Supercluster. They conclude that "galaxy redshift periodization is an effect which can really exist", but that the evidence is not well established pending study of larger databases.
  
  A 2007 absorption spectroscopic analysis of quasars by Ryabinkov "et al." observed a pattern of statistically significant alternating peaks and dips in the redshift range Δ"z" = 0.0 − 3.7, though they noted no statistical correlation between their findings and Karlsson's formula.
   Given that, in the case where the inertially moving source and receiver are geometrically at their nearest approach to each other, the receiver observes a blueshift, whereas in the case where the receiver "sees" the source as being at its closest point, the receiver observes a redshift, there obviously must exist a point where blueshift changes to a redshift. In Fig. 2, the signal travels perpendicularly to the receiver path and is blueshifted. In Fig. 3, the signal travels perpendicularly to the source path and is redshifted.
   However, where a previously absorbed line (first Lyman beta, ...) reaches Lyman alpha frequency, redshifting process stops and all hydrogen lines are strongly absorbed. But the stop is not perfect if there is energy at frequency shifted to Lyman beta frequency, which produces a slow redshift. Successive redshifts separated by Lyman absorptions generate many absorption lines, frequencies of which, deduced from absorption process, obey a law more dependable than Karlsson's formula.
   Delta Scuti variables are found roughly where the classical instability strip intersects the main sequence. They are typically A- to early F-type dwarfs and subgiants and the oscillation modes are low-order radial and non-radial pressure modes, with periods ranging from 0.25 to 8 hours and magnitude variations anywhere between. Like Cepheid variables, the oscillations are driven by the kappa mechanism acting on the second ionization of helium.
  
  SX Phoenicis variables are regarded as metal-poor relatives of Delta Scuti variables.
   This star belongs to a subset of RR Lyrae-type variables that show a characteristic behavior called the Blazhko effect, named after Russian astronomer Sergey Blazhko. This effect is observed as a periodic modulation of a variable star's pulsation strength or phase; sometimes both. It causes the light curve of RR Lyrae to change from cycle to cycle. As of 2009, the cause of this effect is not yet fully understood. The Blazhko period for RR Lyrae is .
  
  Section::::Description.
   § 5 Doppler provides imaginary examples of large and small frequency shifts for light from stars. Velocities are expressed in Meilen/s, and the light speed has a rounded value of 42000 Meilen/s. Doppler assumes that 458 THz (extreme red) and 727 THz (extreme violet) are the borders of the visible spectrum, that the spectrum emitted by stars lies exactly between these borders (except for the infrared stars of § 8), and that the colour of the light emitted by stars is white. 
  
  § 6 Doppler summarises: 
  
  BULLET::::- The natural colour of stars is white or a weak yellow.
   BULLET::::- A white star receding with progressive speed would successively turn to green, blue, violet, and invisible (ultraviolet).
  
  BULLET::::- A white star approaching with progressive speed would turn to yellow, orange, red, and invisible (infrared).
  
  Doppler wishes that his frequency shift theory will soon be tested by another method to determine the radial velocity of stars. He thinks, without reason, that a confirmation of his theory would imply that light is not a transverse but a longitudinal wave.
  
raw_presuppositions: We can not figure out the chemical c0mposition of stars due to red shift.
raw_corrections: We can still figure out the chemical composition of a star even if the spectra is red shifted.