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Subject Calculating redshifts and blueshifts ~ A "How-To" site
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Original Message Found this interactive site and wanted to share...I had a dream last night about measuring redshift/blueshift. Of course I forget 'how' once I woke up so I went looking to figure out how to calculate redshifts on my own.

Sloan Digital Sky Survey/SkyServer
[link to skyserver.sdss.org]

This page shows you how to actually calculate redshifts, but the previous page will show you how to look up redshifts of twelve galaxies.


Astronomers learn an amazing number of things from analyzing spectra. In this section, you will focus on just one application: you will learn how to measure the redshift of a galaxy from its spectrum, and you will learn how to interpret and use the redshift.

Measuring Redshifts

Measuring a redshift or blueshift requires four steps:

1) find the spectrum of something (usually a galaxy) that shows spectral lines

2) from the pattern of lines, identify which line was created by which atom, ion, or molecule

3) measure the shift of any one of those lines with respect to its expected wavelength, as measured in a laboratory on Earth

4) use a formula that relates the observed shift to the object's velocity.

An example will help to show how this works. All spectral lines are created when electrons move around inside atoms. Hydrogen is the most common element in the universe, and it is often seen in galaxies. The spectrum of a hydrogen-containing region shows a pattern of spectral lines called the "Balmer series." The Balmer series is easy to reproduce in a classroom with a hydrogen discharge tube. The force that makes the gas glow is not the same as in galaxies, but the spectrum - the pattern of lines - is the same. Either from your own measurements in the classroom, or by looking the Balmer series up in a table, you know the rest wavelengths of Hydrogen's spectral lines to be as follows: (The wavelengths are given in Angstroms, equal to 100 trillionths of a meter)

And here is a PDF titled: The redshift and geometrical aspect of photons

I found it interesting that the author speaks about the possible redshift effect of dark matter field fluid. I'm only a few pages in so far...

[link to arxiv.org]


The cosmological redshift phenomenon can be described by the dark matter field fluid model, the results deduced from this model agree very well with the observations. The observed cosmological redshift of light depends on both the speed of the emitter and the distance between the emitter and the observer. If the emitter moves away from us, a redshift is observed. If the emitter moves towards us, whether a redshift, a blueshift or no shift is observed will depend on the speed vs. the distance. If the speed is in the range of c(exp[-&#946;D] 1) < v < 0, a redshift is observed; if the speed equals c(exp[-&#946;D] 1), no shift is observed; if the speed v less than c(exp[-&#946;D] 1), a blueshift is observed. A redshift will be always observed in all directions for any celestial objects as long as their distance from us is large enough. Therefore, many more redshifts than blueshifts should be observed for galaxies and supernovae, etc in the sky. This conclusion agrees with current observations. The estimated value of the redshift constant &#946; of the dark matter field fluid is in the range of 10-3 ~ 10-5 /Mpc. A large redshift value from a distant celestial object may not necessarily indicate that it has a large receding speed. Based on the redshift effect of dark matter field fluid, it is concluded that at least in time average all photons have the same geometry (size and shape) in all inertial reference frames and do not have length contraction effect.

just wanted to share :)
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