How Do You Measure The Red Shift Of The Celestial Bodies?
Starlight appears bland to the eye. However, when we look at the wavelength distribution of the light (using a spectrometer), we see tiny bands of darker light (absorption bands) or brighter light (emission bands) that are caused by very specific chemical elements. Hydrogen is, of course, the most common culprit. The hydrogen bands have a very well known distribution (there are many bands and they are always placed exactly the same, relative to each other). On a graph, these peaks (or troughs) look like trees on a sloping plane, so astronomers have taken to call these patterns “forests”. A well known pattern is called the Lyman-alpha forest (Lyman is the name of a scientist who worked out the emission pattern of hydrogen). We look for this pattern in the starlight (or the overall galaxy’s light). Once we find it, we measure the wavelength of some very specific bands (we recognize individual “trees” in the forest). In a lab, we can measure the wavelength of the very same bands, with a c
