My understanding is that when an object moves away from you it increases the wavelength of the light presenting with a colour that is on the red side of the colourscale. Scientists also are able to determine what elements are present on planets based on the light it emits. How can they tell the difference?
I’m sorry for possibly using the incorrect terminology! Thanks in advance folks!
Edited the post because previously I had suggested that shorter wavelengths tended to the red side when in fact longer wavelengths tended to the red side of the colour spectrum.
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Exoplanet scientist here! This is exactly what I do every day.
Different chemicals absorb unique and VERY SPECIFIC wavelengths of light.
For example, the element calcium absorbs three lines at 849.8nm, 854.2nm and 866.2nm. Calcium is the only element with this feature.
No two chemicals share the same absorption lines, and we have huge databases of spectral lines absorbed by different chemicals.
This is like how every human has unique fingerprints, no two people have identical fingerprints, so it would be straightforward to compare a random fingerprint you find at a crime scene to a database of human fingerprints. This is how criminals are often caught.
This tells us about the chemicals in an exoplanet’s atmosphere.
You can compare the spectra you measure with big telescopes, to lists of absorption lines from databases, and look for matches.
Planets are always moving however, and movement will red- or blue-shift the light, meaning the absorbed lines measured by the telescope will be in the wrong place.
Thankfully, you can just factor in the additional info that your comparison to those line lists will have some constant offset due to the planet’s velocity.
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