Question

Astronomers can't travel to the stars. Telescopes do all the work.

How do we know that the spectra of a star is what we say it is? That is, how do we know those elements and molecules are there, even though the star is trillions of miles away?

What does a spectra that is shifted tell us about a star or galaxy?

Answer 1

Each element in the periodic table produce a spectra unique to that element. Hydrogen will not look like helium which will not look like carbon and so on. Astronomers measure the brightness of the light across the colors to create a plot of the spectrum. Absorption lines of a majority of the known chemical elements have now been identified in the spectra of the Sun and stars. If we see lines of iron in a star’s spectrum, for example, then we know immediately that the star must contain iron.

When spectrum lines appear shifted, it means the object is in motion. The spectrum can be used to identify the object’s velocity and whether it’s moving toward us or away.

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