I’m not talking about something in our solar system , im talking about astronomers claiming that a star billions of light years away is made only out of hydrogen and helium. How do they know that? And I’ve seen some other papers about planet temperatures and other things how do they know that too?
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When some material burns, it emits a light that has a “pattern” that can identify what elements that material is. This is a science called spectroscopy. By analyzing light from the stars, it is possible to figure out what elements that star is made of.
Stars are also classified by brightness, size etc. These form a fairly well defined pattern which allows scientists to estimate a range of distances a planet needs to be from that star in order for that planet to have a temperature similar to earth’s. This is not an exact prediction, of course, a lot of things have to be estimated.
Many things in astronomy work that way. By collecting a lot of observation from different stars, etc scientists build a model of how stars work and how the age over time. As they get learn how to build better telescopes and measuring equipment, they can measure things more precisely and refine their models of the cosmos.
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