![]() In fact, variable stars often provide the best means of studying the physical properties of individual stars - their variations turn them into "experimental laboratories" for stellar physics, and have given us many important clues as to what stars are and why they behave the way that they do.Įvery time someone observes a variable star, they're collecting evidence of how the star is behaving. Evidence about the physical properties of stars has also come from the study of variable stars. Another piece of evidence was the observational study of star clusters - groups of stars all born at the same time and place - and the eventual realization that the properties of star clusters differ depending upon how old they are. One was the understanding of the nuclear physics responsible for why stars shine, and the subsequent realization that stars have a large but finite source of fuel to create heat. There are many pieces of evidence that point toward our current understanding of stellar evolution. Since we can't observe stellar evolution over long timescales, how do we know it occurs? But this process can take millions or billions of years for a star, much longer than we can hope to observe directly. The process of change that a star undergoes during its lifetime is called stellar evolution. ![]() Their remains can then be taken up into new generations of stars, starting the process over again. One of the key concepts in astronomy is that stars change over time - they're born from clouds of interstellar gas and dust, they shine by their own light created through nuclear fusion of hydrogen in their cores, and eventually they run out of fuel and die, returning some of their mass back to interstellar space. Each one can tell us something about itself through its variability, and information that variable stars have provided has given us a better understanding of the larger picture. We have now discovered stars that vary on timescales from milliseconds to centuries. But variable stars do change on timescales that we can observe. Most things in the sky - stars, nebulae, and galaxies - don't appear to change at all during the course of a human lifetime. The universe is very large, stars and galaxies are very far away, and many changes occur on timescales far longer than we can see. Variable stars highlight an important fact about the heavens above us: the universe is always changing.
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