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All I could find on the internet was about how stars vary in brightness depending on their distance to Earth, temperature, type of star...

But my question is, can a star can change its brightness.

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    $\begingroup$ Wikipedia has an extensive list of the mechanisms of variable stars. $\endgroup$ – pela Apr 10 '17 at 15:34
  • $\begingroup$ This is either a one word "yes" or requires coverage of the full range of variable stars, which is too broad. $\endgroup$ – James K Apr 10 '17 at 17:35
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    $\begingroup$ @JamesK Disagree, it is not too broad, as if the answer is not known to be "yes" you can just leave the question unanswered. That may be dissatisfying, but in this case the answer is "yes", so it doesn't matter. $\endgroup$ – called2voyage Apr 10 '17 at 19:22
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They can, and some do. These stars are called variable stars, because their luminosities as observed from Earth vary over time, often (though not always) in a regular period. Here are some broad categories:

  • Pulsating stars, where fluctuations lead to increases and decreases in size or temperature, which in turn produce changes in the star's brightness. Example: The oft-cited Cepheid variables.
  • Eclipsing binary stars involve two stars orbiting each other. When one passes between the other and Earth, the combined luminosity of the system appears to decrease, even though the stars' intrinsic luminosities are probably constant. Example: Algol.
  • So-called eruptive variables (often lumped together with cataclysmic variables, which are different) may have irregular outbursts caused by flares or other phenomena. Example: Luminous blue variables (LBVs).

The change in brightness and the length of the variations depend on the type of variable star in question. The luminosity can vary by anywhere from a fraction of a magnitude to many magnitudes. Likewise, the period (if there is one) can range from hours to years.

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Looking at the question longer-term, a star's brightness also changes as it evolves:

  • starting possibly with some brightness of its initial accretion disc,

  • then as nuclear burning begins it becomes a true star (check out the Hertzsprung Russell diagram showing stellar evolution)

  • later in its life, depending mainly on its mass it can either evolve into a near-dead dwarf, which will be increasingly dim

  • alternatively, heavier stars go supernova and become so bright as to briefly outshine galaxies before becoming dimmer again as neutron stars or black holes.

So to answer your question broadly - stars during their lifetimes do vary in brightness on a vast scale.

If interested further, I suggest you look up:

https://en.wikipedia.org/wiki/Hertzsprung%E2%80%93Russell_diagram

https://en.wikipedia.org/wiki/Stellar_evolution

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    $\begingroup$ +1, though this is probably not what the OP had in mind. $\endgroup$ – pela Apr 10 '17 at 20:21
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    $\begingroup$ Maybe not, but other readers might; and as it's worded I think the OP deserves to be shown that there's more to his question than he might have anticipated...? $\endgroup$ – iSeeker Apr 10 '17 at 22:36
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    $\begingroup$ Good point :) $\endgroup$ – pela Apr 11 '17 at 6:54
  • $\begingroup$ It's a great answer! i love getting lost on wikipedia $\endgroup$ – Dan Wears Prada Apr 11 '17 at 7:26

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