What is Variable: Definition and 1000 Discussions

A variable star is a star whose brightness as seen from Earth (its apparent magnitude) fluctuates.
This variation may be caused by a change in emitted light or by something partly blocking the light, so variable stars are classified as either:

Intrinsic variables, whose luminosity actually changes; for example, because the star periodically swells and shrinks.
Extrinsic variables, whose apparent changes in brightness are due to changes in the amount of their light that can reach Earth; for example, because the star has an orbiting companion that sometimes eclipses it.Many, possibly most, stars have at least some variation in luminosity: the energy output of our Sun, for example, varies by about 0.1% over an 11-year solar cycle.

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  1. K

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  4. H

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  5. baby_1

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  6. T

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  7. T

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  8. G

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  10. T

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  12. I

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  13. N

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  15. F

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  16. P

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  17. R

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  18. O

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  22. W

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  24. F

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  25. N

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  29. I

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  33. F

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  36. H

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  43. I

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  49. C

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