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. M

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  4. D

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  5. R

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  6. S

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  7. M

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  13. C

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  14. S

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  15. QD311

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  16. A

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  17. M

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  18. M

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  19. M

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  20. T

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  21. M

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  22. I

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  23. G

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  24. J

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  25. K

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  30. F

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  36. O

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  37. S

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  38. Whovian

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  39. W

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  41. T

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  42. L

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  43. K

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  44. V

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  45. I

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  46. O

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  47. Spinnor

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  48. GreenGoblin

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  49. johann1301

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  50. J

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