Aristotle. In the 4th century B.C., Aristotle of Stagira knew the Earth was round because of eclipses observed when Earth passed between the Moon and the Sun.
Intrinsic variability is due to physical changes such as eruptions or pulsations in the star itself, while extrinsic variability may be observed because of eclipses or the star's rotation.
Different types of intrinsic variables include: ...
  
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