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Stars are extremely large, extremely luminous bodies of gas at great distances. They are the most obvious features found in the universe.  They are principally composed of [[hydrogen]] that is undergoing nuclear [[fusion]] to become [[helium]]. Our Sun is the nearest star to Earth, at a distance averaging 93 million miles. The Earth orbits the Sun in a period of approximately 365.25 days, and this defines the [[year]]. The diameter of the Sun, which is a typical star, is about 870,000 miles and its power output is about 10²⁶ watts.

Stars are extremely large, extremely luminous bodies of gas at great distances. They are the most obvious features found in the universe.  They are principally composed of [[hydrogen]] that is undergoing nuclear [[fusion]] to become [[helium]]. Our Sun is the nearest star to Earth, at a distance averaging 93 million miles. The Earth orbits the Sun in a period of approximately 365.25 days, and this defines the [[year]]. The diameter of the Sun, which is a typical star, is about 870,000 miles and its power output is about 10²⁶ watts. The temperature inside the Sun is estimated to be in excess on ten million degrees, and this is hot enough for [[nuclear reactions]] to occur.

 

 

Some stars vary in brightness and are known as variable stars. The star [[Algol]] in the  constellation of Perseus can drop from its normal magnitude of 2.3 to magnitude 3.5. This is now known to be caused by a dim companion star orbiting Algol, which occasionally passes between Algol and the Earth, blocking some of the light. Other variable stars vary in brightness due to actual variations in the luminosity of the star itself. The most famous of these is delta Cepheus.

Stars are also often used as symbols on flags, such as the American [[flag]] (50 stars) and the flag of the [[European Union]] (12 stars).

Stars are also often used as symbols on flags, such as the American [[flag]] (50 stars) and the flag of the [[European Union]] (12 stars).

[[category:astronomy]]

[[category:astronomy]]