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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. 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.

'''Stars''' are extremely large, 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.

==The Magnitude scale of brightness==

==The Magnitude scale of brightness==

The Greeks devised a rough and ready brightness scale for stars. The brightest stars were designated 'stars of the first magnitude', less bright stars were designated 'stars of the second magnitude', etc., down to stars of the sixth magnitude, which were barely visible to the naked eye. The magnitude scale is still in use, but modern telescopes and photometers have made it very much more exact and rigorous. A star of magnitude 1.0 is now 2.51188643 times as bright as a magnitude 2.0 star, which is 2.51188643 times as bright as a magnitude 3.0 star, and so on. This number has been chosen so that a magnitude 6.0 star is exactly 100 times as bright as a magnitude 1.0 star, i.e. 2.51188643 = 10^0.4.

The Greeks devised a rough and ready brightness scale for stars. The brightest stars were designated 'stars of the first magnitude', less bright stars were designated 'stars of the second magnitude', etc., down to stars of the sixth magnitude, which were barely visible to the naked eye. The magnitude scale is still in use, but modern telescopes and photometers have made it very much more exact and rigorous. A star of magnitude 1.0 is now 2.51188643 times as bright as a magnitude 2.0 star, which is 2.51188643 times as bright as a magnitude 3.0 star, and so on. This number has been chosen so that a magnitude 6.0 star is exactly 100 times as bright as a magnitude 1.0 star, i.e. 2.51188643 = 10^0.4.

==Variable stars==

==Variable stars==

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 time taken from one maximum brightness to the next one is called the '''period'''. The most famous of the variable stars is delta Cepheus, the first-found member of the [[Cepheid]] group of variable stars. In 1908 [[Henrietta Swan Leavitt]] noticed that the variable stars in the [[Magellenic Clouds]] (two nearby galaxies in the [[Local Group]]) had a relationship between their period and their apparent brightness. At that time galaxies outside our own (the [[Milky Way]]) had been discovered, but it was not possible to measure the distances to them. It was soon realised that the variable stars in the Magellenic Cloud were of the Cepheid type. Since Cepheid variables also occur in our [[galaxy]] it was possible measure their distances and thus convert (using the inverse square law) Leavitt's relationship between apparent brightness and period to one of actual brightness and period. Once this formula was discovered, it became possible to apply to Cepheids of unknown distance. By observing their periods, their actual brightness can be calculated and, by the inverse square law, their distance. Through observations of Cepheids in [[globular clusters]] (compact bunches of stars) in our galaxy it was shown that our galaxy is about 300,000 light-years in diameter.

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 time taken from one maximum brightness to the next one is called the '''period'''. The most famous of the variable stars is delta Cepheus, the first-found member of the [[Cepheid]] group of variable stars. In 1908 [[Henrietta Swan Leavitt]] noticed that the variable stars in the [[Magellenic Clouds]] (two nearby galaxies in the [[Local Group]]) had a relationship between their period and their apparent brightness. At that time galaxies outside our own (the [[Milky Way]]) had been discovered, but it was not possible to measure the distances to them. It was soon realised that the variable stars in the Magellenic Cloud were of the Cepheid type. Since Cepheid variables also occur in our [[galaxy]] it was possible measure their distances and thus convert (using the inverse square law) Leavitt's relationship between apparent brightness and period to one of actual brightness and period. Once this formula was discovered, it became possible to apply to Cepheids of unknown distance. By observing their periods, their actual brightness can be calculated and, by the inverse square law, their distance. Through observations of Cepheids in [[globular clusters]] (compact bunches of stars) in our galaxy it was shown that our galaxy is about 300,000 light-years in diameter.

== Young Earth Creationism View ==

== Young Earth Creationism View ==

[[Young earth creationism|Young earth creationist]] scientists assert that [[materialism|materialistic]] explanations of the origin of stars are errant and contra-evidence and reports of stars forming are invalid. <ref>http://www.icr.org/article/403/</ref><ref>http://www.answersingenesis.org/creation/v18/i2/stars.asp</ref><ref>http://www.creationscience.com/onlinebook/AstroPhysicalSciences21.html</ref><ref>http://www.answersingenesis.org/Docs/399.asp#55</ref><ref>http://www.answersingenesis.org/creation/v19/i1/feedback.asp</ref>  In addition, creationists cite the secular scientific literature in order to make the case that materialist explanations of star formation are inadequate:

[[Young earth creationism|Young earth creationist]] scientists assert that [[materialism|materialistic]] explanations of the origin of stars are errant and contra-evidence and reports of stars forming are invalid. <ref>http://www.icr.org/article/403/</ref><ref>http://www.answersingenesis.org/creation/v18/i2/stars.asp</ref><ref>http://www.creationscience.com/onlinebook/AstroPhysicalSciences21.html</ref><ref>http://www.answersingenesis.org/Docs/399.asp#55</ref><ref>http://www.answersingenesis.org/creation/v19/i1/feedback.asp</ref>  In addition, creationists cite the secular scientific literature in order to make the case that materialist explanations of star formation are inadequate: