Changes

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.

==Research into the age of stars==

== 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:

 

 

 

 

 

 

 

==Old Universe View of Stars==

A team of astronomers from the University of Texas at Austin McDonald Observatory recently estimated the age of one of the oldest stars in the Milky Way, HE 1523-0901, at 13.2 billion years. They used radioactive decay dating techniques. This star is close to the estimated age of the universe, 13.7 billion years.  

A team of astronomers from the University of Texas at Austin McDonald Observatory recently estimated the age of one of the oldest stars in the Milky Way, HE 1523-0901, at 13.2 billion years. They used radioactive decay dating techniques. This star is close to the estimated age of the universe, 13.7 billion years.  

The team hope to gain new experimental data and important clues about the hypothesized creation and evolution of the chemical elements shortly after the Big Bang. <ref> http://www.astronomy.com/asy/default.aspx?c=a&id=5533 </ref>

The team hope to gain new experimental data and important clues about the hypothesized creation and evolution of the chemical elements shortly after the Big Bang. <ref> http://www.astronomy.com/asy/default.aspx?c=a&id=5533 </ref>

==References==

==References==