a- 12 A A ? 1 u.abe x, x.A-e.A Background Part 2: Variable Stars Variable stars
ID: 292311 • Letter: A
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a- 12 A A ? 1 u.abe x, x.A-e.A Background Part 2: Variable Stars Variable stars are those that change their luminosity with time. They tend to be found in the Instability Strip on the HR Diagram. More information can be found at this Cosmos site (http://www.astronomy.swin.edu.au/cosmos//Instability+Strip); at the Wikipedia entries for the Instability Strip (http://en.wikipedia.org/wiki/lnstability_strip), Variable Stars (http://en.wikipedia.org/wiki/Variable_star), RR Lyrae Variables (http://en.wikipedia.org/wiki/RR Lyrae_variable) and related links as well as in your lecture textbook. Questions Part 2: Variable Stars 9. Are the ZZ Ceti variable stars also giant stars? If not, what type of star are they?Explanation / Answer
9. ZZ Ceti are a class of variable white dwarf star. Falling in the instability strip of the Hertzsprung-Russell diagram these stars pulsate with periods of minutes.Hertzsprung-Russell diagram which contains many different types of variable stars (RR Lyrae, Cepheid variable, W Virginis and ZZ Ceti stars all reside in the instability strip).
10.Harlow Shapley determined the position of the Sun in the galaxy by measuring the distances to 93 globular clusters of stars. He measured the apparent brightness and pulsation periods of RR Lyrae stars in the clusters.Astronomer Shapley used observations of these variable stars to make two important discoveries:
1) Globular clusters reside at great distances (1000s of pcs) from the Sun
2) By measuring the direction and distance of each cluster, he was able to determine their 3D distribution in space.
Thus, Globular Clusters map out a truly gigantic and roughly spherical volume of space about 20kpc across. RR Lyrae helped in this discovery because they are found in globular clusters.Shapley discovered that the universe was absolutely huge and spherical as well.
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