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Stars of NGC 206
| Title |
Stars of NGC 206 |
| Explanation |
Nestled within the dusty arms of the large spiral galaxy Andromeda [ http://www.seds.org/messier/m/m031.html ] (M31), the star cluster NGC 206 is one of the largest star forming regions known in our local group of galaxies. The beautiful bright blue stars of NGC 206 [ http://www.fera.com/M31.html ] betray its youth - but close, systematic studies of variable stars [ http://redfrog.norconnect.no/~poems/poems/00535.html ] in and around NGC 206 will also accurately reveal its distance. Astronomers are searching [ http://xxx.lanl.gov/abs/astro-ph/9902382 ] for variable stars in NGC 206, particularly pulsating stars known as Cepheids [ http://antwrp.gsfc.nasa.gov/apod/ap960110.html ] and eclipsing binary star [ http://astrosun.tn.cornell.edu/courses/astro201/bin_eclipse.htm ] systems. Distances for these types of stars can be effectively determined by following the periodic changes [ http://www.pbs.org/wgbh/aso/databank/entries/dp12le.html ] in their brightness and spectra. About 3 million light-years away, an accurately known distance to NGC 206 and thus M31 [ http://antwrp.gsfc.nasa.gov/apod/ap960406.html ] is critical to the larger understanding of galaxy formation, galaxy evolution, and ultimately the distance scale of the Universe [ http://antwrp.gsfc.nasa.gov/diamond_jubilee/debate96.html ]. |
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NGC 7789: Galactic Star Clus
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| Title |
NGC 7789: Galactic Star Cluster |
| Explanation |
At 1.6 billion years old, this cluster of stars [ http://imagine.gsfc.nasa.gov/docs/science/know_l2/stars.html ] is beginning to show its age. NGC [ http://antwrp.gsfc.nasa.gov/apod/ap990429.html ] 7789 is an open or galactic star cluster [ http://www.seds.org/messier/open.html ] about 8,000 light-years distant toward the constellation Cassiopeia [ http://www.seds.org/Maps/Stars_en/Fig/cassiopeia.html ] and lies near the plane of our Milky Way [ http://antwrp.gsfc.nasa.gov/apod/ap990224.html ] galaxy. All the stars in the cluster were likely born at the same time but the brighter and more massive ones have more rapidly exhausted [ http://antwrp.gsfc.nasa.gov/htmltest/gifcity/msblues.html ] the hydrogen fuel in their cores. These have evolved from main sequence [ http://plabpc.csustan.edu/astro/stars/main.htm ] stars like the sun into the gaggle of red giant stars apparent (with a reddish-yellow cast) in this lovely composite [ http://aibn47.astro.uni-bonn.de/~gallery/articles/ imagecolor.html#tri ] color image. Comparing computer models to observations of the red giants [ http://antwrp.gsfc.nasa.gov/apod/ap990312.html ] and main sequence stars astronomers can determine [ http://adsabs.harvard.edu/cgi-bin/ nph-bib_query?bibcode=1998PASP..110.1318G&db_key=AST&high=366dca0f3d29234 ] the mass and hence the age of the cluster stars just starting to "turn off" the main sequence [ http://ast.leeds.ac.uk/research/cmd.html ] to become red giants. |
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