At 1.6 billion years old, this cluster of stars [
http://imagine.gsfc…] is beginning to show its age. NGC [
http://antwrp.gsfc.…] 7789 is an open or galactic star cluster [
http://www.seds.org…] about 8,000 light-years distant toward the constellation Cassiopeia [
http://www.seds.org…] and lies near the plane of our Milky Way [
http://antwrp.gsfc.…] 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.…] the hydrogen fuel in their cores. These have evolved from main sequence [
http://plabpc.csust…] stars like the sun into the gaggle of red giant stars apparent (with a reddish-yellow cast) in this lovely composite [
http://aibn47.astro…imagecolor.html#tri ] color image. Comparing computer models to observations of the red giants [
http://antwrp.gsfc.…] and main sequence stars astronomers can determine [
http://adsabs.harva…nph-bib_query?bibcod e=1998PASP..110.1318 G&db_key=AST&high=36 6dca0f3d29234 ] the mass and hence the age of the cluster stars just starting to "turn off" the main sequence [
http://ast.leeds.ac…] to become red giants.
Explanation
At 1.6 billion years old, this cluster of stars [
http://imagine.gsfc…] is beginning to show its age. NGC [
http://antwrp.gsfc.…] 7789 is an open or galactic star cluster [
http://www.seds.org…] about 8,000 light-years distant toward the constellation Cassiopeia [
http://www.seds.org…] and lies near the plane of our Milky Way [
http://antwrp.gsfc.…] 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.…] the hydrogen fuel in their cores. These have evolved from main sequence [
http://plabpc.csust…] stars like the sun into the gaggle of red giant stars apparent (with a reddish-yellow cast) in this lovely composite [
http://aibn47.astro…imagecolor.html#tri ] color image. Comparing computer models to observations of the red giants [
http://antwrp.gsfc.…] and main sequence stars astronomers can determine [
http://adsabs.harva…nph-bib_query?bibcod e=1998PASP..110.1318 G&db_key=AST&high=36 6dca0f3d29234 ] the mass and hence the age of the cluster stars just starting to "turn off" the main sequence [
http://ast.leeds.ac…] to become red giants.
Explanation
