AY 101 Lecture Notes - Lecture 24: Ultraviolet, Ngc 891, Cosmic Dust
Document Summary
The h-r diagram is a graph of luminosity versus surface temperature for stars. It can be used to infer star sizes, and this in turn leads to the naming of stars in different regions as giants, supergiants, and dwarfs. The diagram brings to our attention four kinds of stars: Main sequence stars: stars which fall along a band from the upper left to the lower right. Red giants: large, cool stars above the lower part of the main sequence. Supergiants: very large stars near the top of the diagram, spanning the full range of star colors. White dwarfs: very small, hot stars comparable in size to the earth. Balance: the life cycle of any star is all about balance, that is, how to balance its mass against gravity. The key to a star"s stability is for fusion in the core to produce enough energy to hear the surrounding layers so that gravitational equilibrium, or exact balance, is achieved.
