Star Classes Los Cumbres Observatory

Red Star, Blue Star Compared to a red star, a blue star always has A. more mass. B. larger radius. C. hotter temperature. D. all of the above.

Luminosity vs. Temperature Astronomers plot the luminosity of a star compared to its temperature. Absolute magnitude for luminosity Spectral type/class for temperature Sun

Hertzsprung-Russell Diagram The chart of luminosity vs. temperature is called the Hertzsprung-Russell diagram. This is the H-R diagram for hundreds of nearby stars.

Main Sequence Most stars are on a line called the main sequence. Hot stars brighter The size is related to temperature and luminosity. Hot = large radius Medium = medium radius Cool = small radius Sirius 1 solar radius

Giants Stars that are brighter than the main sequence are giants or supergiants. Large size More luminosity Betelgeuse is a red supergiant. Radius 1000 R Rigel supergiants Betelgeuse giants Aldebaran Capella

Dwarfs Stars that are dimmer than the main sequence are dwarfs. Small size Less luminosity Red dwarfs are on the main sequence. White dwarfs are hot and small. white dwarfs

Spectroscopic Parallax Parallax measurements of close stars determine the luminosity for placement on the H-R diagram. Distant stars similar to close ones Determine surface temp and spectral class of star. Place the star on the HR diagram where it should go. Read off the absolute luminosity from the diagram. Measure apparent luminosity and calculate distance.