1. Characteristics of Stars How are Stars classiﬁed
2. Color and Temperature• Looking at the night sky you can see some differences in the stars above.• Some are reddish, blue or yellow.• The star’s color reveals its surface temperature. The coolest stars - surface temperature of 3,200 degrees Celsius appear red. Yellow like our sun the surface temperature about 5,500 degrees Celsius. The hottest are bluish with surface temperatures over 20,000 degrees Celsius
3. Color and Temperature
4. Size• Looking at the sky most stars appear to be the same size• There are stars same size as the sun and some are much larger (giants&supergiants)• Most are smaller - White dwarfs are about the size of the Earth, and Neutron stars are about 20 km in size.
5. Star Sizes
6. Chemical Composition• Stars very in their chemical composition.• Most are about 73% hydrogen, 25% helium, and 2% other elements.• Astronomers use a spectrograph to determine the elements present in the star.• Gases in the atmosphere absorb some wavelengths of light, each absorbed wavelength is see as a dark band on the spectrum.• Each element has a unique spectral pattern.
7. Chemical Composition
8. Brightness• Stars differ in the amount of light they give off.• This depends on both size and temperature• Hotter stars tend to be brighter• Apparent brightness - measures its brightness as seen from Earth, does not tell how much light is given off by the star.• Absolute brightness - the brightness the star would have if it were at a standard distance from Earth. This is found using the apparent brightness and the distance from Earth.
10. Hertzsprung-Russell Diagram Surface temperatures are on the X-axis Absolute brightness is on the Y-axis The resulting points form a pattern this created the diagram now know as the H-R Diagram.