1. High temperature: Blue
Ordinary Stars
The Colors of Stars
Color of a star is determined by the peak wavelength of light emitted
The color of a star depends on its temperature:
Low temperature: Red
High temperature: Blue

2. Color & Temperature of Stars

3. Wien’s Displacement Law
Ordinary Stars
Wien’s Displacement Law
As the temperature of a star increases, the peak of its radiation is shifted toward shorter (blue) wavelengths
Stefan-Boltzmann Law
As the temperature of a star increases, the total energy output increases as the 4th power of the temperature

4. Ordinary Stars
Example: If one star has a temperature of 10,000 K and another a temperature of 5,000 K, how much more energy does the hotter star put out?
The first star is 2x hotter. That star puts out 24 or 16 times as much energy

5. Ordinary Stars Spectral Lines
Emission Spectra: Certain wavelengths of light appear brighter due to the presence of certain chemicals that are excited enough to glow
Absorption Spectra: Certain wavelengths are missing due to a cool gas absorbing those wavelengths

6. Spectral Lines

7. Ordinary Stars Spectral Types Different stars show different spectra
A classification scheme was soon developed
The different spectral types of stars are classified as:
O B A F G K M

8. Ordinary Stars Spectral Types Type O Star: 30,000 - 60,000 K
Color = Blue
Very short life Burn out quickly
Type B Star: 10, ,000 K
Example: Rigel (Orion)

9. Ordinary Stars Spectral Types Type A Star: 7,500 - 10,000 K
Color = Blue/White Strong H, Ca, Mg lines
Examples: Sirius (Canis major), Deneb (Cygnus)
Type F Star: 6, ,500 K
Color = Yellow
Example: Polaris

10. Ordinary Stars Spectral Types Type G Star: 5,000 - 6,000 K
Color = yellow Example: The Sun
Type K Star: 3, ,000 K
Color = Red Example: Aldebaran
Type M Star: < 3,500 K
Color = Red Example: Betelgeuse

11. Variable Stars Long Period Variables Cepheid Variables
RR Lyrae Variables

12. Binary Stars Pairs or groups of stars bound by gravity
Types of Binaries:
Visual
Spectroscopic
Eclipsing
Astrometric

13. Star Clusters:Open (Galactic) Clusters
Shape: Irregular, no specific shape
Where: Galactic disk
Types of Stars:
Population I
Age of Stars:
Young!

14. Star Clusters:Open (Galactic) Clusters
Open clusters contain a few dozen to a few hundred stars

15. Star Clusters: Globular Clusters
Shape:
Spherical
Where found:
Galactic Halo
Types of Stars:
Population II
Age of Stars:
Old

16. Star Clusters: Globular Clusters
Globular clusters contain 50,000 to 1 million stars