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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 Color & Temperature of Stars 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 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 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 Spectral Lines 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 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 - 30,000 K Color = Blue Example: Rigel (Orion) 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: 6,000 - 7,500 K Color = Yellow Ordinary Stars Spectral Types Type G Star: 5,000 - 6,000 K Color = yellow Example: The Sun Type K Star: 3,500 - 5,000 K Color = Red Example: Aldebaran Type M Star: < 3,500 K Color = Red Example: Betelgeuse Variable Stars Long Period Variables Cepheid RR Variables Lyrae Variables Binary Stars Pairs or groups of stars bound by gravity Types of Binaries: Visual Spectroscopic Eclipsing Astrometric Star Clusters:Open (Galactic) Clusters Shape: Irregular, no specific shape Where: Galactic disk Types of Stars: Population I Age of Stars: Young! Star Clusters:Open (Galactic) Clusters Open clusters contain a few dozen to a few hundred stars Star Clusters: Globular Clusters Shape: Spherical Where found: Galactic Halo Types of Stars: Population II Age of Stars: Old Star Clusters: Globular Clusters Globular clusters contain 50,000 to 1 million stars