Hertzsprung-Russell Diagram
The H-R Diagram plots each star on a graph and measures the star's brightness (luminosity) against its temperature (color). Temperature (K) •Measured in Kelvin (K) •Color of stars depends on their temperature •The coolest stars – red Hottest stars – blue •Temperature increases from right to left, which is different than every graph you’ve probably seen. Luminosity •The amount of energy (light) a star emits Brightness Apparent Magnitude Tells us how bright an object appears from Earth Absolute Magnitude The measure of a star’s brightness as if it were at a standard distance of exactly 10 parsecs (32.6 light years) from the observer. Spectral Class •Stars are classified by their spectra (the elements that they absorb) and their temperature. •There are seven main spectral types (O, B, A, F, G, K, and M) listed in order of decreasing temperature. Main Sequence •About 90 percent of the stars in the universe, including the sun •Ranges from high to low luminosity and high to low temperature •Color – ranges from red to blue •Spectral Class M-O Sun •Medium size star •Medium brightness and temperature •Color – yellow •Spectral Class G Red Giants •A red giant is a dying star. •Our own sun will turn into a red giant star, expanding to engulf the inner planets. •Color - reddish-orange hue •High luminosity/ low temperature •Spectral Class K-M Supergiants •They are the largest stars in the universe in terms of volume, although they are not the most massive. •Color – reddish orange/blue •High luminosity/low-high temperatures •Spectral Class K-M, B-A White Dwarfs •A small very dense star that is typically the size of a planet •Formed when a low-mass star has exhausted all its fuel •Color – white •Low luminosity/high temperature Spectral Class B, O, A Red Dwarfs •A small and relatively cool star on the main sequence •Color – red •Low luminosity/low temperature •Spectral Class – M Can you… 1.Can you interpret the H-R Diagram? 2.Can you use the H-R Diagram to explain how stars are classified? Comments are closed.
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Erik E. Mason
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