Download HR diagram

The Hertzsprung - Russell Diagram
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The Hertzsprung-Russell diagram is an analytical tool for understanding the
properties of stars.
This diagram is a plot of stellar brightness (luminosity) versus stellar color
(temperature).
Brightness (luminosity) is plotted along the Y-axis; color (temperature)
along the X-axis.
The diagram is named for the two astronomers who created the first version
around 1912, uncovering fundamental relationships between the properties
of stars.
The observational HR diagram plots the brightness and colors of stars in
units of magnitudes. This version of the HR diagram is also frequently
termed the color-magnitude diagram.
The theoretical HR diagram plots the luminosity of stars expressed in solar
units, against stellar surface temperature, expressed using the Kelvin
temperature scale.
The X-axis is also labeled with the stellar spectral classifications.
Spectral class is defined by the type, number and strength of spectral lines
observed in a star’s optical spectrum.
Spectral classes are coded by letter: O, B, A, F, G, K, M.
Spectral class and color are defined by the star’s temperature.
An HR diagram, plotted using luminosity on the Y-axis and temperature on the
X-axis.
Stars, Revealed
What does the HR diagram reveal about the nature of stars ?
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Stars do not smoothly populate the HR diagram, nor are they randomly
distributed.
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The HR diagram contains many “regions”, where stars are more
concentrated:
 Main sequence: A thin band extending from the top left of the diagram to
the lower right. Dwarfs stars lie along the main sequence.
 Red giant region: Located towards the upper right of the diagram. Stars
located here are about 10 times larger than the Sun, and many time more
luminous.
 Supergiants: A band extending across the top of the HR diagram from
blue to red. These are extremely large and luminous stars.
 White dwarfs: A region in the lower left of the diagram. These are faint,
hot, very small stars.
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90% of stars lie along the main sequence, a consequence of the luminosityradius-temperature relationship.
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The Sun is classed as a G2 dwarf, and is located on the main sequence.
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Stars range in temperature from the hot O stars (up to 50,000 K) to the
relatively cool M stars (~3000 K).
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Stars range in luminosity from 10-4 to 104 L.
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Stars range in size from up to 500 R, labeled supergiants, to 0.01 R, the
smallest M dwarfs.
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The mass of a star defines its initial location on the HR diagram.
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As stars evolve, their luminosity and temperature change — they “move”
around the HR diagram.