H-R diagram

Ejnar Hertzsprung (left)
Born: 8th October 1873, Frederiksberg, near Copenhgen, Denmark
Died: 21st October 1967, Roskide, Dnmark
Henry Russell (right)
Born: 25th October 1877, Oyster Bay, New York, USA
Died: 18th February 1957, Princton, New Jersey, USA

• devised by Ejnar Hertzsprung and Henry Russell, the Hertzsprung-Russell (H-R) diagram is a graph to plot the temperature of stars against their brightness.
• the temperature of a star is indicated by its colour.
• cool stars are red or reddish-yellow.
• hot stars burn white or blue.
• medium sized stars form a diagonal band called the main sequence across the graph.
• the whiter and hotter a main sequence star is, the brighter it shine. White stars and blue-white stars are usually bigger and younger.
• the redder and cooler a star is, the dimmer it glows, Cool red stars tend to be smaller and older.
• gaint stars and white dwarf stars lie to either side of the main sequence star.
• the H-R diagram shows how bright each colour star should be – if the star actually looks dimmer, it must be further anyway (see below).

The brightest stars in the Orion constellation.

Rigel
-  the sixth brightest star in the sky and is a blue supergiant.
-  85,000 times brighter than our sun and is located 863 light-years away.
-  Rigel is a B-Type star that glows a blue/white color with a surface temperature of approximately 12,100K.

Betelgeuse
-  the eighth brightest star in the sky.
-  a red supergiant.
-  100,000 times brighter than our sun and is located approximately 643 light-years away.
-  completing the hourglass shape of Orion’s body are the stars Bellatrix and Saiph.

Bellatrix-
-  Orion’s third brightest star.
-  located above the Belt, to the right, west of Betelgeuse.

Saiph
-  the sixth brightest star in Orion.
-  Saiph is located below the Belt to the left.
-  Saiph is on the east side of Rigel.

 

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Did you know?

The H-R diagram shows the temperature and brightness of different types of stars.

On the left horizontal in blue – hotter / on the right horozontal in red – cooler.
On the top vertical is larger stars, the low vertical is smaller stars.

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