Hertzsprung-Russell Diagram
Classifying Stars
Stars have been looked at and studied since ancient times. However, until 1911 scientists did not have a common way to study and classify stars. In 1911, Ejnar Hertzsprung used a graph to compare the brightness and temperature of stars. Hertzsprung was a Danish astonomer. Another astronomer, Henry Russell, from America also used a graph to compare and study stars. These astronomers ideas were combined into a tool now called the Hertzsprung-Russell diagram or H-R diagram. Astonomers use this tool to study stars today. The H-R diagram compares a star's surface temerature and absolute magnitude. Astronomers use this tool to study the life of a star and how it changes in temperature and brightness overtime.
Interpreting an H-R Diagram
An H-R diagram is fairly simple to read. The temperature of a star is listed along the bottom and the apparent magnitude is listed along the side. The brightest stars are located at the top of the H-R diagram. The dimmer a star is the lower it is located on the graph. The hottest stars are along the left of the graph and the coolest stars along the right. Most stars, as mentioned earlier, fall in the middle of the graph. These stars are the main sequence stars. Stars change their position on the H-R diagram throughout their lives.
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