BRAINCAKEThe Hertzsprung-Russell Diagram
The Hertzsprung-Russell (H-R) diagram is a graph of stars' luminosity against their surface temperature. Plotting many stars shows they fall into distinct groups.
Features of the axes:
• luminosity on the vertical axis, usually relative to the Sun (LSun = 1), on a logarithmic scale from about 10−4 to 106
• surface temperature on the horizontal axis, also logarithmic, decreasing from left to right (about 40 000 K down to 2500 K)
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Key terms in this lesson
- main sequence
- The stable, longest stage of a star's life in which it fuses hydrogen into helium in its core, forming a diagonal band on the Hertzsprung-Russell diagram.
- red giant
- A cool, highly luminous, greatly expanded star formed when a low-mass star's core contracts and hydrogen fuses in a shell around it.
- red supergiant
- A very large, extremely luminous, cool star formed when a high-mass star's outer layers swell as its core fuses progressively heavier elements.
- white dwarf
- The small, extremely dense, hot core left behind after a low-mass star sheds its outer layers, no longer undergoing fusion.
More in Space
- Wien's Law
- Luminosity and Intensity
- The Inverse Square Law for Intensity
- Estimating Stellar Radius and Temperature
- Formation of a Star
- Life Cycle of a Star
- White Dwarfs, Neutron Stars and Black Holes
- Trigonometric Parallax
All 18 lessons in Space · All Edexcel A-level Physics topics