Main sequenceMost stars, including the Sun, are on it. The band runs from the upper left (hot and bright) to the lower right (cool and dim).
The SunIt sits in the middle of the main sequence. Its surface temperature is about 5,780 K.
GiantsStars above the main sequence on the cool side. They are bright because they are big, not because they are hot.
SupergiantsThe largest, brightest stars, across the top of the chart.
White dwarfsSmall, hot stars that are dim because they are tiny. They sit in the lower left.
The two axes: 2 2
LuminosityHow much light a star gives off, increasing up the chart. It is sometimes shown as absolute magnitude.
TemperatureThe star's surface temperature, hottest at the LEFT, coolest at the right. It is sometimes shown as spectral class or color.
How this list was compiled: Read 2026-09-27. (1) Wikipedia, Hertzsprung-Russell diagram, https://en.wikipedia.org/wiki/Hertzsprung%E2%80%93Russell_diagram : a scatter plot of stars showing luminosity (or absolute magnitude) against temperature (or spectral type or colour index); the main sequence runs diagonally from the upper left (hot and bright) to the lower right (cooler and less bright); white dwarfs in the lower left; subgiants, giants and supergiants above the main sequence; the Sun on the main sequence at luminosity 1, temperature 5,780 K, spectral type G2V. (2) Wikipedia, Stellar classification, https://en.wikipedia.org/wiki/Stellar_classification : the classes O, B, A, F, G, K and M run from hottest to coolest, O stars blue; the mnemonic Oh Be A Fine Girl/Guy, Kiss Me. Licence: own work
The drawing: Drawn for this site by script, 2026-09-27. Own work, nothing traced. Licence: own work
How it works
An HR diagram worksheet: stars plotted by brightness and temperature, with each group to name. Start with the 5 star groups, then the two axes.
Read the full guide
Reading the axes
Luminosity, how much light a star gives off, goes up the side. Surface temperature goes along the bottom, but backwards: hottest at the left, coolest at the right.
The groups of stars
Most stars sit on the main sequence, the diagonal band, the Sun among them. Giants and supergiants sit above it: bright because they are huge. White dwarfs sit in the lower left: hot but dim because they are tiny.
The spectral classes run hottest to coolest as O, B, A, F, G, K, M: Oh Be A Fine Girl (or Guy), Kiss Me.
Questions and answers
What does an HR diagram show?
Stars plotted by how bright they are (luminosity) against how hot their surfaces are. Stars fall into groups on it: the main sequence, giants, supergiants and white dwarfs.
Why is temperature backwards on the HR diagram?
It follows the spectral classes, O, B, A, F, G, K and M, which run from the hottest stars to the coolest. So temperature falls from left to right.
Where is the Sun on the HR diagram?
On the main sequence, near the middle: a spectral type G2 star with a surface temperature of about 5,780 K.