What Are the Main Sequence, Red Giants, Supergiants, and White Dwarfs on an HR Diagram?

For IB Physics SL and HL: these are four major regions of a Hertzsprung and Russell (HR) diagram, classified by stellar luminosity and surface temperature. Main-sequence stars form a diagonal band, red giants occupy the upper right, supergiants lie across the top, and white dwarfs occupy the lower left.

How the HR Diagram Works

The vertical axis shows luminosity, which increases upwards. The horizontal axis shows surface temperature, but temperature decreases from left to right: hot blue stars are on the left, while cooler red stars are on the right.

A star's position can be explained using the Stefan and Boltzmann relationship:

L = 4\pi R^2\sigma T^4

What Are the Main Sequence, Red Giants, Supergiants, and White Dwarfs on an HR Diagram?

How the HR Diagram Works

A star's position can be explained using the Stefan and Boltzmann relationship:

L = 4\pi R^2\sigma T^4

Stellar region	Position and physical meaning
Main sequence	A diagonal band from the upper left to the lower right. These stars fuse hydrogen in their cores. Massive stars are hot and luminous; low-mass stars are cooler and less luminous. The Sun is a main-sequence star.
Red giants	Upper right. They have relatively cool surfaces but high luminosities because their radii are very large.
Supergiants	Across the top of the diagram. Their extremely large radii produce very high luminosities, whether their surfaces are hot or cool.
White dwarfs	Lower left. They are hot but dim because they have very small radii and therefore a small radiating surface area. They no longer undergo sustained core fusion.

What Are the Main Sequence, Red Giants, Supergiants, and White Dwarfs on an HR Diagram?

How the HR Diagram Works

MYP Subjects

What Are the Main Sequence, Red Giants, Supergiants, and White Dwarfs on an HR Diagram?

How the HR Diagram Works

Exam Technique