What colour are the coolest stars?

The coolest stars are red.

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What is meant by the 'luminosity' of a star?

Luminosity is the amount of energy emitted by a star per second.

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What does the Hertzsprung-Russell diagram show?

The Hertzsprung-Russell diagram shows the variation in a stars luminosity and temperature.


The x-axis is can also be colour or spectral class.

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What does the x-axis of the Hertzsprung-Russell diagram represent?

The x-axis represents the temperature of the stars.

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What does the y-axis of the Hertzsprung-Russell diagram represent?

The y-axis represents the luminosity of a star.

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What is the name given to the region labelled A?

Red supergiants

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What is the name given to the region labelled B?

Red giants

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What is the name given to the region labelled C?

White dwarfs

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What is the name given to the region labelled D?

Main Sequence

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What are the spectral classes of stars in order of decreasing temperature?

The spectral classes of stars, in order of decreasing temperature, are O, B, A, F, G, K, M.

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What do the spectral classes OBAFGKM represent?

The spectral classes represent the temperature and colour of stars.


O stars are the hottest and blue, while M stars are the coolest and red.

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