In the night sky: Orion
In the night sky: Orion

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In the night sky: Orion

2.2.1 Types of star

Not all stars are the same and it is mainly their differences in mass that produce the wide variety of stars we see and many we can’t.

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MONICA GRADY:
When you look up at the sky you’d be forgiven for thinking that all stars are the same. But that’s far from the case. In fact there are lots of different types of stars - from brown dwarves to white supergiants - that can be categorised according to their mass and temperature - as in this Hertsprung-Russell diagram.
Red Dwarfs are small stars with temperatures cooler than that of the Sun. They are the most common stars in our galaxy and are less than half of the mass of the Sun. They burn slowly and so live for a long time relative to other star types. They are positioned on the lower main sequence on the Hertsprung-Russell diagram.
Red Giants are cooler than the Sun, so they have a red-orange tinge to the visible light they emit. Living up to their names, the largest red giants may be over 100 times the size of the Sun. Red giants are stars near the end of their life. They come above the main sequence on the Hertsprung- Russell diagram.
Stretching across the upper regions of the Hertsprung-Russell diagram are the Supergiants that cover a wide range of temperatures. These stars are truly enormous. Placed in the centre of our Solar System the largest of these, such as the red supergiant Betelgeuse in Orion, would engulf all the planets out to the orbit of Saturn.
Like Betelgeuse, Rigel in the Orion constellation is also a supergiant, but it is a blue-white supergiant. Supergiants are high mass stars near the end of their life. When a supergiant dies, it explodes as a supernova ...
... then shrinks to become a black hole.
There is a group of very faint but hot stars in the bottom left of the Hertsprung-Russell diagram. These are called White Dwarfs and are so faint that none is visible to the naked eye. They are very small and dense, formed when a main sequence star reaches the end of its life. White dwarf stars gradually cool over time until they no longer emit light.
The smallest, dimmest and coolest stars are Brown Dwarfs. They are at the bottom end of the Hertsprung-Russell diagram, at the lowest part of the main sequence. They are also known as ‘failed stars’ and are very difficult to detect as they do not have sufficient mass for nuclear fusion to occur.
There main variables in star formation are mass and temperature. It is these which produce the wide variety of stars we see and many we can't.
End transcript
 
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Red Dwarfs

Red Dwarfs are small stars with temperatures cooler than that of the Sun. They are the most common stars in our galaxy and are less than half of the mass of the Sun. They are positioned on the lower main sequence on the Hertsprung-Russell diagram.

Red Giants

Red Giants are cooler than the Sun, so they have a red–orange tinge to the visible light they emit. They may be over 100 times the size of the Sun and are stars near the end of their life. They come above the main sequence on the Hertsprung-Russell diagram.

Supergiants

Stretching across the upper regions of the Hertsprung-Russell diagram the Supergiants are truly enormous. Rigel is the brightest star in the Orion constellation and is a blue-white supergiant. Supergiants are high mass stars. Near the end of their life, when a supergiant dies, it explodes as a supernova, then shrinks to become a black hole.

White Dwarfs

White Dwarfs are faint but hot stars in the bottom left of the Hertsprung-Russell diagram. They are very small and dense, formed when a main sequence star reaches the end of its life. White dwarf stars gradually cool over time until they no longer emit light.

Brown Dwarfs

The smallest, dimmest and coolest stars are Brown Dwarfs. They appear at the lowest part of the main sequence on the Hertsprung-Russell diagram. They are also known as ‘failed stars’ and are very difficult to detect as they do not have sufficient mass for nuclear fusion to occur.

Explore star types for yourself.

Activity 2.2

Pick a star, this could be a star you’ve heard something about already or a group of stars such as brown dwarfs, and see what else you can find out about it.

For example, where is it on the Hertzsprung-Russell diagram that you looked at in The life of a star, approximately how old is it, roughly how far away is it, what constellation is it part of?

Write a short paragraph about what you found most interesting.

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Next, you’ll look at the reactions going on inside a star, and see how they affect how the star evolves.

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