Stars in the constellation of the Seven Sisters are just a tiny bit like a pair of scissors.
That’s because they’re each about a quarter the size of a human hair.
Seven Sisters, the seven brightest stars in the night sky, are all in the same part of the constellation, Alpha Centauri, and have different distances from us.
They’re all also different in brightness and colour.
For example, one is blue and the other is green.
Each of them has a distinctive red glow.
But what makes them so distinct?
These stars are called sisters.
“They’re really pretty,” says Pauline Dennison, a lecturer in astronomy at Stony Brook University.
“There’s a big overlap between the colours of their light.”
And the different colours are a key way the sisters are named.
“I’ve been told they are named after the fact that they all have the same number of colours,” she says.
“But that’s just because they are sisters, not because they look alike.”
It’s not just the colours that make them distinctive.
As well as being bright, they are also relatively large.
“In the same way that a human hand is only three centimetres in diameter, a human body is only two centimetre wide,” says Professor Dennion.
“So the number of stars in each of those is really small.”
That means that the sisters can be seen at a distance.
So you can get a better idea of their size by looking at the stars that they are closest to.
“The brightest ones are the closest to us, so that means they’re closest to the Earth,” says Denniks.
But stars are not all the same colour.
“A star that’s bright red, for example, might not be quite as bright as the brightest star in the sky,” she explains.
And if the star is very close to us then it might not look like it’s a red star at all.
It might be a white star.
So the colours are important to the sisters.
But how do they look in the daytime?
“I would say they are very common in the skies,” says Prof Dennisons.
“You will see them very easily in the evening sky, because the sky is very dim and there are no stars in it.”
So what are the best ways to look for them?
The best time to look is when the sky becomes clear.
“If you can see the stars well before dawn, then it’s time to start looking,” says the lecturer.
And to look at them you should also be looking at Polaris, the brightest of the three constellations.
It’s the northern hemisphere’s brightest star.
And it is a red one, meaning that it’s blue in colour.
If you can’t see Polaris well enough, you should look at the Southern Cross.
“It’s the brightest cross of the sky and you should be able to see it very easily,” says Dr Dennon.
You might also want to look up at the Pleiades or Ursa Major stars, which are the two brightest stars.
“And look at Orion, the North Star,” she adds.
The brightest stars can also be seen very close by.
The Orion Nebula, for instance, is one of the brightest objects in the Universe, so it’s likely to be easy to spot in the Northern Hemisphere.
But it’s not the brightest stars that you should care about most.
“Look for them when the stars are quite low in the northern sky,” says Dame Dennings.
But don’t worry too much about looking at them too much.
“For most people it won’t be a problem,” she suggests.
“Especially in the winter.”
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Find out more The stars in this article are: A star that has a red colour.
Blue stars are close to the Sun and the brightest in the Southern Hemisphere.