Stars

When we look up on a clear night we see a host of stars above us. They look like tiny points of light but stars are actually giant balls of glowing gas.

The Sagittarius Star Cloud

The Sagittarius Star Cloud: A Sky Full of Glittering Jewels
The Hubble Heritage Team (AURA/STScI/NASA)

The star that we are most familiar with is the Sun. In all aspects the Sun is a fairly average star, except that it is the one star we can see close-up.

The Sun is a mere 8 light minutes away, while most stars are hundreds and thousands of light years away, which is why they look so faint and small.

The closest star to our Sun is Alpha Centauri, which lies about 4.3 light years away. Alpha Centauri is actually a group of three stars, including the faint star Proxima Centauri, that are linked together by gravity. Over half the stars in the sky are double or triple star systems.

Stars vary in size, mass, brightness, age and colour. The largest stars are hundreds of times bigger than the Sun. The smallest stars (neutron stars) are some 10km across. Massive stars, more than 50 times the mass of the Sun, shine more brightly and have shorter lives than less massive stars. The temperature of a star is revealed by its colour. Hot stars, which are generally young, are blue while cool stars, which are generally old, are red.

Stars shine because of nuclear fusion reactions. The centre of a star is so hot that elements can fuse together to form new elements. The majority of a star's life is spent converting hydrogen into helium. This process produces lots of energy which is released as light to make the star shine and heat to stop the star from collapsing under gravity. In the core of our Sun millions of tonnes of hydrogen are fused together every second to form helium. All the elements around us, including those that are part of us, were originally formed in stars.

Comments (16)

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Natali 23 April, 2009 16:31
Are constellations in the same place all the time or do they move? why do they move? Do star constellations have a meanning?
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Discovery Centre 24 April, 2009 12:59
Even though everything in the Universe is in motion, constellations appear to move because we see them from a moving Earth. Star constellations have no intrinsic meaning, however different cultural groups around the world often invest spiritual meaning in star constellations.
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anna 25 September, 2009 13:34
this is good
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Naresh Sharma 9 October, 2009 23:53
Is it possible that at some point of time, Sun will start cooling down?
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Discovery Centre 16 October, 2009 11:07

The sun certainly is cooling down and experts say we only have about 4 billion years before it burns out completely! A NASA Astrophysicist recently answered a similar question and this website traces the lifecycle of a star like our sun. An extensive information sheet on the sun can be found on the NASA website.

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Cheyene 28 July, 2010 10:09
Why Are They Colourful But When We See Them They Are Just Black And White:)?
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Discovery Centre 8 August, 2010 14:57

Hi Cheyene,

A really good explanation of why we can't see the colour of stars can be found on the CSIRO website.

Hope this helps!

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MATTY DRAYTO 3 September, 2010 12:06
It was so cooooooooooooool. I wanna go again
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Alex 11 November, 2010 10:58
Is the Sun considered a star? Is Proxima Centuari Considered the second closest star to Earth
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Discovery Centre 13 November, 2010 13:37

Hi Alex,

Tes the Sun is a star and it is the nearest to the Earth at only 8 light minutes away.  That is, it only takes 8 minutes for the light of the Sun to reach the earth.  Proxima Centauri is the next closest star at 4.2 light years away, although it cannot be seen with the naked eye.  Proxima Centauri  is thought to be part of a triple system of Alpha Centauri.  Alpha Centauri is a binary system 4.3 light years away and can clearly be seen as the brightest of the two pointers which indicates the Southern Cross.  This means that Alpha Centauri is the nearest star that can be seen in the night sky.

Trust this helps!

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Ariel 17 November, 2010 15:08
hi, i am doing a earth progect and i was wondering if i could ask youthis question: what are the differences in day and night on different parts of the Earth
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Adma 15 December, 2010 10:21
what would a star taste like if it weren't so hot?
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jess 1 January, 2011 16:51
this is Awesome :0
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Russell 15 January, 2011 21:59
Hello there has been a very large light in the southern sky over melbourne over the past 2 months not everynight maybe every 4-5 days it looks the size of a golf ball could you tell me what it is please thank you,Russell
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Discovery Centre 19 January, 2011 15:07

Hi Russell, our staff at the Planetarium have said that without more precise details of time, direction, elevation etc it is hard to say what you have seen. They can say that it is not Venus as that planet is visible only in the early morning in the east before sunrise. You may be seeing Jupiter in the west after sunset but that just looks like a bright “star”. Its possible that you are seeing the moon as it approaches full moon but that won’t be in the south either.  

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Agnes 22 November, 2013 12:32
Hello! Great work on this website - plain English, informative and interesting...keep up the great work! Just a quick question to clarify (don't laugh now, laugh later!) does the above info mean that each star we see in the sky at night (I.e. each 'light' point in the sky, excepting our moon, any comets etc) is actually a sun? (Or cluster of suns or a galaxy if that far away that the light seems as though it's one point) I ask as I was under the impression that one could see - at specific times - out Venus, Jupiter etc. Does this mean that we don't see any planets outside our own solar system, and that the lights we see and call stars are all suns, with any orbiting planets not visible? Lastly, I read somewhere that a set up like our solar system is actually pretty rare...is this true? I.e. is it rare to have planets orbiting suns, (rare when comparing percentage wise to what we've discovered so far). Thank you and keep up the great work!
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