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The ‘O’ So Big Gobstoppers of the Universe!
26 July 2012

The Universe is like a pick n’ mix store when it comes to the variety of stars that it contains.

The colour of a star gives astronomers information about how heavy it is and the temperature of its surface. The hottest and heaviest stars are blue, while the coolest and lightest ones are red. (This is the opposite of how we use blue and red for hot and cold in everyday life, such as on water taps and weather reports.)

From the hottest to coolest, stars are put into one of the following groups: O, B, A, F, G, K and M. Our Sun is a middle of the range G-type star. As you can see, the order of these groups is not alphabetical.

But in English, there is an easy trick to remember the order: Just remember this phrase “Oh Be A Fine Girl/Guy, Kiss Me”. (Can you create an easy sentence to help remember the order in your language? Check out the activity at the bottom of the story.)

Recently, an international team of astronomers observed 71 O-type stars – the big ‘gobstoppers’ of the Universe’s sweet shop. From the sequence, you can see that these stars are scorching hot.

Until recently, astronomers thought that most O-type stars lived far away from their closest neighbours. However, the new research has shown that about 3 out of 4 of these stars live very close to another star. In fact, about 1 in 3 are so close that they will eventually merge into a single star! 

Get creative: We would love to see your suggestions for a simple sentence in your local language to help remember the order of the star groups, from hottest to coolest (O, B, A, F, G, K and M). Please send us your ideas to, along with your name (or the name of the school for group efforts), age and country.

More information

 This Space Scoop is based on an ESO Press Release.


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The ‘O’ So Big Gobstoppers of the Universe!
The ‘O’ So Big Gobstoppers of the Universe!


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