Why do stars twinkle

A.� Their famous twinkle is the result of our earth's atmosphere, which, amongst other things, generates turbulence. As the atmosphere broils it bends, or refracts, the light from the star in different directions. This causes the star's image to change slightly in brightness and position, which our eyes pick up as a flicker, or twinkle.

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The scientific name for the twinkling of stars is stellar scintillation or astronomical scintillation.

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Q.� So, if I viewed a star from space it wouldn't twinkle

A.� No, stars would not appear to twinkle if we viewed them from outer space or from a planet that didn't have an atmosphere.

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This is why the Hubble telescope takes such amazing images: the lack of a distorting atmosphere allows a much better picture.

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Q.� Can planets twinkle

A.� No and it's one way of distinguishing them from stars.

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Q.� Why don't planets twinkle

A.� Stars are so far away that they're basically single points of light in the sky. As this single beam passes through our atmosphere and is bent by it, our eyes pick up this bending as a twinkle.

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However our eyes see light from planets differently. Planets, being much closer to earth, have a fixed size. This fixed size means that we see a large number of rays of light coming from the planet. Since there are lots of rays of light, rather than just one, as with a star, the image of the planet isn't completely at the mercy of our atmosphere and we see the planet as a stable object.

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Q.� Do we always see stars in the past rather than the present

A.� Yes, depending on how many light years away a star is, this is how old it is by the time we get to see it. No information of any kind can travel faster than the speed of light and so we'll never be able to see it 'now'.

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by Lisa Cardy