the lenth of day would...?

[nikhil311]

If there were no atmosphere,the lenth of the day would...
=>increase or decrease or remains unaffected ?

[Skids]

The length of your standard "day" is dictated by the speed that the Earth spins about its own axis of rotation.

[mibn2cweus]

Decrease; the Earth's atmosphere refracts sunlight above the horizon.

[JudgeJ]

I have to take issue with mibn2cweus. As skids says, the length of the day is dictated by the amount of time it takes the earth to rotate once about its axis.

The atmosphere may have an effect on the way we measure this period (in that it could effect the sighting of the sun or stars, which may be used as reference points), but this in itself does not alter the length of the day. The effect of friction between the earth and the atmosphere could have an effect on its speed of rotation; however, this would be extremely small.

The main effect of the speed of rotation of the earth (and hence the length of its day) is the “tidal effect” of the moon. The distortion of the earth’s shape (which effects the whole earth but is particularly evident in the oceans, as demonstrated by the twice-daily rise and fall of sea level) is gradually but very surely slowing the earth down. At the same time the orbit of the moon around the earth (currently 28 days) is speeding up.

Eventually the two will become tidally locked, with the same part of the earth always facing the moon. This happened to the moon some time ago (because the moon is much less massive than the earth) and that is why the same part of the moon always faces the earth.

[mibn2cweus]

JudgeJ, according to webster were both correct however technically were all wrong. Because the Earth revolves around the Sun in the same direction that it rotates it actually spins about one extra degree more than one full rotation in the period of one day.