What if there were no atmosphere

[Ezio3.1415]

What would be the effect on day night period if there were no atmosphere? I mean would the days become longer or shorter? Why?PS:Admims,Trust me its not my homework...

 

[Dale]

The days and nights would be the same length, but there would be no twilight.

 

[russ_watters]

Depending on how precise you want to be, you'd get a few less minutes of the sun being up due to the elimination of atmospheric refraction. Roughly 1 solar diameter at the horizon equals about 4 extra minutes each at sunrise/sunset if the sun is setting vertically:
http://en.wikipedia.org/wiki/Atmospheric_refraction

[edit: er - I calculated 2 min, but thought I remembered it being 4.]

 

[Ezio3.1415]

The Earth's moment of inertia would be less,so angular velocity must increase to conserve the angular momentum... So day and night should be shorter...
Actually I asked the question,because many things can happen... I want to know what else are the factors?

 

[Dale]

Depending on how precise you want to be, you'd get a few less minutes of the sun being up due to the elimination of atmospheric refraction. Roughly 1 solar diameter at the horizon equals about 4 extra minutes each at sunrise/sunset:
http://en.wikipedia.org/wiki/Atmospheric_refraction

Oh, interesting.

 

[Dale]

The Earth's moment of inertia would be less,so angular velocity must increase to conserve the angular momentum...

No, its angular momentum would also be less, so there would be no change.

 

[russ_watters]

The Earth's moment of inertia would be less,so angular velocity must increase to conserve the angular momentum...

Conserve from what? We have to make up a story about how it lost its atmosphere or came to exist without one without changing its angular momentum. Now this is just idle speculation and storytelling.

 

[Ezio3.1415]

russ_waters: yeah that's a big effect... Do u think my logic is logical?

 

[Ezio3.1415]

now the Earth has to rotate with its atmosphere... So wouldn't the 'w' be a higher value if there's no atmosphere...

 

[Dale]

now the Earth has to rotate with its atmosphere... So wouldn't the 'w' be a higher value if there's no atmosphere...

No, why should it. The atmosphere has angular momentum. If it didn't exist then the Earth would have less angular momentum.

Now, if you are not just thinking of a "with vs without" scenario, but are rather thinking of a "before vs after" scenario, then you need to specify the process you are considering for removing the atmosphere.

 

[DrZoidberg]

If there was no atmosphere the oceans would evaporate. If the Earth had lost it's atmosphere 4 billion years ago, just as Mars did, it would now rotate at a higher speed since the tidal forces would be smaller.