# What if there were no atmosphere

1. Mar 2, 2013

### 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...

2. Mar 2, 2013

### Staff: Mentor

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

3. Mar 2, 2013

### Staff: Mentor

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.]

4. Mar 2, 2013

### 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?

5. Mar 2, 2013

### Staff: Mentor

Oh, interesting.

6. Mar 2, 2013

### Staff: Mentor

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

7. Mar 2, 2013

### Staff: Mentor

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.

8. Mar 2, 2013

### Ezio3.1415

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

9. Mar 2, 2013

### 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...

10. Mar 2, 2013

### Staff: Mentor

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.

11. Mar 2, 2013

### 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.