# Is such an orbit possible?

## Main Question or Discussion Point

Hi,

Is to possible to have an orbit (say around the sun) where the planet (say the earth) would be slightly tilted (as it is) but would present the same hemisphere (say the north one) toward the sun all the time ?

It would mean that the earth would have to wobble?
Is that possible ?

It would also mean that there would be no seasons. The northern hemisphere would always be hot and the southern always cold. What would some repercussions of that be?

Thanks and sorry if this is a stupid question..

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Janus
Staff Emeritus
Gold Member
If I understand you right, you are suggesting an orbit where it would always be summer in one hemisphere and winter in the other, yet you still have a normal day/night cycle.

In that case, the answer is no, you can't.

russ_watters
Mentor
Hmm, well, you could have it always summer and always daytime. That's what happens when you get tidally locked.

But having a normal length day and a perpetual summer would require two-axis rotation.

If I understand you right, you are suggesting an orbit where it would always be summer in one hemisphere and winter in the other, yet you still have a normal day/night cycle.

In that case, the answer is no, you can't.

Yes, that's what I meant. I thought maybe some kind of wobbling could make it possible.

Wouldn't this be possible if earth's http://en.wikipedia.org/wiki/Precession_(astronomy)" [Broken] was 1 year long instead of the 26ish thousnad years it is now?

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Borek
Mentor
Slightly off topic, but very similar case - jus as seen from the Earth, not from the Sun.

Some wobbling necessary.

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Janus
Staff Emeritus
Gold Member
Slightly off topic, but very similar case - jus as seen from the Earth, not from the Sun.

Some wobbling necessary.
But the "wobble" here (known as libration), isn't due to any physical wobble of the Moon.

The side to side motion is due to the fact that the while the Moon rotates at a steady rate, its orbital speed varies due to the eccentricity of its orbit. Thus while the both the periods of the rotation and orbit are the same, during the course of the orbit, the rates don't matc at all times.

The nodding up and down motion is simply due to the fact that the moon's axis of rotation is slighty tilted when compared to the plane of its orbit. Thus at diffrent points of it orbit, it presents a little more of its Northern hemisphere and then it's Southern hemisphere. The axis doesn't shift, just the direction we view it from.

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Borek
Mentor
That's more or less what I was aiming at. Axis of rotation is not changing, but it is not perpendicular to the Earth orbit plane, so the rotating object - when observed from point moving around it - seems to be wobbling. This is simple geometry.

Even if technically it is Moon that revolves around the Earth

Cernole,

Yes this is the exact case with the planet Uranus where the planet is tipped on its axis to the degree that the poles always face in the direction of the sun. Thus one day equals a year on this strange world.

Regards

Alan

Janus
Staff Emeritus
Gold Member
Cernole,

Yes this is the exact case with the planet Uranus where the planet is tipped on its axis to the degree that the poles always face in the direction of the sun. Thus one day equals a year on this strange world.

Regards

Alan
No, it isnt. The poles of Uranus only line up with the Sun at two points of its orbit.

Slightly off topic, but very similar case - jus as seen from the Earth, not from the Sun.

Some wobbling necessary.

that is sequence is awesome, but its making me dizzy.

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