shape of moon orbit around the sun

[makc]

clickety click

[Chris Peterson]

clickety click

And it's why the Earth could go away completely, and the Moon would continue merrily along in the same path it is currently in, just without those miniscule scallops.

[TNT]

Shouldn't its orbit be a wavy circle, considering that it is closer to the sun at times?

[Chris Peterson]

Shouldn't its orbit be a wavy circle, considering that it is closer to the sun at times?

I don't know. What's a "wavy circle"? <g>

[TNT]

Take a wavy line, for example, and put their ends together. Bingo! A wavy circle.

[BMAONE23]

clickety click

And it's why the Earth could go away completely, and the Moon would continue merrily along in the same path it is currently in, just without those miniscule scallops.

But isn't the Earth-Moon system following the Barycenter orbit around the Sun? And wouldn't the size of the orbit be directly affected by the loss of the mass of the Earth (more than 99% of the total combined mass)?
I don't believe that the Moon has sufficient mass/velocity to maintain a stable orbit at 1AU from the Sun without the Earth being part of the equation

[rstevenson]

... But isn't the Earth-Moon system following the Barycenter orbit around the Sun? And wouldn't the size of the orbit be directly affected by the loss of the mass of the Earth (more than 99% of the total combined mass)?
I don't believe that the Moon has sufficient mass/velocity to maintain a stable orbit at 1AU from the Sun without the Earth being part of the equation

I don't think mass is an issue. If we could materialize a baseball at the same orbital distance from the Sun as the Earth, and set it moving about the Sun at roughly the same orbital velocity as the Earth (~30km/sec), then that baseball would just keep orbiting the Sun quite happily.

If the Earth were to suddenly dematerialize, what would happen to the Moon's orbit around the Sun? It would depend a little on at what point in the Moon's orbit around the Earth this dematerialization occurred, but I think it's safe to say that the Moon would just continue to orbit the Sun in a slightly different elliptical orbit than it does now -- but without the "wavy" bits.

Rob

[Chris Peterson]

But isn't the Earth-Moon system following the Barycenter orbit around the Sun? And wouldn't the size of the orbit be directly affected by the loss of the mass of the Earth (more than 99% of the total combined mass)?
I don't believe that the Moon has sufficient mass/velocity to maintain a stable orbit at 1AU from the Sun without the Earth being part of the equation

The orbit of a small body around a massive central body is defined by radius and velocity. Mass is not a factor.

The Moon has an orbital velocity around the Earth of ~1 km/s, and an average orbital velocity around the Sun of ~30 km/s (same as the Earth, of course). So depending where it was on its orbit around the Earth when that planet disappeared, it could end up increasing or decreasing its orbital velocity around the Sun by 1 km/s, moving it either slightly closer or slightly farther from the Sun... but not much. Of course, it could also be in a point around Earth where there was no added velocity at all, in which case it would stay in exactly the same orbit- less the little scallops, which are the only evidence of the barycenter you speak of.

The Moon's orbit would be perfectly stable.

[bystander]

Earth Must Have Another Moon
Technology Review | Physics arXiv Blog | kfc | 2011 Dec 19

A study of the way our planet temporarily captures asteroids suggests that Earth should have at least one extra moon at any one time.

---

Back in 2006, the Catalina Sky Survey in Arizona noticed that a mysterious body had begun orbiting the Earth. This object had a spectrum that was remarkably similar to the titanium white paint used on Saturn V rocket stages and, indeed, a number of rocket stages are known to orbit the Sun close to Earth.

But this was not an object of ours. Instead, 2006 RH120, as it became known, turned out to be a tiny asteroid just a few metres across--a natural satellite like the Moon. It was captured by Earth's gravity in September 2006 and orbited us until June 2007 when it wandered off into the Solar System in search of a more interesting neighbour.

2006 RH120 was the first reliably documented example of a temporary moon.

But there should be many more examples, say Mikael Granvik and buddies at the University of Hawaii in Honolulu. Today these guys say they have modelled the way the Earth-Moon system captures these objects to understand how frequently we can expect to have additional moons and how long they should stay in orbit.

The answer is straightforward to state. "At any given time, there should be at least one natural Earth satellite of 1-meter diameter orbiting the Earth," say Granvik and co. These objects should hang around for about 10 months and make about three revolutions of the planet. That means Earth ought to have a metre-sized moon right now.

This is of more than academic interest. NASA has repeatedly said it is interested in sending humans to a near Earth asteroid. What better than to kick off with one that is in orbit here?

Finding a suitable candidate will be tricky though. Asteroids that are likely to become temporary satellites in the near future will be small and therefore hard to see. What's more, they will be subject to many forces pushing and pulling them so that predicting when and if they will ever be captured will be next to impossible.

But improved monitoring might help spot them when they get here, which might allow a launch to be planned in advance. Granvik and co conclude: "The scientific potential of being able to first remotely characterize a meteoroid and then visit and bring it back to Earth would be unprecedented."

The population of natural Earth satellites - Mikael Granvik, Jeremie Vaubaillon, Robert Jedicke

• arXiv.org > astro-ph > arXiv:1112.3781 > 16 Dec 2011

Earth’s Other Moons
Universe Today | Amy Shira Teitel | 2011 Dec 21

Earth Must Have Another Moon
Discovery News | via FoxNews.com/SciTech | 2011 Dec 22