3 ms·
As pointed out by the other commenters, Cruithne doesn't orbit the Earth, but orbits the Sun with the in 1:1 resonance with the Earth. Its orbit is highly ellip
by quarterto 12y ago
As pointed out by the other commenters, Cruithne doesn't orbit the Earth, but orbits the Sun with the in 1:1 resonance with the Earth. Its orbit is highly elliptical: at perihelion it's closer than Mercury, and aphelion further than Mars. Much of the time it's actually on the other side of the Sun to us. Here's a couple of gifs of its orbit:
http://upload.wikimedia.org/wikipedia/commons/2/23/Orbits_of_Cruithne_and_Earth.gif http://upload.wikimedia.org/wikipedia/commons/2/23/Orbits_of...
http://upload.wikimedia.org/wikipedia/commons/c/c7/Horseshoe_orbit_of_Cruithne_from_the_perspective_of_Earth.gif http://upload.wikimedia.org/wikipedia/commons/c/c7/Horseshoe...
Note that its "orbit" around Earth actually takes 770 years!
- davegardner 12y agoSo I guess we can say with a high degree of confidence - "That's no moon".
- philh 12y agoMore on wikipedia: https://en.wikipedia.org/wiki/3753_Cruithne https://en.wikipedia.org/wiki/3753_Cruithne The yellow kidney bean orbit depicted only takes a year, but it doesn't actually form a loop, and the kidney bean moves gradually away from the Earth around the blue circle. When it goes almost all the way around, it's going to start going back in the opposite direction. 770 years is the time it takes for the yellow orbit to traverse the blue orbit once in each direction. Not only does it not orbit the earth in any physically meaningful sense - it doesn't even trace a shape that goes around the earth, which is annoying because I'm pretty sure I've told people that it did.
- dnautics 12y agoIs 1:1 really a resonance though? Any object with a similar semimajor axis will enjoy this orbital period, so it could just be a spatially defined coincidence.