Today I looked up at the night sky and there was this wonderfully full moon, but it was sitting in the middle of a huge perfectly round disk opening into the heavens amidst the clouds. I wondered what the heck it was, thinking it might be the result of Earth-shadow.

It turns out this was a moon halo. The page says that the phenomenon is “familiar,” but I’ve never seen it in my life, and had I not looked up for no reason, I would have missed this one, too! By my hand measurement, it spanned 45° in diameter, which is a pretty big portion of the sky. Jupiter was also visible within the ring of the halo. Quite amazing.

Comments(1)

Great stuff, this comet. I only recall seeing one comet in person, back in the 1990′s. Must have been Hale-Bopp. Now that was a rare one.

Comet Lulin is arriving from the far reaches of the solar system on a nearly parabolic orbit—”it’s almost as if it comes from infinity and goes back out to infinity,” he said.

This must have been one of these initially stationary objects then. Speaking of orbits, unrelated to comets, these so-called halo orbits are pretty amazing. They are orbits around stationary points in the gravitational field of three bodies called Lagrange points. L1, L2, and L3 are pretty obvious and therefore not that cool, but L4 and L5 surprised me and they are even stable… The application of going to an unstable Lagrange point and redirecting routing with low energy is even nicer.

Comments(0)