Crescent Moonset 2

December 27, 2011 By: erik Category: Photos, Science, Timelapse

MoonsetThe moon just after sunset today was really gorgeous, hanging there in the sky next to Venus. The new moon was on Christmas Eve night, so Rudolph’s nose must have been extra important this year. After seeing the pretty Moon, up high in the sky, I told myself to go and look in an hour or two to see if I could catch it approach the horizon. Normally, I would never be capable of such a thing, but I actually did remember, and I caught it just as it was touching the horizon. Unfortunately, in the time it took me to set up my tripod, the tip of the moon went behind the hill on the horizon, but I still got nine shots in the time it took to set completely.
(more…)

How big is the Earth’s shadow on the Moon?

December 16, 2011 By: erik Category: Geeky, Math, Musings, Photos, Science

Earth's UmbraWhen I saw yesterday’s Astronomy Picture of the Day, I was fascinated by just how big the Earth’s shadow is on the Moon. When I made a comment to this effect on Facebook, my friend, Josh Grady, said, “It’d depend on the distance between the two, no?” Of course the size of a shadow depends on the distance to the object its cast upon, but I hadn’t considered that the distance from the Earth to the Moon varies, due to its slightly elliptical orbit around the Earth-Moon barycenter, by 42,840 km, causing it to appear 12% smaller at its apogee than at its perigee. This raised the question: What are the minimum and maximum sizes of the Earth’s shadow on the Moon?

To the geometrymobile!
(more…)