Happy Apogee Day!


Moon at perigee (left) and apogee  — NASA

The nights are finally getting their voices back. I heard the wood frogs clucking for the first time yesterday evening while out observing with an astronomy group. We toured the galaxies, a few clusters and Saturn, the gem of the spring sky. Meanwhile the frogs sang music to the beat of their tiny, passionate hearts.

Now that the moon is past full, it rises quite late. Tonight you won’t see its jolly face until just after midnight. The moon’s orbit around the Earth is slightly elliptical or oval, rather than a perfect circle. This causes the moon’s distance from us to vary from about 214,000 miles to 244,000 miles during the course of every month.

Today the moon is furthest from Earth for the month of April, a situation called lunar apogee. Back on April 7, the moon was at perigee, or closest distance. If you look at the photo above, you’ll see there’s a significant size difference between these extremes. There’s also a difference in brightness.

Can you see this with your eye? It’s very difficult. Without a second moon nearby for comparison, it’s hard to recall if the moon tonight was smaller than what you remembered two weeks ago. But it does show up nicely when recorded with a camera.

Today is warm and sunny and gorgeous, reason enough to celebrate. But if you need an additional excuse to party, consider the (un)momentous occasion of lunar apogee.