Question: Last night the Moon rose exactly through the saddle of a nearby mountain, Gavilan Peak. I don’t think I’ve ever seen that happen before. How rare is that? — DH, New River, AZ
Answer: Well, you really have to be in the right place at the right time. If you’re willing to walk around a bit, you can catch it in this position a few times every year. But from any specific location, and at any specific time, and for a Full Moon, this only happens once every 18.4 years.
The Moon moves through the sky from east to west, tracking along a slightly different path each day. It’s orbit around the Earth is tilted by 5½°, and this tilt changes as Earth moves around the Sun. The combined effect of these motions is an 18.4 year cycle that’s been observed and recorded since the early days of astronomy.
This photo was taken a few months ago, a half-hour after sunset, from a point about a mile west of Gavilan Peak. The Full Moon is a difficult target for photographers because it is so incredibly bright. You can set the exposure properly for the Moon, but then the landscape will be underexposed and dark. If you set the exposure for the landscape, then the Moon is overexposed and washed out.
Any photo showing both the Moon and landscape is at best a compromise. But stay tuned … we’ll try for a better image in March of 2023, 18.4 years from this month’s event.