Celebrated in songs and folklore, the harvest moon is the best known of the year’s full moons. In 2020, the Northern Hemisphere’s harvest moon occurs on Thursday, October 1.
As the full moon closest to the autumnal equinox, it has a characteristic that make it stand out. It’s not that it rises at sunset — that’s true of all full moons. It’s that it’s close to sunset for a few days in a row.
On average, the moon rises 50 minutes later each day. But at this time of the year, the interval is much shorter — about 25 minutes a day, and even less at more northern latitudes. That means that, not just for one day but for a few days in a row, the moon is big and bright on the eastern horizon in the early evening. Hence the name: During the crucial harvest time, farmers got a little extra light to work by after the sun had gone down.
In the modern city, it means that for a few days the moon is rising at a time when people are more likely to be outside and see it at its most spectacular, big and orange and low on the horizon.
In the San Francisco Bay Area, Thursday’s official moonrise is around 7:15 p.m. — though, depending on the viewer’s proximity to eastern hills, it might take a couple minutes to come into view. On each successive night, as it starts waning, it will rise 25 to 30 minutes later.
This year, the harvest moon is also the first half of a “blue moon” pairing: There will be two full moons in October, the second on Halloween.
And there’s another celestial phenomenon going on right now: Mars is very noticeable in the night sky. The red planet appears as a very bright “star,” and because it also rises in the east at sunset, it will be traveling next to the full moon.
Mars appears particularly bright because it is approaching its Oct. 13 opposition, when the Earth is directly between Mars and the sun. Planets always appear brightest during opposition, and this is a particularly good one for Mars — it won’t be that bright again until 2035.
Peninsula residents will recognize the location: