Look sharp, Bay Area skygazers! The final supermoon of 2023 is almost upon us.
On the night of September 28-29, gaze skyward for the Harvest Moon which reaches its peak at 2:57am on Sept. 29. We’ll be able to enjoy a moon illumination of over 98% on the nights of Sept. 27-28, 28-29, and 29-30. According to Moon Phase Today, this is our last full supermoon until Aug. 19, 2024.
The term “Harvest Moon” refers to the Full Moon occurring closest to the autumn equinox, which this year falls on Sept. 23. According to NASA the term is an old European name that was first published in the 1706 Oxford English Dictionary, although the concept is echoed and honored in many cultures’ histories.
Native American tribes have referred to it as the “Autumn Moon” (Passamaquoddy), “After Harvest” (Kalapuya), “Nut Moon” (Cherokee), “Little Chestnut Moon” (Creek), and “Corn Maker Moon” (Abenaki).
Famously, China’s Autumn Moon Festival honors this full moon with traditional mooncake pastries and celebrations. Learn about San Francisco’s Autumn Moon Festival event here.
2023 was a big year for supermoons. In August we were treated to two supermoons in one month, the second of which was the “closest, biggest, and brightest full supermoon moon of 2023” according to the Old Farmer’s Almanac, appearing about 16% brighter and 14% bigger. A “Blue Moon” is the term used for the second Full Moon in a month, and the phenomenon won’t occur again until 2037 according to Forbes.
What is a supermoon?
A supermoon is a Full Moon that coincides with its perigee, or the closest orbital point to Earth, which is a distance of about 226,000 miles (363,300 km). The Moon appears 30% brighter and 17% larger than when at its apogee, or furthest point from Earth, which is a distance of about 251,000 miles (405,500 km).
Although “supermoon” isn’t an official astronomical term, it’s widely used to describe a moon that is within 90% of perigee. Supermoons only happen 3-4 times a year and are not always perceptible to the human eye, although they do usually result in higher ocean tides due to the Moon’s and Earth’s gravitational pull on each other.