A partial lunar eclipse of the Harvest Moon Supermoon is coming. Here’s everything you need to know
On Tuesday, September 17th, the moon is full: the harvest moon.
The Harvest Moon is not exclusively a September event because the full moon that occurs closest to the autumn equinox is so nicknamed. Every few years, October (rather than September) is the site of this moon, which was once of vital importance to farmers. Before electricity and tractors with lights were used to bring in crops all night long, farmers relied on the light of the Harvest Moon to extend their workdays when fields were at their most productive.
The upcoming full moon will also be the last before the annular solar eclipse on October 2. This full moon will also feature a lunar eclipse, albeit a slight one, which can be seen as a prelude to the main event a fortnight later.
Beginning of the eclipse season
Both eclipses are of course related. A solar eclipse can only occur when the moon is at a node in its orbit. (The nodes are the two points where the moon’s orbit in the sky crosses the sun’s orbit, the ecliptic). During the solar eclipse, the moon crosses the ecliptic from north to south. But half an orbit earlier, at full moon, it crosses the opposite node. from south to northand encounters the shadow of the earth.
All of this is a beautiful example of how an “eclipse season” works. An eclipse season is when the sun is close enough (from our perspective here on Earth) to one of the lunar nodes to allow for an eclipse. During the season, which lasts just over a month, a lunar eclipse occurs at the full moon and a solar eclipse occurs at the new moon.
This will be almost like the lunar eclipse last March, although the Moon will not pass quite as far from the center of the Earth’s shadow and will manage to graze the dark umbra of the Earth. The umbra actually penetrates at most about 1/12 of the Moon’s diameter. Unlike the indistinct gray penumbra, the umbra is much darker and quite sharply outlined.
Visibility range
The region of visibility for this lunar eclipse includes much of North America (except Alaska and Hawaii) and all of South America (where the Moon will be directly overhead at maximum eclipse as seen from Sao Luis, Brazil). For those living on and near the Pacific coast of Washington, Oregon, and Northern California, the Moon will rise on the evening of September 17 and will already be in partial eclipse.
Conversely, the Moon will disappear from the western sky in much of Europe and Africa in the early hours of September 18, while in Finland, Ukraine, Turkey, Syria, Saudi Arabia, Ethiopia and Kenya the last remnants of its umbra will still be visible on the Moon’s western edge.
Only a slight solar eclipse
At maximum eclipse (September 18, 2:44 UTC), the umbra penetration will be only 8.7%, meaning that only the very edge of the Moon will be submerged in Earth’s dark umbra. For those who can observe this eclipse with binoculars or a telescope, it will probably be most interesting when the umbra brushes the northern edge of the dark, lava-filled lunar impact crater Plato at the time of greatest eclipse.
The entry into or exit from the penumbra is not visible. About 70% of the Moon’s diameter must enter the faint penumbra for it to be visible to most as a slight shadow or obscuration, about half an hour before first contact with the umbra (upper left part of the Moon) and about half an hour after last contact with the umbra (upper right part of the Moon).
With or without a telescope, the gentle curvature of the dark umbra on the moon’s disk – for the ancient Greeks it was a divine revelation – will serve as a nice reminder that our Earth is round.
Below is a timeline for the eclipse. Dashes indicate that the event will not be visible because the moon is below the horizon. An asterisk indicates that the calendar date is September 18.
| Event | Summertime | CDT | MDT | MDT |
|---|---|---|---|---|
| Moon enters the penumbra | 20:40 | 19:40 | — | — |
| Shades appear | 21:44 | 20:44 | 19:44 | — |
| Moon enters the umbra | 22:12 | 21:12 | 20:12 | — |
| Largest solar eclipse | 10:44 p.m. | 21:44 | 20:44 | 19:44 |
| Moon leaves Umbra | 11:16 p.m. | 22:16 | 21:16 | 20:16 |
| Shades disappear | 11:43 p.m. | 22:43 | 21:43 | 20:43 |
| Moon leaves penumbra | 00:47 hrs* | 11:47 p.m. | 10:47 p.m. | 21:47 |
Upcoming attractions
In 2025, the Moon will experience two total eclipses. The first will favor North America and will occur during the night hours of 13-14 March. Totality lasts 65 minutes. A second total solar eclipse will occur on 7 Septemberbut it will not be visible from the Americas. This late summer event will take place in the night sky over Europe, Africa and Asia and will last a total of 82 minutes.
The moon looks incredible through a telescope or binoculars. If you want to get a closer look at the moon’s many features during a lunar eclipse or any other time, be sure to check out our guides to the best telescopes and best binoculars.
And if you want to take photos of the moon yourself, we have tips for photographing the moon as well as guides to the best cameras for astrophotography and the best lenses for astrophotography.
Be sure to check out our Night Sky Tonight page and monthly skywatching calendar for more celestial events!
Joe Rao is a lecturer and visiting professor at the New York Hayden PlanetariumHe writes about astronomy for Journal “Natural History”The Farmers’ Almanac and other publications.
Editor’s note: If you capture a great image of the Moon during September’s partial lunar eclipse and want to share it with Space.com readers, send your photo(s), comments, and your name and location to [email protected].
