by Geoff Chester, USNO Public Affairs | 10 September 2024 The Moon, imaged 2024 February 20, from Alexandria, Virginia with an Explore Scientific AR102 10.2-cm (4-inch) f/6.5 refractor, 1.6X Antares 2-inch Barlow lens, and a ZWO ASI183MC CMOS imager The Moon waxes in the evening sky this week, gradually climbing northward along the ecliptic from the stars of Scorpius and ending the week in the company of the planet Saturn. Full Moon occurs on the 17th at 10:34 pm Eastern Daylight Time. This particular full Moon is something of a “trifecta”; not only is it the famed Harvest Moon, it also corresponds to one of the two closest lunar perigees for the year, and it will undergo a small partial eclipse by the shadow of the Earth. The Harvest Moon is perhaps the best-known of all of the monthly full Moon names. It gets its name due to the geometry of its orbital plane as it intersects with the eastern horizon at this time of year. From our location at mid-northern latitudes Luna’s orbit and the eastern horizon come together at a shallow angle around the time of the autumnal equinox. This shallow angle makes the Moon appear to rise at around the same time on the nights before and after the full phase. Normally Luna rises about 50 minutes later on successive evenings, but at the latitude of Washington, DC that interval is less than half an hour. The effect is accentuated as you move farther north. In Edinburgh, Scotland, the difference is just 10 minutes, while residents above the Arctic Circle actually see Luna rise earlier on successive nights. These close rising times around the time of full Moon allowed farmers of yesteryear to have a little bit of extra light to bring in their crops, hence the “Harvest Moon” moniker. For southern hemisphere residents the opposite is true. Their “harvest Moon won’t occur March 14, 2025. Lunar perigee occurs on the 18th about 10 hours before the full phase, a phenomenon that’s come to be called a “super Moon”. This is the first of two such close perigees for the year. The next one, in October, will be the year’s closest by just over 100 kilometers. The lunar eclipse on the 17th will be a small partial one as the Moon’s northern limb grazes the umbral shadow of the Earth. Between 10:00 pm and 11:16 pm EDT you will see a small circular notch drift across the top of Luna’s bright disc. Mid eclipse occurs at 10:44 pm, when about 9 percent of the disc will be obscured. You won’t have to wait too long to see the next total lunar eclipse, though; that will occur on March 14 next year. September 14th is the annual celebration of International Observe the Moon Night. Look on the website for events sponsored by astronomy clubs and science centers in your area. There are several such events in the Washington, DC vicinity. Many of these are sponsored by amateur astronomy clubs. It’s a great chance to find out about such groups in your location. If you have a telescope, set it up in your yard and invite the neighbors over. Most people who see Luna through a telescope for the first time never forget the experience! Now is the time to start looking for the bright glow of Venus in the evening twilight sky. To spot her, find a place with a low western horizon, then look due west about half an hour after sunset. Look about five degrees above the horizon with a pair of binoculars and you should see her pop into view. She will gradually gain a little altitude during the course of the week. By the beginning of October she should be much easier to see, and she will be a dazzling fixture in the evening sky throughout the winter months. Saturn is now visible in the sky all night long. Look for the planet’s yellow glow in the southeast as evening twilight gives way to darkness. He is slowly drifting westward among the faint stars of the constellation of Aquarius. His famous rings are now barely tilted to our line of sight, and in a small telescope the planet appears as a yellow globe with protruding spikes. By midnight you will begin to see the first of the bright constellations of winter rising in the east. Among them is the bright glow of Jupiter, cresting the horizon at around 11:30. The giant planet is still best viewed before dawn, when he will be near the meridian. East of Jupiter in the gathering morning twilight you should be able to spot the red-tinged planet Mars. He will continue to wend his way through the bright winter constellations as he heads toward opposition early next year.