A mere dusting, a slight shadow, falling on tonight’s full moon.
It is our very own shadow, cast by Mother Earth as her satellite swings through the faint outer shadow, which is called the penumbra. As such it is known as a penumbral eclipse.
Though the effect will be subtle, Space.com and other astronomy websites assure us that it is worth looking for. Those with the best view will be in Europe, Africa, the Americas and parts of Asia, the website PlanetSave says.
“Unusual shading on the southern half of the Moon should be fairly plain,” wrote Sky and Telescope. “Look for the penumbral shadow to move from (celestial) east to west across the disc. You might be able to detect lesser traces of penumbral shading for about 45 minutes before and after mid-eclipse.”
The eclipse is already under way, but it will be most visible at 7:50 p.m. eastern time. Eastern Turtle Island will have a good view, experts said. It is masking the Hunter’s Moon, which EarthSky.org explains is the full moon that falls after the Harvest Moon—the first full moon after the autumnal equinox in September.
Fall full moons are special, according to EarthSky.org.
“It’s characterized by a shorter-than-usual time between moonrises for several nights in a row around full moon,” EarthSky.org reports. “And you can see that, at each successive moonrise, the moon appears farther north on the horizon.”
This means that moonlight streams down from early evening till dawn for several nights in a row, as the moon rises a bit further north each night, a little closer to the previous moonrise than usual. Instead of rising 50 minutes later each night, it will rise 30 to 35 minutes later, EarthSky.org says—and up north in Inuit territory, it will actually be 15 to 20 minutes difference from the previous night.
Here, see Timeanddate.com's animation of what to look for.