The July full moon, also known as the "Buck Moon" or "Thunder Moon," occurs just after midnight on Sunday (July 5), with the moon reaching full phase at 12:44 a.m. EDT (0444 GMT). A penumbral lunar eclipse starts just 14 minutes earlier, according to NASA's SkyCal, and the moon will be within a few degrees of Jupiter, the largest planet.
The subtle eclipse will be visible to observers from western Europe, Africa, most of North America, all of South America, and as far west as New Zealand. In parts of Africa and Europe the eclipse will occur at moonset, whereas in the westernmost regions such as New Zealand and Hawaii it will occur at moonrise. In the Americas the eclipse will be visible towards the middle of the night when the moon is highest in the sky, though this will vary with longitude.
A lunar eclipse occurs when the moon is on the opposite side of the Earth from the sun and passes through Earth's shadow. A penumbral eclipse is one in which the moon doesn't reach the darker part of the Earth's shadow; if you were standing on the moon you would see the Earth only partially eclipse the sun. Instead of getting completely dark, as during some partial and all total eclipses, the moon dims and sometimes looks a little bit more brown-gray than the usual white. In this case the moon will be approximately half-covered by the penumbra at maximum eclipse.
How to see the eclipse
According to Time And Date, in New York City the eclipse will start at 11:07 p.m. local time on Saturday (July 4), with the moon about 19.5 degrees above the south-southeastern horizon. Maximum eclipse occurs at 12:29 a.m. Sunday, and the eclipse ends at 1:52 a.m.
Those times will be an hour earlier in Chicago: 10:07 p.m. local time for the start of the eclipse, with mid-eclipse happening at 11:29 p.m. and the eclipse ending at 12:52 a.m. The biggest difference will be the moon's altitude; it will only be 13 degrees above the horizon. In Northern Hemisphere locales the shadow will appear to clip the "top" of the moon.
Skywatchers in the Southern Hemisphere will see the moon higher in the sky; the orientation of the shadow will also look different (as one is seeing it from a different angle on the surface of the Earth).
Those who catch it in Sao Paulo, Brazil, will see the eclipse start at 12:07 a.m. local time July 5, and the moon will be a full 89 degrees above the horizon, nearly directly overhead. Mid-eclipse is at 1:29 a.m. and the eclipse ends at 2:52 a.m. the shadow will appear to move across the right (eastern) side of the moon.
In southern Africa, the moon will be close to setting when the eclipse takes place on Sunday morning, beginning at 5:07 a.m. local time. Mid-eclipse occurs at 6:29 a.m. and the eclipse ends at 7:52 a.m., about a minute before sunrise. Moonset is at 8:03 a.m., so the eclipse occurs with the moon close to the horizon. The penumbral shadow, lacking a lot of contrast, will be difficult to see as the sky gets brighter.
While the eclipse is happening, observers will see the bright planet Jupiter near the moon. The moon and Jupiter will be in conjunction at 5:38 p.m. EDT (2138 GMT) on Sunday, meaning they will share the same celestial longitude as they make a close approach; the two objects will be just under 2 degrees apart, according to In-The-Sky.org. (For reference, your clenched fist held at arm's length measures about 10 degrees wide.)
As the actual conjunction will be during the day — the sun doesn't set in New York City until 8:30 p.m. local time — the moon will have moved somewhat farther away from Jupiter, but they will still appear relatively close. For skywatchers in New York City, Jupiter rises at 8:59 p.m. local time, and the moon rises at 9:16 p.m., with the moon appearing just below Jupiter. Both will be in the constellation Sagittarius. Joining the moon and Jupiter in the sky will be Saturn, which on Sunday will appear to the left of the moon and Jupiter, rising at 9:16 p.m. in New York.
The moon will make a close pass to the ringed planet on Monday (July 6), at 4:38 a.m. EDT (0838 GMT). Saturn will be about 20 degrees above the southwestern horizon, and the moon about three degrees lower. The two bodies will pass within two and a half degrees of each other, or about five times the apparent diameter of the full moon.
On the night of the full moon, Mars will also be visible. The Red Planet rises over New York City at 12:26 a.m. local time on Sunday, in the constellation Pisces, and stays visible in the sky until the morning (it reaches its highest altitude at 6:21 a.m., but the sun will have already risen by 5:31 a.m. local time.)
Venus will be a bright morning star, rising Sunday morning at 3:22 a.m. local time in New York City. A good exercise is to see how long the planet, which is at magnitude -4.4, stays visible as the sky brightens at dawn (magnitude is a measure of an object's brightness). Look for Venus in the east, in the constellation Taurus. Mercury will be effectively invisible as it rises only eight minutes before sunrise.
How the Buck Moon got its name
Native peoples in the Americas had various names for July's full moon; the names reflect that in the Northern Hemisphere it is summer and in the Southern Hemisphere it is winter.
"Traditionally, the full moon in July is called the Buck Moon because a buck’s antlers are in full growth mode at this time," according to the Old Farmer's Almanac. "This full moon was also known as the Thunder Moon because thunderstorms are so frequent during this month."
The name "Thunder Moon" was adapted from native peoples in what is now the eastern United States, where summer is thunderstorm season. However, the July full moon had other names. According to the Ontario Native Literacy Coalition the Ojibwe called it the Raspberry Moon, while Cree called it the Feather Molting Moon, as some birds start to molt in the summer.
The Māori of New Zealand used a lunar calendar called the maramataka which measured months between successive new moons. The June-to-July lunar month (which this year spans the new moons from June 21 to July 20) is called Hōngongoi, or "man is now extremely cold and kindes fires before which he basks." according to the Encyclopedia of New Zealand. This lunar month was, to the Māori, the second month of the year.
Related: Full moon names (and more) for 2020
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