The full moon of July, also called the "Buck Moon" or "Thunder Moon," will occur July 23 at 10:36 p.m. EDT (0236 GMT on July 24); the near-full moon will make a close pass of Saturn on July 24 and Jupiter on July 25.
Observers in New York City will see the almost-full moon set at about 4:46 a.m. local time on July 23, according to timeanddate.com, and it will rise that day at 8:32 p.m.
The full moon occurs when the moon is on the opposite side of the Earth from the sun. Earthbound observers see the moon reflect the sun's light, unless the moon's orbit carries it precisely within the Earth's shadow — a lunar eclipse.
The timing of a full moon depends on one's time zone, since a full moon is counted using the moon's position relative to the Earth's center rather than a given point on the surface.
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The moon's altitude in the sky, though, depends on one's latitude. The moon's orbit and the sun follow a path called the ecliptic, which is the plane of the Earth's orbit projected on the sky. The moon's orbit is slightly tilted by about 5 degrees to the ecliptic. That's why we don't get lunar eclipses every full moon and a solar eclipse every new moon.
However, it also means that during Northern Hemisphere summers, the full moons will be lower in the southern sky. The reverse is true in the Southern Hemisphere for the full moons in June, July and August — their winter — which will be higher up in the northern sky. The situation reverses in the Northern Hemisphere winters.
The full moon is so bright that through binoculars or a small telescope the glare can even require filters. There is no danger to one's eyes, but details can be harder to see because there are few visible shadows in the central part of the lunar disk — if an astronaut were there the sun would be directly overhead. Moon filters are available that can make some features stand out, or one can simply observe the moon a few days prior to or a few days after the full phase, when shadows make spotting surface features easier.
On July 24 at 12:38 p.m. EDT (1638 GMT) the just-past-full moon will be in conjunction with Saturn, according to In-The-Sky.org, passing just under 4 degrees (about 8 lunar diameters) south of the planet.
The moon will still be below the horizon, so the moment of closest approach won't be visible from the continental U.S., but in New York City, Saturn rises at 8:43 p.m. local time and the moon at 9:16 p.m. By about 10 p.m., Saturn will be above and to the right of the moon and Jupiter to the left of both; the three will form a flattened triangle and Saturn will be about 12 degrees above the southeastern horizon.
The moment of conjunction will be visible only from eastern Europe, Africa or Asia; for example, in Tokyo the conjunction will happen at 1:38 a.m. local time on July 25, just about an hour after the moon and Saturn reach their highest point in the sky (about 35 degrees above the southern horizon). For Australians, conjunction will be a bit later — 2:38 a.m. local time on July 25; Saturn will be 58 degrees high in the northwestern sky.
The moon passes Jupiter a day later. As seen from New York City the moon will pass just over 4 degrees to the south of Jupiter at 9:21 p.m. local time, but the moon doesn't rise until 9:52 p.m., so East Coast observers will again just miss the conjunction itself. Jupiter will rise first at 9:34 p.m., and by about 10:30 p.m. will be about 10 degrees above the horizon with the moon appearing about halfway between the horizon and the planet. Both bodies will be visible all night; getting as high as 36 degrees by 2:55 a.m. on July 26.
Here again it will be easier to see the conjunction as one moves east; in London the conjunction happens at 2:21 a.m. on July 26, so the moon and Jupiter will both be well above the horizon — by about 20 degrees — in the south-southwest by that point.
Other planets will be less spectacular around the full moon.
On July 23, the sun sets at 8:19 p.m. local time in New York and the planet Venus sets about an hour and a half later at 9:49 p.m. per heavens-above.com calculations, so the "evening star" should be visible just after sunset, though a bit tricky to spot as the sky will be somewhat light.
Mercury, meanwhile, will be a morning star, rising at 4:53 a.m. local time in New York City, just under an hour before sunrise. Here, too, the planet will be difficult to spot as the sky will be getting light. Be careful observing planets close to the sun, since looking through binoculars and accidentally focusing sunward is a sure way to permanently damage your vision. By sunrise Mercury will only be 8.6 degrees high in the northeast. But with a flat horizon (over the ocean, for example) and a very clear sky one can still catch it.
Mars will be in the west, setting at 9:32 p.m. local time in New York. Since it sets so soon after the sun does it will, like Venus, be very difficult if not impossible to see against the background of the still-lit sky.
Constellations on display
At the time of the July full moon, Northern Hemisphere summer constellations will be in full view all night, but the moon's brightness will wash out most fainter stars. The Summer Triangle — Deneb, Altair and Vega — will be approaching the zenith in the eastern sky towards midnight, and Antares, the brightest star in Scorpio, will also be reaching its highest point in the sky.
Looking roughly northwest at about 10:30 p.m. local time, the sky will be fully dark, and one of the first stars to be visible in that area is Arcturus, the brightest star in Boötes, the herdsman. If one turns a bit to the right (north), one can spot the Big Dipper, which will have its "bowl" facing upward. The two stars on the right side of the bowl will point to Polaris, the pole star. In the other direction, one can trace an arc along the handle and "arc to Arcturus" and then keep going to hit Spica, the brightest star in Virgo, low in the southwest.
Turning left (south), one will see Antares, the "heart" of Scorpio, the legendary creature that killed Orion the hunter (who appears in winter). Just above Scorpio one will see a tall, roughly rectangular shape made by some fainter stars; this is Ophiuchus, the healer who brought Orion back from the dead after Scorpio killed him. Ophiuchus is more difficult to see from urban areas, as the stars are fainter than Antares.
But if one turns to the left and upward, one comes to Altair, the brightest star in Aquila the Eagle, and the southernmost of the three stars of the Summer Triangle. Looking north (upwards) from Altair one will come to Deneb and Vega — Vega will be closer to the Zenith.
How the Buck Moon got its name
Related: Full moon names (and more) for 2021
Native peoples in the Americas had various names for July's full moon; the names reflect that in the Northern Hemisphere it is summer. "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 10 to July 9) is called Hōngongoi, or "man is now extremely cold and kindles 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.
The Chinese lunar calendar marks July's full moon as occurring in the sixth month, Héyuè, or Lotus Month, when the eponymous flowers bloom.
Muslims celebrate Eid-Al-Adha starting July 20, in a festival that lasts about four days, ending near the day of the full moon. Eid-Al-Adha honors Abraham's willingness to sacrifice his son to God as outlined in both the Bible and the Qu'ran.
For Jewish people, the midpoint of the lunation (full moon) is during the month of Av, and is the holiday of Tu B'Av which is a "holiday of love" and an auspicious time for weddings.
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