The July full moon, also known as the Buck Moon, occurs on July 21, at 6:17 a.m. EDT (1017 GMT), according to the U.S. Naval Observatory. The full moon shares the evening sky with Mercury, which will be at its greatest apparent distance from the sun that day.
Moonset is at 5:29 a.m. that day in New York City, but farther south the moment of full phase occurs before then. For example, in Charleston, South Carolina, moonset is at 6:20 a.m., and in Miami, it is at 6:40 a.m.
Full moons happen when the moon is on the opposite side of the sun from Earth and is fully illuminated. For an astronaut standing on the moon (on the center part of the disk as seen from Earth), it would be noon; the sun would be directly overhead at the moon's equator, and as high as it ever gets in the sky as one moves north or south.
The timing of lunar phases depends on one's time zone since the phase depends on the moon's position rather than that of the observer. So, while in the U.S. Northeast, the moon sets before it becomes officially full, as one travels westwards the time moves back. In Los Angeles, for example, the full moon is July 21 at 3:17 a.m. local time, well before moonset at 5:58 a.m. In Hawaii (which does not observe daylight savings time), the moon is full at 12:17 a.m. on July 21. In cities such as Tokyo, the full moon is at 7:17 p.m. on July 21, and moonrise is at 7:10 p.m. local time.
Related: The moon: Everything you need to know about Earth's companion
One thing that distinguishes summertime full moons in the Northern Hemisphere is that they tend to be low in the sky and often look yellowish because the reflected light from the moon has to go through more of Earth's atmosphere, which tends to scatter shorter (bluer) wavelengths.
The moon, like planets, travels near the ecliptic, the path the sun describes as it moves against the background stars. In the summer, the moon is on the opposite side of the sky from the sun, which is on the part of the ecliptic that is higher in the Northern Hemisphere. This difference is a function of Earth's axial tilt and is why days are longer and in the summer months.
The moon, however, is in the part of the sky the sun would be in during winter months, so it never gets very far above the horizon. The situation is reversed in the Southern Hemisphere, where it is winter (and the full moon is correspondingly high in the sky).
Planets visible during the Buck Moon
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On the night of the full moon, just after sunset, which is at 8:21 p.m. in New York, one will be able to see Mercury, which reaches its greatest eastern elongation — the maximum apparent distance from the sun — at 11:37 p.m. EDT. The planet sets at 9:34 p.m., so it won't be very high in the sky; it will only be 5 degrees above the western horizon by 9 p.m. (Your clenched fist held at arm's length covers about 10 degrees of sky.) But careful observations after sunset might allow you to see it before then. Do not try to use any optical aid to see it until the sun is below the horizon, however; observing any objects close to the sun is dangerous because even split-second exposure to sunlight through binoculars or a telephoto lens can cause permanent damage to your retinas.
Observing Mercury is a bit easier as one moves closer to the equator; the sun sets slightly earlier, and the angle Mercury makes in its journey across the sky is steeper with respect to the horizon. From Miami, for example, sunset is at 8:12 p.m. and Mercury is 18 degrees above the horizon; 30 minutes after sunset, it is still 11 degrees high and easier to see.
From more equatorial locales, such as Cartagena, Colombia, the sun sets earlier still, at 6:27 p.m., and by 7 p.m. Mercury is 15 degrees above the western horizon; the planet sets in Cartagena at 8:07 p.m. local time.
In the Southern Hemisphere, it is winter and the sun sets early; in Santiago, Chile, sunset is at 5:57 p.m. local time and the sky is getting dark by 6:30 p.m. when Mercury will still be 18 degrees above the west-northwestern horizon.
Venus will still be lost in the solar glare; it will emerge in August and be a bright "evening star" this autumn. As one moves south, Venus will be just visible after the sun goes down, though still a very difficult target; even in Cartagena, it is no more than 12 degrees above the horizon by sunset, and by 7 p.m. it is 6 degrees high; to catch it one will need a clear sky and flat horizon with no obstructions.
In the evening on July 21, one will see Saturn follow the moon as it climbs higher in the sky; the ringed planet comes up at 10:36 p.m. local time in New York City (the local rising time will be similar in cities such as Chicago, Denver and Sacramento). Saturn will be at its highest by about 4:17 a.m. when it is about 43 degrees above the southern horizon.
Mars is an after-midnight planet, rising in the wee hours of July 22 at 1:34 a.m. in New York. Jupiter follows at 2:15 a.m. By about 4 a.m., the two planets will form a rough triangle with Aldebaran, the brightest star in Taurus, the Bull, low in the Eastern sky. Mars will be distinct because of its reddish color, above and to the right of Jupiter, with Aldebaran slightly below and to the right of Jupiter. If the sky is clear and you're away from city lights, you might be able to spot the Pleiades, a small open cluster of stars; the full moon might make it harder to see, however, as it washes out many fainter objects in the night sky. One can look upward from and to the left of Mars to find it.
In the Southern Hemisphere, Saturn, Mars and Jupiter will rise in the same order, but, rather than being toward the southern side of the sky, they will be to the north. From Melbourne, Australia, for example, where the full moon occurs July 21 at 8:17 p.m. local time, sunset is at 5:23 p.m. Saturn rises at 9:22 p.m. and reaches a maximum altitude of about 58 degrees above the northern horizon by 3:43 a.m. local time.
Mars rises at 3:16 a.m. in Melbourne and is followed by Jupiter at 4:13 a.m. As in the Northern Hemisphere, the planets and Aldebaran form a rough triangle, but this time it is facing the other way; Mars will be above and to the left of Jupiter and Aldebaran above it and to the right. The Pleiades will be below and to the slight left of Mars.
Constellations visible during the Buck Moon
In July, the summer constellations are ascendant; from mid-northern latitudes, the three stars of the Summer Triangle, Vega, Deneb, and Altair, are high in the east. Vega rises first, followed by Deneb, and Vega is the highest in the sky; it is 73 degrees high in the east by 10 p.m. Deneb will be closer to the horizon, to the left of Vega (eastward) and Altair will be below them both, towards the south. The three stars form a right triangle with Deneb at the 90-degree corner.
Vega is the brightest star in Lyra, the Lyre, the instrument of Orpheus. Deneb is the tail of Cygnus the Swan, and Altair is the eye of Aquila, the Eagle.
Cygnus has its own asterism, the Northern Cross, made of five medium-bright stars that mark the Swan's wings and head. The "head" star is called Albireo, or Beta Cygni, and the star at the junction of the cross is Sadr, or Gamma Cygni.
Looking to the left of the Summer Triangle and facing north, at 10 p.m. the Big Dipper is to the left (west) of the celestial pole and about a third of the way below it. The Dipper faces downward, with the stars of the bowl toward the horizon and the handle pointing up. Using the "pointers" on the bowl (these will be the stars closest to the horizon) one can find Polaris, the pole star. On the other side of Polaris is a W-shaped constellation in the northeast and about a third of the way up from the horizon to the zenith. This is Cassiopeia, the legendary queen of Ethiopia and mother of Andromeda.
Going back to the Big Dipper — itself an asterism that is part of the much larger Ursa Major, the Great Bear — one can use the handle to "arc to Arcturus" the brightest star in Boötes, the Herdsman. Arcturus is recognizable because it is a slightly orange color. Above Arcturus one can sometimes spot a circle of fainter stars; this is usually drawn as Bootes' head. To the right is a bright curve of stars that is the Northern Crown, the Corona Borealis.
If one turns exactly opposite from Polaris and looks due south, by 10 p.m. one can see a bright reddish star about 22 degrees above the horizon and a bit to the west. This is Antares, the heart of Scorpius, the Scorpion. Even with the full moon nearby (just above the southeastern horizon) it is easy to see; to the right of Antares one can see three stars in a roughly vertical line that are the Scorpion's claws, and going left one can follow a curve of stars that describes the Scorpion's back and tail. Look further to the left, towards the moon, and one can see a "teapot" shape which is Sagittarius.
In the Southern Hemisphere, the Southern Cross and Centaurus will be high in the south by 8 p.m., with the four stars of the Cross below and west of Rigil Kentaurus, otherwise known as Alpha Centauri, at 65 degrees high. Looking at the zenith from the latitude of Melbourne, and slightly eastward, one can see Antares. Looking toward the southwest, below the Southern Cross, one can spot a circle of eight stars that is Vela, the Sail, and to the left of it is Carina, the Keel. Both of these are constellations that, with Puppis, the Poop Deck (which will have already mostly set), comprise the once-giant constellation Argo Navis, the legendary ship of Jason.
July full moon names
July's full moon is known as the Buck Moon because it coincides with the time of year when deer antlers are in full growth.
Native American peoples had many different moniker for July's full moon; the name "Thunder Moon" and others from the Old Farmer's Almanac reflect names from largely Algonquin-speaking peoples in what is now the northeastern United States and eastern Canada. But there were differences between nations. 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. Farther south, the Cherokee call the July lunation in their traditional calendar the Ripe Corn moon.
The Māori of New Zealand use a lunar calendar called the maramataka, which measures months between successive new moons. The July-to-August lunar month (which this year spans the new moons from June 21 to July 20) is called Here-turi-kōkā, or "The scorching effect of fire is seen on the knees of man," according to the Encyclopedia of New Zealand.
In China, the lunar calendar is in the sixth lunar month, or Héyuè (荷月), Lotus Month, when lotus flowers bloom.
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