The full moon of August arrives on tonight (Aug. 3), after the moon makes a close pass to Jupiter and Saturn in the night sky.
The moon will officially become full Aug. 3 at 11:59 a.m. EDT (1559 GMT), according to NASA's SkyCal. For New York City observers, the just-past-full moon will rise at 8:35 p.m., while the sun sets at 8:08 p.m. local time that day.
Full moons occur when the moon is exactly on the opposite side of the Earth from the sun. If the moon passes through the Earth's shadow, we see a lunar eclipse — but that doesn't happen every month because the moon's orbit is slightly inclined, so the moon usually misses the shadow. Full moons occur about every 29.5 days, which is just a little bit longer than the moon's orbital period. The reason is that the Earth is moving around the sun, so that by the time the moon gets to the same place it was in its last pass, the Earth isn't directly between the moon and sun anymore.
Related: 10 surprising lunar facts
On Aug. 1, the 12-day-old moon will appear close to Jupiter, passing within about three lunar diameters of the planet, or one and a half degrees, according to skywatching site In-the-sky.org. The two bodies will be in conjunction — sharing the same celestial longitude — at 7:32 p.m. EDT (2332 GMT). For skywatchers in New York City, that's about 24 minutes after the moon rises at 7:08 p.m. local time; the sun doesn't set until 8:10 p.m., so spotting Jupiter during the conjunction will be difficult as the sky will still be bright.
After sunset Jupiter is bright enough that it is one of the first "stars" visible at dusk. By about 8:30 p.m. in New York, both will be visible about 14 degrees above the eastern horizon, with the moon slightly below and to the right of Jupiter. The moon and Jupiter will make a triangle with the planet Saturn. Saturn will rise at about 7:27 p.m. and mark the left corner of the triangle.
By the next day (Aug. 2) the moon will pass by Saturn, though on the east coast of the United States the conjunction will happen during the day, at 9:08 a.m. EDT (1308 GMT). But once again the moon, Saturn and Jupiter will be grouped in the sky. By 8:30 p.m. in New York City Saturn will be about 11 degrees in altitude over the southeastern horizon, becoming visible as the sky darkens after sunset. The moon, meanwhile, will be to the left of Saturn and Jupiter will be to the left of the moon.
If you happen to live in Honolulu, the moment of conjunction will be in the predawn sky on Aug. 2, at 3:10 a.m. local time. The moon will pass about 2 degrees south of Saturn and be above the southwestern horizon. Both will be about 24 degrees in altitude.
On the night of the full moon, Mercury will be a "morning star" rising at 4:42 a.m. on Aug. 3 in New York, according to Heavens-Above.com calculations. The sun rises at 5:55 a.m., and by 5:30 a.m. the innermost planet will be about 8 degrees above the east-northeastern horizon in the constellation Gemini, making it a challenge to spot before the sky gets too bright.
Venus, meanwhile, will rise well before Mercury does, at 2:38 local time in New York, and will be in the constellation Taurus. Venus is bright enough that it is easy to find and at magnitude -4.3 will look like the brightest "star" in the vicinity. (Magnitude is a measure of brightness, with negative numbers indicating the brightest objects.) But unlike stars, planets don't twinkle — they tend to shine with a steady light. By 5:30 a.m. the planet will be a full 31 degrees above the horizon.
Mars, meanwhile, rises in New York at 11:07 p.m. local time on Aug. 3 and reaches its highest point at about 5:22 a.m. The planet is in the constellation Pisces, and as Pisces is made of relatively faint stars Mars will be obvious with its reddish hue and relative brightness.
Visible stars and constellations
Although the full moon tends to overwhelm the fainter stars, asterisms (or star patterns) such as the Summer Triangle — which consists of the stars Vega, Deneb and Altair — will be prominent and easily spotted. About an hour and a half after sunset in the Northern Hemisphere, you can look nearly straight up to find Vega, which, at mid-northern latitudes, is at an altitude of between 80 and 88 degrees (depending on how far north or south you are in the lower 48 states). Meanwhile, the constellation of Leo, the lion will be setting in the west.
By about 9:30 p.m. local time in mid-northern latitudes Scorpius, the scorpion is visible in the south, just underneath Ophiuchus, the snake bearer. Scorpius can be spotted by looking for Antares, a bright reddish star that marks the heart of the scorpion.
Ursa Major, the great bear, will be in the northwest after sunset. As you follow the "pointers" — the two stars in the front of the Big Dipper's bowl — to Polaris, the North Star, you can keep going and hit the W-shaped constellation Cassiopeia. Using the handle of the Big Dipper, one can "arc to Arcturus" by sweeping along the handle until you hit the eponymous star in Bootes, the herdsman.
How the Sturgeon Moon got its name
The full moon of August, according to the Old Farmer's Almanac, is sometimes known as the Sturgeon Moon. The name likely came from both colonists and Algonquian-speaking people in northeastern North America, as sturgeon are native to both Europe and the Americas.
But not every Native group in the region used the term. The Ojibwe, whose traditional territory is in what is now southeastern Canada, near the Great Lakes, referred to the eighth full moon of the year as the Blackberry Moon, which could also occur in July. The Cree of Ontario called the August full moon the Flying Up Moon because it was when young birds would fledge. In the Pacific Northwest, the Haida called it the Salmon Moon ("chíin kungáay"), according to Dolly Garza's book "Tlingit Moon & Tide."
In China, this year the August full moon will arrive in the sixth month, Héyuè, or Lotus month, for the blooming of said flowers.
Editor's note: If you snap an awesome photo of the moon or the lunar eclipse that you'd like to share with Space.com and our news partners for a potential story or gallery, send images and comments to managing editor Tariq Malik at email@example.com.
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