Geminid meteor shower, 2012 © Mike Lewinski
The sixth full Moon of the year was known to indigenous Americans by various names including the Buck Moon and Thunder Moon (Algonquin), the Mid-Summer Moon (Ojibway), and the Moon of the Horse (Apache). Being opposite the Sun, which passes high across the sky during the summer, the corresponding full Moon arcs very low across the sky.
As it rises, this night's full Moon passes through the outer fringe of Earth's shadow, causing a barely perceptible penumbral lunar eclipse. Details can be found in Highlights.
The Moon has completed the third quarter of its orbit around Earth and begins the last quarter before reaching its next new phase (that's why those two terms are interchangeable). Located against the stars of Pisces the Fishes, it rises around midnight between the 12th and 13th. Its Earthward face appears exactly half-lit, with the terminator (the edge of its sunlit side) running straight down its center.
Jupiter reaches opposition and rises at sunset. It's visible all night against the stars of Sagittarius the Archer. More details are in the Jupiter section of this quarter's Planet Watch.
New Moon is the start of a new lunar phase cycle, or lunation. Sighting of the youngest, thin crescent after new marks the start of Dhul-Hijjah, the twelfth month of the Moon-based Islamic calendar. Since the new Moon is at 10:33 am PDT, sighting of the first crescent is not possible until perhaps just after sunset the following day (July 21), although it will be challenging, with the super-thin crescent very low in the glow of twilight (binoculars may be needed).
Saturn reaches opposition just a week after Jupiter. Located against the stars of Sagittarius the Archer, it rises at sunset and is above the horizon all night, very close to Jupiter. See Saturn's entry in Planet Watch for more information.
The first quarter Moon rises at midday and is located high in the south at sunset. At this time, it is only 1/11 as bright as a full Moon, but is still bright enough to obscure faint nebulae, galaxies, and star clusters from view, which is why many skywatchers limit their observations to times when the Moon is at less than a quarter phase and the light of the crescent Moon isn't as intrusive.
Indigenous Americans gave the full Moon of August names such as the Sturgeon Moon (Algonquin), Plum Moon (Shawnee), and the Moon When Young Ducks Begin to Fly (Cree). It rises at sunset, with the stars of the constellation Capricornus the Sea-Goat appearing around it as night falls.
The Moon is at last quarter at 9:45 am PDT, when it's high in the west, setting close to 2 pm.
Peak date for this year's Perseid meteor shower, which occurs with a waning crescent Moon. Details and observing tips in Highlights.
New Moon at 7:41 pm PDT. Sighting of the first visible crescent after sunset on the 19th may require binoculars, since the thin Moon is very low and difficult to spot in the sun's lingering glow. This sighting would mark the start of the month Muharram in the Moon-based Islamic calendar.
Moon at first quarter, located in the south at sunset. After dark, look for the stars of Scorpius the Scorpion around it, particularly the reddish star Antares, which represents the Scorpion's heart.
This month's full Moon was known to Native Americans as the Corn Moon or the Barley Moon, among other names. Sometimes, it's called the Harvest Moon—but not this time. That name is reserved for the full Moon closest to or (by another rule) the first one following the September equinox. That doesn't happen until October 1.
The Moon is at last quarter around 2:30 am PDT. Located against the stars of Taurus the Bull, it rises about the previous midnight and is nearly overhead at dawn, setting around mid-afternoon.
New Moon is at 4 am PDT. Sunset for San Francisco is a little more than 15 hours later, at 7:13 pm—still just a bit too soon for the young crescent to be visible. This observation, which will be easier just after sunset on the 18th, marks the start of the month Safar in the Islamic calendar.
The September equinox occurs at 6:31 am PDT, marking the start of Autumn in the Northern Hemisphere and of Spring in the Southern Hemisphere.
The first quarter Moon is located due south at sunset, setting just before midnight. After dark, look nearby for Jupiter and Saturn.
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