The new moon occurs on Friday (Oct. 16), at 3:31 p.m. EDT (1931 GMT), on the same day that our natural satellite reaches perigee, or the closest point to Earth in its orbit, according to NASA's SkyCal site.
New moons happen when the moon is directly between the sun and Earth. About every 29.5 days the two bodies share the same celestial longitude, an alignment also called a conjunction. Celestial longitude is a projection of the Earth's own longitude lines on the celestial sphere. If one draws a line from Polaris, the North Star due south toward the sun, that line also hits the new moon.
On Oct. 16 the moon also reaches the closest point in its orbit to Earth. The average distance between Earth and the moon is 238,855 miles (382,500 kilometers), according to NASA, but it varies somewhat because the orbit is not perfectly circular. About four hours after the new moon, at 7:46 p.m. EDT (2346 GMT), the moon will be 221,775 miles (356,912 km) away. Were the moon full it would be a "supermoon" — appearing about 10% larger than normal, but new moons are invisible to ground-based observers unless the moon passes between the sun and Earth and there is a solar eclipse.
Related: Zany moon monikers: October's 'Blue Moon' and other lunar terms explained
A line of planets
The summer stars are setting at this time of year, and just after sunset at around 8 p.m. local time on Oct. 16 you can see Jupiter and Saturn in the southwest, with Jupiter the brighter planet to the right (from the Northern Hemisphere). Jupiter and Saturn will be in the constellation of Sagittarius, the archer, and will be about 23 degrees and 26 degrees above the horizon, respectively, as seen from New York City.
Continuing eastwards (left), Mars will be in the constellation Pisces, the fishes. Pisces is made up of relatively faint stars, so from a city location Mars will be obvious by its reddish hue. On the night of the new moon in New York City Jupiter, Saturn and Mars respectively set at 11:10 p.m., 11:42 p.m. and 6:05 a.m. on Oct. 17, according to Heavens-Above.com calculations.
Venus, meanwhile, rises as a morning star, and is one of the brightest objects in the sky. In New York on Oct. 16 the planet rises at 4 a.m., while the sun doesn't rise until 7:08 a.m. local time. By 6:45 a.m. the planet will be 30 degrees in altitude, in the constellation Leo, the lion. A fun exercise is to see how close to sunrise one can still spot it — Venus will be shining at magnitude -3.9, which makes it about nine times as bright as the brightest star we can see, Sirius, the "Dog Star" in Canis Major. (Magnitude is a measure of brightness, with negative numbers denoting the brightest objects.)
Mercury will be nearly impossible to see, as it rises after the sun and sets almost immediately after sunset. In New York City the planet sets at 6:37 p.m. local time on Oct. 16, and the sun sets at 6:13 p.m., so Mercury will be no more than a degree above the horizon by the time the sky gets dark enough to see it at all.
For Southern Hemisphere skywatchers the situation will differ — as will the altitudes of planets. In Melbourne, Australia, the new moon occurs at 5:31 a.m. local time on Oct. 17. Looking at the sky about a half hour after sunset on that day, which occurs at 7:39 p.m., Mercury will be low in the west, just about 10 degrees above the horizon, so keen-eyed observers might be able to catch it against the sky as it gets dark out.
The reason is that the plane of the ecliptic — the line that describes the Earth's orbit projected against the sky — is at a steeper angle to the horizon. The moon, Venus and other planets all travel close to that line in their passage across the sky against the background stars. The arrangement puts Mercury higher after sunset than in mid-northern latitudes.
The line of Jupiter, Saturn and Mars, meanwhile, is "flipped." At about 8 p.m. local time in Melbourne, Mars will be low in the sky just north of east, about 10 degrees above the horizon, and moving one's eyes left — to the north — one encounters Saturn and then Jupiter. The big difference between the view from Down Under and the mid-northern latitudes of the U.S. and Europe is that Jupiter and Saturn are much higher in the sky — at 8 p.m. they are, respectively, 69 and 71 degrees above the horizon.
Stars and constellations
In mid-October, the "summer" constellations of the zodiac — Sagittarius, Ophiuchus and Scorpius — are in the western half of the sky by evening. Just after sunset, at around 8 p.m. local time, the "wet region" of the sky is prominent to the south. The wet region is called that because so many of the constellations are water-themed; at 8 p.m. looking south one sees Capricornus, Aquarius, and Pisces (as one moves the point of view to the east). Just below Pisces is Cetus, the whale. All of these constellations are relatively faint; none has a first-magnitude star and from urban locations they can be difficult to see.
Closer to the southern horizon one can see Fomalhaut, the brightest star in Piscis Austrinus, the southern fish. Fomalhaut is a first-magnitude star that is also one of the sun's closest neighbors, "only" 25 light-years away.
To the north from Aquarius you can see the constellations of Pegasus and Andromeda, marked by an asterism called the Great Square. One corner of the square is Andromeda's head, while the other three mark the wing of Pegasus, the legendary flying horse ridden by Perseus to save Andromeda from a sea monster.
From Andromeda's head one can trace two lines of stars and find the Andromeda Galaxy, which can be spotted from a dark-sky site with the naked eye.
Meanwhile, the Southern Hemisphere observers will see the Southern Cross constellation near the meridian just after sunset, just west of south, and just above and to the right will be the Centaurus constellation, home to Alpha Centauri, the closest star to Earth. Alpha Centauri is quite bright and in a sort of cluster of bright stars in that region of the sky — one can find it using the Southern Cross and tracing a line across the "spar" of the cross to the north.
Looking just east of south after sunset, one can see the Large Magellanic Cloud, a smaller galaxy that orbits our own Milky Way; the nearest bright stars include Achernar, the end of the constellation Eridanus, the river, which begins near the feet of Orion, the hunter (which is still below the horizon from Australia).
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