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The Sky This Week, 2016 February 16 - 23

Swimming in a lunar "sea".
MOON_120924-21h51m_02small.jpg
Gibbous Moon, 2012 SEP 24, 01:51 UT
Imaged with an 80 mm (3.1-inch) f/6 refractor and Canon EOS Rebel T2i DSLR
Mare Imbrium is bisected by the terminator at the upper left.

The Moon waxes through her gibbous phases this week, with Full Moon occurring on the 22nd at 1:20 pm Eastern Standard Time. February’s Full Moon is popularly known as the Snow Moon or Hunger Moon, indicative of the harsh weather that often accommodates the year’s shortest month. Look for the Moon near the bright star Regulus on the evenings of the 21st and 22nd. On the 23rd she cozies up to bright Jupiter, with less than two degrees of space between them.

Luna’s gibbous phases reveal some of her most interesting terrain, and I often like to spend evenings at the telescope checking over the changes revealed on successive nights. The largest of the Moon’s so-called "seas" gradually become visible as the terminator line slowly increases the Moon’s phase. The highlight for the next few nights is the Mare Imbrium, the "Sea of Rains", which forms the largest circular basin on the Moon’s surface. The Imbrium basin is the result of an impact by a very large asteroid some 3.9 billion years ago that gradually filled with lava erupted from the Moon’s interior. The distance across its prominent rim is some 1250 kilometers (800 miles) and is peppered with many solitary craters of varying sizes. Look for a number of isolated mountain peaks near the northern rim of mare Imbrium. Prominent also are the large dark-floored crater Plato and the large indentation in the Mare’s northeast rim. This feature, known as the Sinus Iridum or "Bay of Rainbows", is not far from the site of the most recent soft-lander probe to the Moon, the Chinese Chang’e 3, which touched down and released a small rover on December 14, 2013.

The Moon washes out the darker sky this week, leaving the bright and colorful stars of the Great Winter Circle to capture your gaze. In some ways the bright sky helps one to identify the basic constellation patterns without the "chaff" of many fainter stars to add to an already confusing sight. The basic stars of Orion, for instance, show up very well against the brighter sky background. It’s relatively easy to find the Hunter’s "shoulders" and "knees" split by the diagonal trio of the "belt" stars. Other outlines become simpler to recognize as well. The constellation of Auriga, the Charioteer, lies directly overhead in the evening and forms a very nice pentagon shape. The southernmost star in the pentagon, Al Nath, is "shared" as the northern "horn" of Taurus, the Bull, whose face is delineated by the Hyades star cluster and the bright reddish star Aldebaran. Opposite Aldebaran, along the line that passes through Orion’s belt stars, is dazzling Sirius, the brightest star in the sky.

Bright Jupiter is preparing to make his grand entrance to the evening sky. The giant planet now rises just over an hour after sunset, and by the end of the week he rises very close to the nearly full Moon. Old Jove is now just a few weeks from opposition, when he appears in the sky all night long. This is the best time of the current apparition to observe Jupiter and his four bright Galilean moons as the planet’s apparent diameter grows to its largest size in the weeks surrounding opposition. If you have a telescope of four inches aperture or more look for the planet’s famous Great Red Spot on the late evenings of the 17th and 19th. On the 20th you can watch the shadow of Io drift across the planet’s vast, streaked face.

Mars stays close to the meridian as morning twilight begins to brighten the eastern sky. The red planet is drifting eastward toward the stars that form the "head" of Scorpius, the Scorpion, about 15 degrees west of the bright star Antares. This star’s name means "Rival of Mars", so it’s a good time to compare the two and admire their ruddy tints.

You can compare the colors of Mars and Antares to the golden hue of Saturn, which lies just over eight degrees northeast of Antares. You’ll find the ringed planet in the southeastern sky as dawn begins to brighten the horizon. Point a small telescope at him and you’ll be rewarded with a wonderful view.

Venus can still be found low in the southeast before the Sun rises, but you’ll only be able to see her in the brightness of morning twilight. You’ll need a clear flat horizon to catch a good glimpse of her before the arrival of the Sun.

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