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The Sky This Week, 2014 March 18 - 25

Spring is definitely coming. At least as far as the stars are concerned!

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 The USNO's 12-inch (30.5-cm) f/15 Alvan Clark/George Saegmüller refractor telescope

Originally completed in 1895, it was re-located to another dome in 1957, then dismantled in 1970.
Restored to its original dome in 1980, it has been used as a visual observing instrument since then.


The Moon wanes in the late evening and early morning sky this week. Last Quarter occurs on the 23rd at 9:46 pm Eastern Daylight Time. Luna begins the week forming an attractive triangle with the bright ruddy planet Mars and the blue-tinted star Spica, arcing across the sky together during the wee hours of the 19th. Luna then encounters Saturn on the morning of the 21st before finishing the week among the rising stars of one of summer’s signature constellations, Scorpius the Scorpion. Early risers will find Luna scudding over the southern horizon late in the week if they rise before dawn.

Despite the harsh weather that March has thrown at us here in the Washington, DC area this year, spring is definitely on the way! The Vernal Equinox will occur on the 20th at 12:57 pm EDT despite any appearances to the contrary. At that instant the center of the Sun’s disc crosses the celestial equator above a spot located over the southern reaches of Colombia in South America. If the sun were a pinpoint of light and the Earth was a perfect sphere with no atmosphere all parts of the planet would experience exactly 12 hours of daylight and night; but the Sun subtends a disc of about 30 arminutes’ diameter, the Earth is kind of lumpy, and we have an atmosphere. All of these factors combine to produce days and nights of "equal night" that fall a few days before the equinox, depending on location. Here in Washington our "equal night" fell on St. Patrick’s Day, so despite the snow storm daylight will exceed night from now until a few days after the autumnal equinox. We know that warmer weather will soon follow!

March 21st begins the third campaign in this year’s "citizen science" participation program called "Globe At Night". This will be the last month to estimate the brightness of your local sky by using the familiar constellation pattern of Orion the Hunter. The premise is quite simple: wait until it’s fully dark (around 9:00 pm), locate Orion in the southwestern sky, and report the number of stars that you see compared to finder charts located on the program’s website. If you have a smart phone there are even apps that will let you measure the sky brightness using the built-in camera! Either way, if you take the time to make an observation you’re contributing to our understanding of the effects of light pollution on a global scale.

Bright Jupiter now appears near the meridian almost as soon as the Sun sets. He’s very easy to find in evening twilight, and he still dominates the evening sky. This week he passes just five arcminutes south of a 6th-magnitude star as he slowly drifts eastward among the stars of Gemini. They will be closest on the evening of the 20th. As always, Jupiter’s four bright moons will appear in various configurations around the planet, and on the 20th the moon Europa’s shadow will move across the planet’s disc starting at around 10:00 pm EDT.

The Moon rises with ever-brightening Mars just after 9:30 pm on the 18th. While Luna abandons the red planet on subsequent nights, Mars rises five minutes earlier, so by the end of the week you’ll see him low in the southeast by 9:00. By 1:00 am he’s high enough to command your attention, and owners of modest telescopes can get a good peek at his surface details. Unlike most planets in the solar system, when you look at Mars you’re looking at a solid surface, not the tops of dense cloud-filled atmospheres.

Saturn follows Mars by about two hours, so he is best seen just before dawn. It should be worth the effort to snag him in the telescope, though, since he presents a wonderful view ensconced among his distinctive rings.

Venus is probably now quite familiar to commuters headed east toward Washington in the pre-dawn hours. The dazzling planet reaches her greatest western elongation from the Sun on the 22nd, but her far southerly declination keeps her close to the southeast horizon.

USNO Master Clock Time
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