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    Spring is in the air — and in the night sky if you look closely

    March is the month when we emerge from the winter doldrums and welcome the arrival of spring. The days lengthen at their fastest pace and the bright stars of winter retreat. Importantly, for sky watchers, the astronomical beginning of spring occurs with the vernal equinox, which falls on March 19 at 11:06 p.m. Eastern time.

    At that moment, the center of the sun’s disk crosses the celestial equator into the sky’s northern hemisphere. This marked the traditional beginning of a new year in many cultures until Roman times, and today it sets the dates of important feasts and fasts in many religions.

    The point in the sky that defines the equinox is sometimes referred to as the “first point of Aries,” a term still widely used in astrology. The constellation of Aries, the Ram, was the location of the equinox back in Babylonian times, when the basic tenets of astrological practice were established.

    Today, the equinox actually lies some 30 degrees westward in the constellation of Pisces, the Fish, thanks to the 26,000-year cycle called “precession of the equinoxes.” In 3,000 years, the equinox will lie among the stars of Aquarius; it will return to Aries somewhere around the year 23,000.

    The term “equinox” implies the concept of “equal night,” when day and night are exactly 12 hours in duration. In reality, the upper limb of the sun pokes above the horizon a few days before the equinox. The actual date for 12 hours of daylight and darkness in D.C. this year is March 16, when Old Sol rises at 7:17 a.m. Eastern time and sets at 7:17 p.m.

    Moon notes, set that alarm

    You’ll find the waning moon gracing the morning sky as March begins. On the morning of the 3rd, early risers can catch the last quarter moon before dawn in the southern part of the sky. Less than a degree away is the bright red-tinted star Antares, the heart of Scorpius, the Scorpion.

    The new moon falls on the 10th. Luna waxes in the evening sky, reaching the full phase on the 25th. The traditional name for the March full moon is the Worm Moon, because the ground is soft enough for earthworms to find their way to the surface, providing a food source for birds and animals. Other traditional names are the Crow Moon and Sap Moon.

    If you want to be on time for any engagements on Sunday morning on the 10th, you will need to set your clocks ahead by one hour before going to bed Saturday night. Unless you live in Arizona or Hawaii, U.S. Code dictates that we all switch from standard to daylight time at 2 a.m. March 10. In my many years at the U.S. Naval Observatory, I have fielded hundreds of queries as to why this happens every year, but the rule is not ours to enforce.

    In the United States, civil time is governed by congressional authority through the Transportation Department. The observatory maintains a single reference time scale, UTC. We leave it up to others to figure out what to do with it.

    From the Big Dipper to Arcturus

    You can find the winter constellations that have helped us through the long winter nights in the western sky by mid-evening. By the end of the month, they’ll set by midnight. If you enjoy looking at Orion and its bright stellar companions, this is the last month to get a good view until late autumn.

    After March, a somewhat more subdued set of constellations will rise to take the night. The most recognizable pattern among them is the group of stars known to most of us as the Big Dipper.

    These seven stars form a distinctive pattern that outlines a respectable soup ladle, and it is usually one of the first asterisms that novice stargazers learn to recognize. It is also known as the Plough (plow) in Britain and Ireland, and the Wain (wagon) in other parts of Europe. The seven stars are part of the larger constellation of Ursa Major, the Great Bear. The two stars at the end of the Dipper’s “bowl” point northward to the star Polaris, which marks the north celestial pole.

    Follow the “pointers” to the south and you will encounter the constellation of Leo, the Lion, which consists of two distinct star groups. Leo’s brightest star, Regulus, sits below a semicircle of second-magnitude stars outlining the Lion’s head. To the east of Regulus, you’ll find a right triangle of stars that mark Leo’s hindquarters.

    Going back to the Big Dipper, if you follow the arc made by its “handle,” you will encounter the signature star of spring, Arcturus. It’s hard to miss as it is the brightest star in the northern sky and the fourth brightest overall thanks to its relatively nearby 37 light-year distance and its luminosity, which is about 170 times that of the sun. Its rosy tint reminds me of the colorful blooms that will follow as March passes to April.

    March may be something of a letdown for planet watchers. The only bright member of the solar system that’s easy to spot is Jupiter, which dominates the western sky during the evening hours. In early March, the giant planet sets between 11 p.m. and 10:30 p.m., but after we switch to daylight saving time, you should have no trouble spotting Jupiter shortly after sunset.

    Once Jupiter sets, though, the rest of the night lacks any bright planets to look for. Just before dawn, you may be able to spot Venus in the gathering twilight glow, but it will be very low in the southeastern sky.

    Toward the end of the month, though, we get a chance to see that most elusive of the planets, Mercury. The best time to look for Mercury will be 30 to 45 minutes after sunset on the evenings of March 17 through March 31, when it will be about 10 degrees above the western horizon. If you have them, use binoculars to look for it in the twilight glow. Once you’ve found it, you should be able to spot it with the naked eye.

    Celestial sightings in the D.C. area in March

    The weather is getting milder. Here are some places to look through a telescope this month.

    For a list of astronomy clubs, planetariums, science centers and observatories in the metro D.C., Baltimore and Richmond areas, see this website from the U.S. Naval Observatory.

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