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Starwatch: March ushers in spring equinox

With two full moons and the spring equinox, what's not to love about March?

The first full moon arrived at 6:51 p.m. March 1, barely an hour after moonrise and just a couple of days after perigee, its closest approach to Earth in a lunar cycle. This means it rises about as round and luminous as any full moon gets.

The second arrives at 7:37 a.m. March 31. As the second full moon in a calendar month, it qualifies as a blue moon. However, it sets that morning shortly before the instant of fullness, so you may want to check your local time of moonset before deciding whether to get up to see it or to enjoy it the evening of March 30.

Venus and Mercury appear very low in the west after sunset, bathed in the sun's afterglow. The planets are closest March 3, but easy to tell apart because Venus outshines Mercury. After March 15, Mercury plummets toward the horizon and is soon lost.

In the predawn sky, look south to see brilliant Jupiter. East of Jupiter, Mars is brightening as it moves swiftly eastward. Its motion carries it away from Jupiter and Scorpius, with its red heart, Antares (the "rival of Mars"), and toward Saturn, a shiny dot above the Teapot of Sagittarius. Mars waxes brighter every morning because Earth is gaining on it in the orbital race. This summer, we'll lap the red planet and it will be a treat for the eye.

On evenings between March 3 and 18, look for the elusive zodiacal light, a faint glow extending up from the western horizon along the sun's path shortly after nightfall. It comes from sunlight reflecting off dust in the plane of the solar system.

Spring arrives with the vernal equinox at 11:15 a.m. March 20. At that moment, the sun crosses the equator into the northern sky and Earth will be lighted from pole to pole.

With the sun's crossing comes a turning point in day length. During fall and winter, travelers in the Northern Hemisphere who are heading north see the day length shorten. But after the March equinox, going farther north means a longer day length. Also, the day length increases fastest around the time of the spring equinox because this is when the sun is moving most rapidly north.

Visit the Marshall W. Alworth Planetarium in Duluth at d.umn.edu/planet.

Find U of M astronomers and links to the world of astronomy at astro.umn.edu.

Minnesota Starwatch is a newsletter describing the night sky in the Midwest. Updated monthly, it is produced by Deane Morrison, University of Minnesota Institute for Astrophysics. Find U of M astronomers and links to the world of astronomy at astro.umn.edu.

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