March 2006

by Deane Morrison

The young moon that heralds the arrival of March waxes to a mature full moon on the 14th. That evening, the moon will rise swathed in Earth's penumbra, or light outer shadow. In other words, the moon undergoes an eclipse, and it starts without us. This one is unusual in that the whole moon passes through the penumbra without any part of it touching the umbra, or dark inner shadow. The height of the eclipse occurs at 6:47 p.m. CST, about 26 minutes before moonrise in the Twin Cities. When it does rise, the moon will be subtly shaded, with only its bottom region noticeably darkened. The eclipse ends at 8:13 p.m., when the moon relinquishes its last point of contact with Earth's shadow.

The full moon of March has been called the worm moon by some Algonquin Indian tribes, for the softening of the ground and the reappearance of earthworm casts at this time of year. Other tribes called it the crow moon, after the cawing that presages the end of winter; the crust moon, for the crust on snow that has melted and refrozen; or the sap moon, to celebrate the start of maple sugaring season.

Recently, the moon was in a news story that connected folklore to science. Researchers have found evidence that the "man in the moon" was created when the young, largely molten moon was hit by a large object--perhaps an asteroid--on its far side. The impact appears to have sent a shock wave clear through the moon, and may have resulted in fissures on the side facing Earth. Such fissures could have allowed molten rock from the moon's mantle to ooze to the surface and pool, forming the roundish dark "seas" that give the man in the moon the appearance of eyes. To this day, the moon carries the scars of such a collision: a large depression on the far side and a bulge on the near side.

The spring, or vernal, equinox occurs at 12:26 p.m. on the 20th. At that moment the sun will cross the equator into the northern sky. The sun moves fastest around the time of the equinoxes, and the relatively rapid warming associated with its northern movement stirs up the fabled March winds.

March is the last good month for viewing the bright winter constellations. This year, they enjoy extra beauty thanks to two planets. Mars, fading but still bright, glides through Taurus, just above Orion, and Saturn hugs the Beehive star cluster in Cancer, just southeast of the Gemini twins. Late in the evening, Jupiter rises to enhance the view. The king of planets comes up more than five hours after sunset on the 1st, but the interval shortens to about three hours before the month is out. Once Jupiter is up, viewers can see the three bright outer planets--Jupiter, Saturn and Mars--strung from east to west among the stars.

Venus dominates the predawn sky. The brilliant orb appears after the summer constellations Scorpius and Sagittarius, which rise by about 4 a.m.

As the month progresses, Leo, the lion, leads the march of spring constellations. Look above the lion, below the bowl of the Big Dipper, and see if you can find the stars called the Three Leaps of the Gazelle. They are three pairs of stars in a line extending northwestward from a spot just above the lion's hindquarters. Gazelles are known for their incredible, graceful leaps; perhaps this one is fleeing from Leo.