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Planets shine in May

Deane Morrison

Last month Earth caught up to Mars in the orbital race. In May, it’s Saturn’s turn to be overtaken.

We lap the ringed planet on the 10th, when the sun, Earth and Saturn line up and Saturn is at opposition, or opposite the sun from our point of view. Like a full moon, the planet will rise in the southeast at sunset and be up all night, shining from the rather dim constellation Libra.

In mid-evening, after skies darken, we’ll be treated to the sight of all three of the outer planets visible to the naked eye, and all will be bright. Jupiter, the brightest, will be up in the west-northwest; Mars in the south, just northwest of the bright star Spica, in Virgo; and Saturn in the east. If you have any trouble spotting Saturn, it’ll be the bright object above the rising moon on the 14th.

Besides its lovely rings, which are now tilted at a favorable angle of 22 degrees from horizontal, Saturn has the distinction of having a very low density. The planet is lighter than water and would float in an ocean, even a freshwater one, if any were big enough. Saturn’s orbit keeps it between about 9 and 10 times as far from the sun as Earth’s average distance, and it takes 29.5 years to complete an orbit.

Speaking of rings, astronomers have just discovered the first asteroid — and the smallest known object — with rings. It’s a rock called Chariklo, just 155 miles in diameter, orbiting between Saturn and Uranus. Its double ring is thought to come from the debris of a collision.

Above Spica, see if you can make out the kite-shaped form of Bootes, the herdsman. The kite extends northeastward from the brilliant star Arcturus, the brightest star in the northern dome of sky. Arcturus is also a bit of a maverick: Instead of orbiting around the disk of the Milky Way like our sun and most other stars, it is slicing down through the disk, and at great speed.

In the morning sky, Venus rises almost two hours ahead of the sun. Our sister planet is receding as it heads toward the far side of the sun, but it will be with us for a few more months.

May’s full moon, known to many Algonquin Indians as the full flower moon, arrives at 2:16 p.m. on the 14th. We’ll have to wait till around sunset to see it, but as it rises against a pale sky, what’s not to love?

The University of Minnesota offers public viewings of the night sky at its Morris, Duluth, and Twin Cities campuses. For more information and viewing schedules in Duluth, visit the Marshall W. Alworth Planetarium at