Minnesota Star Watch: A grand opening to February

Published 6:21 am Saturday, January 26, 2019

A University of Minnesota Feature by Deane Morrison

February opens with Venus and Jupiter lighting up the southeastern predawn sky. As the month goes by, Venus drops toward the rising sun while Jupiter, now higher than Venus, rapidly pulls away westward. Saturn, following Jupiter, passes Venus between the 17th and 19th. On the 28th, Jupiter, a waning moon, Saturn and Venus form, in that order, a descending line to the horizon.

High above and west of the planets shines brilliant Arcturus, the jewel of Bootes, the herdsman. Look to the left of Arcturus for its rival Vega, the brightest of the Summer Triangle of stars.

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In the evening sky, Mars, in the southwest, drifts slowly westward as the bright winter constellations close in on it. These constellations are now high in the south during the mid-evening hours—in prime viewing position. Lowest in the bunch is Canis Major, ornamented by Sirius, the night sky’s brightest star. Only 8.6 light-years away, Sirius owes most of its brilliance to its proximity.

Sirius is actually a star system; it includes a white dwarf star that has the same mass as the sun, but is the size of Earth, according to Robert Gehrz, professor of astrophysics at the University of Minnesota. “A piece of it the size of the last segment of your little finger would weigh two tons,” he notes.

Someday, billions of years from now, our sun will become a white dwarf, too, as it burns the last of its nuclear fuel and casts off its outer layers, leaving only its hot core and a halo of gas and dust called a planetary nebula.

To the upper left of Sirius is another star with a white dwarf companion: Procyon, in Canis Minor. Procyon means “before the dog,” a reference to its habit of rising just before Sirius, the Dog Star. To the right of Procyon is Orion, with reddish Betelgeuse at his northeast shoulder. Together, Betelgeuse, Procyon and Sirius form the Winter Triangle of bright stars.

February’s full moon arrives on the morning of the 19th, just seven hours after making its closest approach to Earth in this lunar cycle. Therefore, it qualifies as another large, luminous supermoon. However, it sets early that morning, before the moment of perfect fullness. To see it at its best, check your local time of moonset and look to the west about an hour in advance.

February may be one of the coldest months, but at least it gives us the distraction of Groundhog Day, an astronomically based holiday. The ancient Celts called it Imbolc, or lamb’s milk, one of four “cross-quarter days” falling midway between a solstice and an equinox. It was also considered the first day of spring. Our Groundhog Day comes from Celtic and other traditions that held that a clear day with shadows portended continued cold and winter, but clouds meant an early spring.

Find U of M astronomers and links to the world of astronomy athttp://www.astro.umn.edu.