Minnesota Starwatch: September 2017

September opens with Venus hosting winter constellations in the eastern predawn sky. West of the planet, the bright star Procyon, in Canis Minor, the little dog, rises at almost the same time as Venus. About 40 minutes later, Sirius, the brightest of stars, rises even farther west in Canis Major, the big dog.

As the month goes on, the winter stars sweep westward; Venus drops toward the sun, rising later every morning; and the spring constellation Leo, the lion, becomes the planet’s new starry companion. In mid-September, Mars and Mercury enter the morning sky above the eastern horizon. Mars is dim and climbs slowly, but brighter Mercury, as usual, quickly pops (up) and drops. On the 16th, Mercury passes near Mars in the sun’s foreglow.

On the 18th, look an hour before dawn to see, stacked from top to bottom: Venus; Regulus, the brightest star in Leo; an old crescent moon; Mars; and Mercury. Mars and Venus are rapidly approaching each other en route to a very close pairing in early October.

In the evening sky, Jupiter all but disappears into the sun’s afterglow this month. This leaves Saturn, in the south to southwest, the lone evening planet visible to the naked eye. High in the southwest, the Summer Triangle of bright stars encloses a patch of sky replete with constellations big and small, plenty to delight anyone with a star chart.

Autumn’s “water” constellations are now moving into prime evening positions in the south. Capricornus, the sea goat, is westernmost. Moving eastward, we see spidery Aquarius, the water bearer; then the Circlet of Pisces. Above the Circlet is the Great Square of Pegasus. Below Aquarius, the bright star Fomalhaut marks the mouth of Piscis Austrinus, the southern fish.

September’s full moon arrives at 2:03 a.m. on the 6th. And at 3:02 p.m. on the 22nd, the autumnal equinox ushers in fall.

The University of Minnesota offers public viewings of the night sky at its Duluth campus. For more information and viewing schedules, see the Marshall W. Alworth Planetarium at: d.umn.edu/planet.—Deane Morrison