By Deane Morrison

University of Minnesota

September opens with a new moon and a wandering Mars. The red planet is on the verge of leaving Scorpius en route to Sagittarius, the archer, and its well-named Teapot.

For much of the year we’ve watched Mars, Saturn, and Antares, the red heart of Scorpius, perform a ballet low in the south. Now Mars, having traveled eastward through Scorpius, leaves the scorpion and enters Ophiuchus, the snake handler, a large but little-known constellation. Mars sojourns through the southeastern section of Ophiuchus for the first three weeks of September before crossing into Sagittarius above the spout of the Teapot.

These days Mars really shows off its speed. As September goes by, watch Scorpius, along with Saturn (the bright light above Antares), wheel toward the southwestern horizon as Earth’s orbital motion leaves them behind. We’re also leaving Mars behind, but very slowly because the red planet’s own motion eastward allows it to hold its own as the stars stream by behind it. Mars will hang around in the evening sky well into next year—long after its companions in Scorpius have dropped out.

The Summer Triangle of bright stars rides high in the south after nightfall. Altair, the lowest, is the brightest star in Aquila, the eagle. Above and slightly west of Altair, brilliant Vega and a parallelogram of stars form Lyra, the lyre of Orpheus. East of Vega, Deneb twinkles in Cygnus, the swan, and its most famous feature: the Northern Cross. Look for the pointed form of Sagitta, the arrow, sailing above Altair, and also little Delphinus, the leaping dolphin, northeast of the star.

September’s full harvest moon shines the night of the 16th. Not quite six days later, at 9:21 a.m. on the 22nd, the autumnal equinox ushers in fall. At that moment the sun crosses the equator into the southern sky and lights Earth from pole to pole. It’s not until the 25th that we see a day and night of equal length, however. A major reason is because Earth’s atmosphere is a gigantic lens that bends sunlight over the horizon and makes the sun visible for a few minutes before and after the actual moments of rising and setting, respectively.

Mercury pops into the morning sky just before the equinox.