Minnesota Starwatch: July
From Deane Morrison
As night falls, the trio of Mars, Saturn and the red star Antares comes out in the south and southwest. If you haven’t seen this sight, now’s the time to catch it.
Mars is in the southwest, traveling eastward against the background of stars. On the 13th it glides 1.3 degrees north of Spica, the brightest star in Virgo. Next in its sights is Saturn, a beacon in the south beside the sinuous form of Scorpius.
Mars’ motion brings it closer to Antares, the heart of the scorpion. Antares means “rival of Mars,” but there’s really no comparison. Antares is one of the largest stars known, with a diameter about 850 times that of our sun. But for all its intrigue, Mars is small; its diameter is 53 percent of Earth’s and its volume only 15 percent. Its low surface gravity means that you would weigh only 38 percent as much if you moved to the Red Planet.
Antares glows above the southern horizon, ornamenting a constellation that looks like its namesake. The scorpion’s claws extend westward toward Saturn, while its tail dips below the horizon (from our northern point of view) then curves up into view below and east of Antares. Above the tail, the spout of the teapot of Sagittarius is poised to pour out its contents, and the tiny teaspoon of stars hangs over the handle of the teapot.
Above Mars and Saturn, brilliant Arcturus burns at the base of kite-shaped Bootes, the herdsman. Moving east again, we encounter Corona Borealis, the Northern Crown, a hanging semicircle of stars; then the hourglass form of Hercules, kneeling upside down when we observe him while facing south; and finally the Summer Triangle of bright stars.
Below Hercules, try to find the form of Ophiuchus, the snake handler. You’ll need a star chart, but if skies are dark the rewards are great: Serpens Caput, the snake’s head, below Corona Borealis; Serpens Cauda, the snake’s tail, above the teapot; and the handler plus the rest of the snake in between.
The moon makes a round of visits, starting on the 5th, when a first-quarter moon separates Mars and Spica. A waxing gibbous moon visits Saturn on the 7th, and the morning of the 22nd, a waning crescent hangs with the Hyadesstar cluster and the bright star Aldebaran in Taurus. The moon ends its rounds by passing Venus in the eastern predawn sky on the 24th.
The full moon arrives at 6:25 a.m. on the 12th. This will be shortly after moonset, so you may want to enjoy it the night before. July’s full moon has been called the full thunder moon, and also the buck moon, because male deer are now growing velvet-coated antlers.
Earth reaches aphelion, the farthest point from the sun in its orbit, on July 3. At that moment we’ll be 94.5 million miles from our parent star. That’s about 3.5 percent farther than at our closest approach, which occurs in January.
The University of Minnesota offers public viewings of the night sky at its Duluth and Twin Cities campuses. For more information and viewing schedules, see:
Duluth, Marshall W. Alworth Planetarium: www.d.umn.edu/planet
Twin Cities, Minnesota Institute for Astrophysics (during fall and spring semesters): www.astro.umn.edu/outreach/pubnight