Northern Sky: Sept 1 - 14, 2018

Deane Morrison is a science writer at the University of Minnesota.
She authors the Minnesota Starwatch column which can be found on the University of Minnesota website at astro.umn.edu.

She tells us what to look for in the night sky in our region.

NORTHERN SKY – by Deane Morrison                      September 1-14 2018
 
Now that September’s here, the skies are getting seriously dark. Venus is still in the west, but it’s sinking fast. It’s also coming toward us, on the way to zipping between Earth and the sun. If you have a small telescope, you can watch it go through phases. Venus appears as a fat crescent now, but the crescent gets longer and thinner as September goes by. 
 
Somewhat high in the west, we have the brilliant star Arcturus. At this time of year, I like to watch Arcturus slowly fall through the sky from night to night. Arcturus is the brightest star in Bootes, the herdsman, a kite-shaped constellation, and it’s right where the tail of the kite would attach to the sail. So as Arcturus and Bootes drop down toward the horizon, it always seems as if this heavy star is dragging the kite down with it.
 
Actually, Arcturus is falling on a grander scale. It doesn’t orbit horizontally around in the disk of the Milky Way like the sun. Instead, its orbit slices right through the galactic disk. But Arcturus isn’t plunging through the disk by itself; it has more than four dozen stellar companions. Together the group is called the Arcturus stream. One caution: Don’t confuse Arcturus with Jupiter, which is bright but rather low in the southwest after nightfall.
 
Mars and Saturn come out low in the south. Mars is east of Saturn; it’s also brighter and, of course, redder than Saturn. Between the two planets is the Teapot of Sagittarius. Above all this, we have the large Summer Triangle of bright stars. The lowest is Altair, in Aquila, the eagle. It’s pretty much right above Mars. Looking up and a little west of Altair, you’ll see the brightest star in the Triangle. That’s Vega, in Lyra, the lyre of Orpheus. Note the parallelogram of stars below Vega; they outline the lyre and they make a really beautiful sight through binoculars. East of Vega is the third star, Deneb, in Cygnus the swan. Deneb also marks the head of the Northern Cross, a notable feature of Cygnus.
 
The Summer Triangle is a rich area of sky to explore, with both the naked eye and binoculars. And a star chart, if it’s your first time. Look above Altair—again, that’s the lowest star in the Triangle—and try to make out a short and skinny constellation called Sagitta, the arrow. Then try immediately northwest of Sagitta’s feathers and see if you can find the dim but astonishingly realistic Coathanger hanging upside-down. You’ll need those binoculars to make it out. Finally, look to the east-northeast of Altair for Delphinus, the dolphin, which seems to be happily leaping into a dark sea.
 
The moon is new on September 9.  For a couple days before then, there’s a thin old crescent moon in the east before dawn. On Saturday, the 8th, the moon rises close to Regulus, the brightest star in Leo. Then comes Mercury, and the sun right behind it. Look about 40 minutes before sunrise, and good luck seeing all three of the other objects when the sun is so close.
 
And, starting on the 8th, try looking for the elusive zodiacal light in the east, just before the sky starts to get light. The zodiacal light appears as a broad but faint glow along the sun’s path and it comes from sunlight reflecting off the dust that extends far out into space in the plane of the solar system. If you don’t find the zodiacal light on the 8th, the following two weeks will also be good times to look, and the moon won’t interfere with your view of the morning sky.