This is Dudley Observatory’s Skywatch Line for Friday, October 22, through Sunday, October 24, written by Sam Salem.
On Friday, Sun rises at 7:17am and sets at 6:01pm; Moon sets at 9:10am and rises at 7:11pm.
There are three bright stars you might notice flashing or twinkling fiercely in the October night. They are Capella in Auriga, Arcturus in Boötes, and Sirius in Canis Major. Capella shines at magnitude 0.24, making it the 6th-brightest star in Earth’s sky, not including our Sun. And it’s low in the sky, in the northeast direction, at nightfall or early evening as seen from mid-northern locations, at this time of year. Capella is the brightest star in the constellation Auriga the Charioteer. But since antiquity it’s carried the name Goat Star. You might pick it out just by gazing northeastward from a Northern Hemisphere latitude during the evening hours in October. To be sure you’ve found Capella, look for a little triangle of stars nearby, an asterism called The Kids. Capella flashes red, blue, and green when it’s close to the horizon and seen through a thick layer of Earth’s atmosphere.
Arcturus is in the constellation Boötes the Herdsman. It’s an orange-colored star, in the northwest in the evening in October. You can always know you’ve found Arcturus if you also notice the Big Dipper, also in the northwest in early evening, nearby. The arc of the Big Dipper’s handle can be extended outward to Arcturus. Arcturus is about the same brightness as Capella, but it’s not as noticeable because on October evenings Capella is ascending in the sky and Arcturus is descending. Therefore, Capella shines most of the night, while Arcturus not long after the Sun.
Sirius in the constellation Canis Major the Greater Dog is the brightest star in the night sky. This star is famous for twinkling in different colors. Sirius is now in the south before dawn, as seen from the Northern Hemisphere.
Auriga the Charioteer is a popular constellation in autumn, because its flashing star, Capella, advertises its presence. Auriga houses three-star clusters, easy targets to hunt down with binoculars. Auriga is a north circumpolar constellation, meaning that it is close enough to the North Star that people in the Northern Hemisphere can see the constellation on any night of the year. But some times of the year are definitely better than others. If you want to see the entirety of Auriga, start looking for the constellation and flickering Capella in the autumn.
This weekend, the bright star Deneb, in constellation Cygnus, the Swan, climbs to its highest point in the sky around 7:30 p.m. This member of the famous Summer Triangle asterism is shifting ever westward in our sky each day, as Earth travels around the Sun. Its transit at nightfall in October is a hallmark of the year. It marks a shift toward winter in the Northern Hemisphere.