Yes, the dazzling conjunction of the brilliant planets Venus and Saturn at dusk/nightfall counts as this month’s marquee event, but let’s not forget about the less showy conjunction of two modestly-bright celestial lights – the red planet Mars and the star Zubenelgenubi – in the morning sky. Get up 1 1/2 hours (or more) before sunrise to view the close-knit morning couple lighting up the predawn darkness all this upcoming week. The conjunction happens on or near December 12, 2019.
For your convenience, we give you the approximate rising time of Mars for various latitudes (given an absolutely level and unobstructed horizon) for the next several days:
40 degrees north latitude
Mars rises 2 3/4 hours before the sun
Equator (0 degrees latitude)
Mars rises 2 1/3 hours before the sun
35 degrees south latitude
Mars rises 2 hours before the sun
Want more specific information? Click here for a recommended sky almanac.
Mars and Zubenelgenubi, the constellation Libra‘s alpha star, shine plenty close together on the sky’s dome all this upcoming week. In fact, the twosome will easily fit inside a single binocular field all the while. You can distinguish ruddy Mars from Zubenelgenubi, because Mars is the brighter of the two – better than twice as bright as Zubenelgenubi. However, both Mars and Zubenelgenubi are rather easy to see with the eye alone in a dark sky.
Binoculars may come in handy, though. When the twosome first rises into your southeast sky, the extra thickness of Earth’s atmosphere near the horizon may blur or extinguish the view of the morning couple. Or, if you get up too late, the early morning twilight may wash them out. However, if you see Mars but not Zubenelgenubi, aim binoculars at Mars to reel Zubenelgenubi into visibility.
Even if you can spot both Mars and Zubenelgenubi with the unaided eye, you may still want to use binoculars to check out Zubenelgenubi. Binoculars reveal that Zubenelgenubi is double star – two stars in one. It is believed that these two stars are physically related, so Zubenelgenubi is probably a binary star – two stars revolving around a common center of mass.
Mars travels eastward in front of the constellation Libra the Scales all through December 2019. On December 10, 2019, Mars is heading in the direction of Zubenelgenubi; by December 14, 2019, Mars is definitely moving away from Zubenelgenubi. Midway between these dates – on or near December 12, 2019 – Mars passes a scant 1/5th of one degree to the north of Zubenelgenubi. (For reference, the width of your little finger at arm’s length spans about one degree of sky.)
Bottom line: This next week, before dawn, watch as the red planet Mars sweeps by Zubenelgenubi, the constellation Libra’s alpha star.
Bruce McClure has served as lead writer for EarthSky's popular Tonight pages since 2004. He's a sundial aficionado, whose love for the heavens has taken him to Lake Titicaca in Bolivia and sailing in the North Atlantic, where he earned his celestial navigation certificate through the School of Ocean Sailing and Navigation. He also writes and hosts public astronomy programs and planetarium programs in and around his home in upstate New York.