Moon, Mercury to meet up in Taurus
These next several mornings – July 5 to 8, 2021 – watch for the waning crescent moon to travel in front of the constellation Taurus the Bull. The moon’s position will change from day to day, as the shrinking crescent flits by the Pleiades star cluster, then the bright star Aldebaran, and then the bright planet Mercury.
Although Mercury is actually a touch brighter than Aldebaran, Aldebaran will probably be the easier of these two star-like objects to spot. That’s because Aldebaran rises before Mercury does, enabling you to view Aldebaran in a darker sky. Even when Mercury and Aldebaran are both above the horizon, Mercury will be sitting deeper in the glow of twilight, and likely harder to see. Remember, though, that the illuminated side of lunar crescent points to Mercury’s place near the horizon, and binoculars help out immensely in your hunt for Mercury!
We give you Mercury’s approximate rising time at various latitudes for the next several days, given an absolutely level horizon.
40 degrees north latitude: Mercury rises about 1 1/3 hours (1 hour and 20 minutes) before sunrise
Equator (0 degrees latitude): Mercury rises 1 1/2 hours (1 hour and 30 minutes) before sunrise
35 degrees south latitude: Mercury rises 1 2/3 hours (1 hour and 40 minutes) before sunrise
At mid-northern latitudes, you will probably have to be up quite early, or at least 1 1/2 hours before sunrise, to view the glorious Pleiades cluster in a dark sky. In either the Northern or Southern Hemisphere, dawn’s first light (start of astronomical twilight) precedes sunrise a maximum amount of time at and around the summer solstice.
Beginning of astronomical twilight at various latitudes (late June/early July)
40 degrees north latitude: Astronomical twilight begins 2 hours (120 minutes) before sunrise
Equator (0 degrees latitude): Astronomical twilight begins 1 1/4 hours (75 minutes) before sunrise
35 degrees south latitude: Astronomical twilight begins 1 1/2 hours (90 minutes) before sunrise
Find out when astronomical twilight begins in your sky via Sunrise Sunset Calendars, remembering to check the astronomical twilight box.
The sky doesn’t need to be quite as dark to see Aldebaran, the constellation Taurus’ brightest star, or Mercury, the innermost planet of the solar system. From most places worldwide, Aldebaran will rise before the start of astronomical twilight. We exclude far-northern temperate latitudes, where the midnight twilight allows for no true nighttime at this time of year.
From temperate latitudes in the Northern Hemisphere, Mercury will rise after the start of astronomical twilight; whereas in the Southern Hemisphere, Mercury will come up before the start of astronomical twilight. Moreover, Mercury will rise sooner before the sun at more southerly latitudes, giving the advantage to the Southern Hemisphere for this particular apparition of Mercury in the morning sky.
Despite the lengthy morning twilight at northern temperate localities, mid-northern latitudes should still enjoy a fine view of the early morning sky. From around the world – except at far-northern latitudes – watch as the waning crescent moon swings by the Pleiades star cluster, the bright star Aldebaran and the bright planet Mercury.