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December 1: Ganymede and its shadow transit Jupiter
December 2nd opens with Ganymede’s shadow transiting the gas giant’s cloud tops. By 4:18 A.M. EST, the shadow finally reaches the western limb and begins its egress. Ganymede finally moves onto the disk not long after, at 4:44 A.M. EST. The large moon will take more than three hours to cross Jupiter’s disk. Observers in the Eastern and Central time zones will see the Sun rise with Ganymede still making its way across; the moon finally ends its transit as the Sun is rising across the Mountain time zone.
The colorful double star Albireo in Cygnus the Swan is a summertime treat. Although different constellations now grace our year-end sky, there’s a similar jewel visible on December evenings in the constellation Canis Major the Big Dog.
Most famous for its brightest star, Sirius (Alpha [α] Canis Majoris), Canis Major is home to many other worthy sights. One is 145 CMa, a lovely double star also called the Winter Albireo for its resemblance to the eponymous pair. 145 CMa is located near the hindquarters of the Big Dog, to the lower left of bright Sirius. Around local midnight tonight, the entire constellation is visible in the southeast, with blazing Sirius well on display. From Sirius, drop down about 11° to find 2nd-magnitude Wezen (Delta [δ] CMa). From this star, move about 3.6° northeast to 145 CMa.
Shining with a combined magnitude of 4.8, 145 CMa consists of a magnitude 5.0 primary and magnitude 5.9 companion. They are separated by almost 27”; Astronomy contributor Phil Harrington says he can regularly split them in 16×70 binoculars. Any small scope should also do the trick.
The reason for their name is the pair’s contrasting colors: The brighter primary shines with a distinct golden hue, while the fainter secondary appears blue-white.
Sunrise: 7:04 A.M.
Sunset: 4:35 P.M.
Moonrise: 2:34 P.M.
Moonset: 4:14 A.M.
Moon Phase: Waxing gibbous (95%)
*Times for sunrise, sunset, moonrise, and moonset are given in local time from 40° N 90° W. The Moon’s illumination is given at 10 P.M. local time from the same location.
