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December 6: Europa and its shadow cross Jupiter
Early-morning observers can catch Mercury just hours before it reaches greatest western elongation from the Sun at 4 P.M. EST. The solar system’s smallest planet now stands 21° west of our star, rising nearly two hours before the Sun.
By 6 A.M. local time, Mercury is about 6° high in the east, amid the stars of Libra. Shining at magnitude –0.4, it should be easy to spot in the still-dark sky, close to the fainter, 4th-magnitude star Gamma (γ) Librae. Through a telescope, Mercury shows off a disk that is 7” wide and 61 percent lit. Pay particular attention to the orientation of the lighting — Mercury appears illuminated from below as it rises, indicating the direction of the Sun as it follows Mercury into the sky.
As always, make sure to put away any optics at least several minutes before sunrise from your location. That time may differ from the one given below.
Sunrise: 7:09 A.M.
Sunset: 4:34 P.M.
Moonrise: 7:35 P.M.
Moonset: 10:10 A.M.
Moon Phase: Waning gibbous (86%)
*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.
