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December 16: Titan and Tethys dance
The morning sky brings a lovely scene as the crescent Moon joins bright Mercury in the southeast before sunrise. The pair stands 10° apart in the predawn sky, about 9° above the horizon by 6:45 A.M. local time. The Moon is in southeast Libra, visible as a 6-percent-lit waning crescent at this time with only a sliver of its western limb illuminated. Our satellite sits to the upper right of Mercury; the planet is in far eastern Scorpius, preparing to move into Ophiuchus (where it will reside by tomorrow morning). For now, the claws of Scorpius sit between the Moon and Mercury.
Through a telescope, magnitude –0.5 Mercury appears 6” wide and is 82 percent illuminated. If you have a clear southeastern horizon, keep an eye out for Antares, Scorpius’ 1st-magnitude alpha star, as it rises around 6:30 A.M. some 6.5° to Mercury’s lower right.
The Moon will pass south of Mercury and Antares tomorrow morning, a few hours before Mercury passes north of Antares during the daytime.
Sunrise: 7:14 A.M.
Sunset: 4:35 P.M.
Moonrise: 2:14 A.M.
Moonset: 1:10 P.M.
Moon Phase: Waning crescent (3%)
*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.
Revisit the morning sky December 18 to compare it with yesterday and see just how dynamic our solar system can be. Mercury rises this morning around 6 A.M. local time, with the Moon following later around 6:20 A.M., just after Scorpius’ heart, the red-hued star Antares.
The Moon is now just 2 percent lit — potentially a challenge to view with the naked eye, but its slim crescent should look lovely though binoculars or a telescope. Look for earthshine lighting up the darkened regions of the nearside, as sunlight bounces off Earth and illuminates the portions of the Moon already experiencing night.
Magnitude –0.5 Mercury is now nearly 7° to the Moon’s upper left, in far southwestern Ophiuchus. The planet is now 84 percent lit; a small change from yesterday.
