Jam-packed skies offer plenty of celestial treats this week for stargazers, from a comet snuggling with a galaxy to the moon courting a maiden.
Jovian shadows. Night owls will see a double moon shadow crossing Jupiter's disk in the early morning of Tuesday, December 16.
From 1:12 to 2:02 a.m. EST that morning, the tiny round silhouettes of both Io and Europa will appear through backyard telescopes to slowly transit the face of the giant planet. It's amazing to think that all this action is taking place some 435 million miles (700 million kilometers) from Earth.
Moon and Spica. Early risers on Tuesday, December 16, can check out the moon parked above and to the right of Spica, the lead star in the constellation Virgo, the Maiden. The blue-white stellar giant resides 260 light-years from Earth and can be seen in the morning twilight about eight degrees from the moon. (That's equal to the width of your fist held at an arm's length.)
By Wednesday morning, the moon will have slid closer to Spica but jumped onto its other side.
Virgo galaxy. Also on Tuesday, December 16, telescope users in more southerly latitudes can use the moon to hunt down the elliptical galaxy NGC 4697.
Lying some 40 million light-years away, this giant island of stars shines at a feeble 9.9 magnitude and looks like a tiny, hazy oval patch through the eyepiece under dark skies. Astronomers with the Hubble Space Telescope have recently shown there may be a supermassive black hole lurking at its center, weighing in with as much mass as 100 million suns.
Comet and galaxy. In the early evening of Wednesday, December 17, telescope users get a chance to catch a stunning close encounter between comet PANSTARRS (C/2012 K1) and the galaxy NGC 55.
The comet will appear only one degree from the edge-on galaxy that lies 7.5 million light-years away and spans some 70,000 light-years across. While the galaxy shines at eighth magnitude, the comet is about one magnitude fainter, making it a bit trickier to spot.
Lunar triple play. Early risers on Thursday, December 18, get a chance to see Saturn, the moon, and Spica form a straight line.
Moon and Saturn. By dawn on Friday, December 19, the waning crescent moon will be perched less than 5 degrees above the ringed planet.
Jovian eclipse. In the late evening of Saturday, December 20, Jupiter's moon Callisto will appear to cover its neighbouring moon Io.
Between 10:13 p.m. EST and 10:32 p.m. EST, dimmer Callisto will appear to eclipse the volcanic moon Io.
December solstice. On Sunday, December 21, at 6:03 p.m. EST, the sun reaches its farthest point south in the sky, marking the start of winter in the Northern Hemisphere and of summer in the Southern Hemisphere.