Worlds Align. Early risers on Tuesday, December 8, can look for the thin, crescent moon in the low eastern sky before dawn to pin down a beautiful lineup up of bright, star-like objects—most of which are planets. Just above Luna is bright Venus, followed by the blue star Spica and faint ruddy Mars. Brilliant Jupiter rounds out the group, hovering above them all.
Comet Catalina. Also on Tuesday before dawn, Venus and the moon act as guideposts to spotting Comet Catalina, formally known as C/2013 US10.
The trio form a triangular pattern that can been seen with binoculars. Over the course of the week, the comet will pull away from Venus, continue to climb higher in the morning sky, and become visible earlier in the overnight hours.
The icy visitor currently shines between magnitudes 6 and 7, just shy of being visible to the naked eye. Backyard astronomers have been taking amazing photos of Catalina and its two widely separated tails. And in the coming week, the comet may brighten by a magnitude or two—so stay tuned.
Double Cluster. After nightfall on Wednesday, December 9, skywatchers with binoculars can hunt down a famous double star cluster in the constellation Perseus.
The W-patterned constellation Cassiopeia points the way towards Perseus, the mythical hero, and the dual star clusters. Draw a straight line down from Gamma Cass and Delta Cass, the two stars on the left side of Cassiopeia, and you will hit what looks like a dense, double knot of stars in Perseus.
Known as the Double Cluster, made up of NGC 869 and NGC 884, this twin gathering of young stars is visible under dark skies to the naked-eye as a small, hazy blob of light. Binoculars and small telescopes reveal the neighboring clusters located side-by-side in the same field of view. Each cluster contains more than 300 young stars, all of which are less than 10 million years old. Both clusters are about 70 light-years wide and lie more than 7,000 light-years from Earth. The brightest members are supergiants shining 50,000 times brighter than our sun.
Counter Glow. Starting on Friday, December 11, and into the next week, look under dark skies before dawn for the elusive sky glow known as Gegenschein, which is German for “counter glow.”
Gegenschein is a faint, circular glowing area in the sky opposite from the sun and is similar to the zodiacal lights, which look like a cone of light in the direction of the sun at morning or evening twilight. The diffuse patch of light of the counter glow is caused by the backscattering of light off dust spread out between planets in the solar system, but it is usually blocked from Earth viewers by light pollution or the moon’s shine. It is best visible when the sky is moonless and the skywatcher is in the dark countryside far from a city.
The counter glow is easiest to spot around local midnight, when sunshine hits the dust particles in space squarely in relation to Earth. This is similar to the uptick in brightness that occurs when a planet is at opposition, or opposite in the sky from the sun. From our vantage point on Earth, Gegenschein appears as a distinctly brighter spot in the sky. Look for a faint, round glow about 10 degrees across, equal to about the width of your fist held at arm’s length.
Geminids Peak. After a week of slowly ramping up, the annual Geminid meteor shower kicks into high gear, reaching its peak in the overnight hours of Sunday, December 13. With the moon out of the way, sky conditions promise to be perfect for this celestial fireworks show.
Every year around mid-December, Earth plows into a cloud of debris left by the comet-like asteroid Phaethon, causing a shower of meteors that appears to come from the direction of the constellation Gemini.
Best views of the peak will be from the dark countryside, far from city lights, with up to 100 shooting stars visible per hour. From suburbs, these numbers are expected to drop to 20 to 60 meteors per hour, depending on local light-pollution levels. But even in urban centers across the Northern Hemisphere, the brightest meteors, called fireballs, should be easily visible under clear skies. The Geminids should produce a few fireballs during the peak hours from local midnight to just before dawn on Monday.