The Sky This Week, 2013 February 19 - 26
Jupiter, with its two largest moons
The Moon brightens the overnight hours this week as she waxes to Full Moon on the 25th at 3:26 pm Eastern Standard Time. February’s Full Moon is popularly known as the Snow Moon or Hunger Moon since it occurs at a time when winter exercises its strongest grip. Luna begins the week high above the head of Orion, the Hunter. On the evening of the 20th she perches between the "feet" of the Gemini twins. On the night of the 24th she rises with the bright star Regulus in Leo, the Lion, and remains within a few degrees of the star all night long.
Last week we were all watching as asteroid 2012 DA14 swept by Earth just over 17,000 miles above Siberia. In last week’s edition of TSTW I mentioned the irony of the planet’s best viewing prospects being located near the site of the 1908 Tunguska impact and how the current object was not going to hit us. Imagine my surprise when I awoke on the morning of the 15th to stories of a brilliant, destructive meteor fall near the city of Cherlyabinsk in western Siberia! It quickly became apparent that the most destructive meteorite encounter since Tunguska had just occurred, and, despite its incredible timing, it had absolutely nothing to do with the asteroid flyby. The Cherlyabinsk object came at us from the direction of the Sun which made it impossible to detect visually by traditional sky-survey methods, and it s relatively small size of 10 to 15 meters would have been nearly impossible to detect by radar with any meaningful lead time. It was a truly random event even though it spawned an incredible coincidence, and it serves as a reminder that our solar system is a very dynamic place that was born out of the violence of colliding worlds. While the damage and injuries sustained in Cherlyabinsk were relatively superficial, had the impactor been the size of 2012 DA14 the results would have been far more catastrophic, and 2012 DA14 is, in the grand scheme of things, a very small asteroid. Fortunately statistics tell us that we’re probably "off the hook" for awhile, since the Earth is also a very small target in space. However, vigilance is still a good practice, and the U.S. Naval Observatory will continue to do its part by supplying the deep-field star catalogs that are used by asteroid-search surveys around the globe
If you missed sighting the planet Mercury at dusk over the past several evenings, you still have a chance early this week. Mercury passed greatest elongation on the 16th and now seems to "hover" about 10 degrees above the western horizon about half an hour after sunset. Unfortunately he begins to fade quite rapidly as he begins his plunge back toward the Sun, so you’ll been binoculars and very clear skies to sight him after the 22nd. By the end of the week he will still be fairly high in evening twilight, but he will have faded to second magnitude and will be lost in the sunset glow. You’ll get another chance to see him near the end of May, however, when he returns to the evening sky with Venus and Jupiter in tow.
Speaking of Jupiter, we are now entering the last few favorable weeks of the giant planet’s current apparition. Old Jove now crosses the meridian around the time of sunset, and while he’s still very high in the early evening you only have a few hours to enjoy a good view of him through the small telescope. By 11:00 pm he is beginning to settle into the turbulent air over the western horizon and good crisp views of his cloud belts and moons will become harder to find. Jupiter now appears about 20% smaller than he did at the height of opposition, but his disc is still larger than that of any other planetary target. Continue to enjoy him while you can.
As Jupiter sets the solar system’s other truly giant planet Saturn rises in the southeast. In another couple of months Saturn will take over as the reigning evening planet, but if you find yourself up before the Sun now would be a good time to track him down and give him a look. Saturn’s ring system is now amply tipped in our direction and offers a glimpse of what has to be one of the most amazing sights in all of Nature. Composed of billions of small chunks of water ice and interplanetary dust, the rings are a laboratory for gravitational physics. A small telescope of four or more inches aperture will show a dark band near the rings’ outer edge. Known as Cassini’s Division, it is the largest of many such gaps in the ring structure, each of which is caused by a gravitational resonance between the planet and its many small moons.