The Sky This Week, 2013 February 12 - 19
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Mercury, with the Moon & Pleiades |
The Moon waxes in the evening sky this week, with First Quarter falling on the 17th at 3:31 pm Eastern Standard Time. By the end of the week she rides high along the ecliptic, passing near bright Jupiter on the evenings of the 17th and 18th. On the evening of the 19th she lies less than a degree south of the third-magnitude star Zeta Tauri, the southern "horn" of Taurus, the Bull.
All eyes are currently focused on a small chunk of solar system debris known as 2012 DA14, which will whiz past the Earth on the afternoon of the 15th. At the time of its closest approach, at 2:25 pm EST, the rock will be about 27,000 kilometers (17,000 miles) above the Earth’s surface. This distance is well within the belt of geostationary communications satellites, but there is no danger of a collision with the planet or any of the expensive hardware parked out there over the Earth’s equator. 2012 DA14 is estimated to range in size from the Space Shuttle to perhaps 50 meters across, but it has considerably more heft than a Shuttle. No object of this size has ever been seen to pass this close to the home planet, so astronomers around the world will be monitoring it as it glides by. Its orbit has brought it within hailing distance in 2004 and 1918, and this will be its last and closest approach for at least the next 75 years. Amateur astronomers in the eastern Northern Hemisphere will have a chance to see the speedy asteroid zip through the northern circumpolar constellations as it makes its brush with Earth. By the time darkness falls in the Washington, DC area 2012 DA14 will be rapidly retreating from us and lost to visibility in all but the largest telescopes. It is a bit ironic that the best place to watch the flyby from is Siberia; in 1908 an object of similar size exploded in the air over the Tunguska River with the destructive power of a two-megaton atomic bomb, flattening trees for hundreds of kilometers in all directions. Thankfully this will not be on the schedule for this event!
From near-earth asteroids we can focus the rest of the week on tracking down the elusive planet Mercury. The innermost of the Sun’s family reaches greatest elongation east of Old Sol on the 16th. This is the peak time to track him down for the year’s best evening showing of this shy world. You should be able to spot him fairly easily in the west-southwest sky about 45 minutes after sunset, where he will be between five and ten degrees above the horizon. Use binoculars to start looking for him at this time; once you’ve spotted him in the glasses you will probably be able to see him with the naked eye. He gains altitude during the course of the week, but he also fades by over half a magnitude as the nights pass. However, once you’ve spotted him he should be fairly easy to find until well into next week.
Bright Jupiter is the bright object that you’ll see high in the south as evening twilight deepens. The giant planet leads the bright stars of the Great Winter Circle across the meridian during the early evening hours. He has begun to move in direct eastward motion against the stars again, and you should soon be able to notice him gradually nearing the bright star Aldebaran. Jupiter’s apparent disc is shrinking as Earth increases the distance from him. At his best during opposition he gave us a generous 48 arcsecond disc to study; that has now waned to 41 arcseconds. This is still much larger than any other object except the Moon, so it’s still worth casting a glimpse his way to keep tabs on his constantly turbulent cloud belts.
In the meantime, Saturn is steadily working his way into the evening sky. As the week opens he rises just before midnight in the southeast. By the end of the month he’ll be up before 11:00 pm. The best time to observe him is still during the pre-dawn hours when he is near the meridian. The view of his magnificent rings and dancing icy moons is well worth the effort to rise before the Sun.
