Wednesday, May 22, 2013
By BERNIE REIM
February is named after februa, which are rites of purification. We will be halfway through winter on the second of the month – Groundhog Day.
Sky Guide: This chart represents the sky as it appears over Maine during February. The stars are shown as they appear at 9:30 p.m. early in the month, at 8:30 p.m. at midmonth and at 7:30 p.m. at month’s end. Jupiter is shown in its midmonth position.
Prepared by George Ayers
Like most months, this month will have its share of good conjunctions. But something much more unusual also will happen.
On the 15th, a little asteroid will make big news. At least it won't make a big impact or a big splash.
Named 2012DA14, this asteroid is about 150 feet across and the size of a gymnasium. It will pass within just 18,000 miles of our surface, which is 13 times closer than the average Earth-moon distance. At our escape velocity, that is only one hour away. At our orbiting speed of 67,000 miles per hour, that is only about 15 minutes away. That means that if that asteroid were to get here just 15 minutes earlier, it would actually crash into the earth.
As it is, this marks the closest approach of a natural object ever predicted far in advance. It will zip across our sky from the South Pole to the North Pole in just 12 hours that night, but it will be too faint to see without a telescope, and even then will be very hard to find because it's moving so fast.
If this little asteroid hit us, it would only release about 3 megatons of energy, or about a quarter of the energy that the comet or asteroid that exploded in the air just above Tunguska, Siberia, on June 30, 1908. That would be nearly harmless unless you were within a close radius. It would probably not even create much of a tidal wave.
That reminds me of a potentially much more dangerous asteroid that came close to us on Nov. 8, 2011. That one was named 2005YU55 and was about 10 times larger, but also passed us at about 10 times farther away than the little one on the 15th.
That one was also moving very fast, about 30,000 miles per hour, but we did manage to find and photograph it through one of our big telescopes at the Starfield Observatory in Kennebunk after several hours of effort.
The size of an aircraft carrier, this nearly round primordial rock was spinning lazily and effortlessly once every 20 hours. By comparison, the huge planet Jupiter, which is 10 times the diameter of Earth, spins around madly once every 10 hours.
It was very eerie to think carefully about what we were really watching that night for several hours. This dark and dangerous chunk of ancient rock had great potential power to harm us, yet it was totally harmless as it drifted along unfettered through space. Scientists got some great pictures by bouncing radio echoes of it with the Gladstone and Arecibo radio telescopes. If it had hit us, it would have caused some real damage by releasing 4,000 megatons of energy and creating a 70-foot tidal wave if it hit the ocean.
There are two comets that might become fairly bright this year. Comet PanSTARRS, discovered in June 2011 by the PanSTARRS sky survey project in Hawaii, could get as bright as second magnitude by the middle of next month. It is already visible in the southern hemisphere.
Then there is Comet ISON discovered in Russia in September of last year. It's still out past Jupiter and visible only in good telescopes now at 15th magnitude in Gemini. It could brighten to 11th magnitude by the middle of August and reach seventh magnitude, which would bring it within reach of binoculars by late October.
Then it should become visible without binoculars by early November and even sport a 10 degree-long tail just before it plunges in toward the sun on Nov. 28. This will be a sun grazer, getting within the radius of the sun. Many comets burn up when they get that close, like Comet Elenin last year, but others survive the perilous journey and emerge on the other side, like Comet Lovejoy. Comet ISON will probably survive. Just before dawn by the middle of December, this comet could become nearly as bright as the full moon and have a tail spanning over 45 degrees of the sky!
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