Asteroids, Meteors and Comets
By Calvin L. Chrisman
February was an exciting month. Earth was passed by a gymnasium-sized asteroid and a Russian city had a close encounter with a meteorite. The two objects were traveling on completely different trajectories and were unrelated – a cosmic coincidence. The asteroid was predicted, tracked and viewable on NASA TV. Although it passed closer to Earth than our geosynchronous satellites, such as DirecTV, it was no threat. The meteorite, on the other hand, was unexpected – a total surprise. It was a once in a hundred year event. We should all be relieved that it did not occur during the Cold War as it could have had nasty repercussions. NASA estimates that the rock was about 10,000 tons and exploded with the force of a 500 kiloton bomb. The force of this blast, over thirty times the force of the Hiroshima explosion, resulted from the pressure caused by the meteoroid’s high speed entry into the Earth’s atmosphere. It was travelling at over 12 miles per second (almost 45,000 miles per hour). The built-up shock wave caused the meteoroid to break up with explosive force, shattering buildings and windows over a wide area. (Confusing terms: the trail of glowing gas we see is called a meteor. The rock that is causing the visible trail is a meteoroid. If it makes it to the ground, it is a meteorite.)
Is the Earth threatened by impacts from objects like this? The short answer is yes. We are constantly bombarded by space rocks ranging from dust particles to the Chicxulub impactor which was 6.2 miles in diameter and believed to have caused the extinction of the dinosaurs. As governments have become more aware of these threats, resources have been devoted to sky survey telescopes and cameras which look for threats that are large enough to cause city-sized destruction to our planet. If detected early enough, there are ways that these objects can be diverted from a direct collision with Earth. One of these telescope arrays is known as the Panoramic Survey Telescope and Rapid Response System (PanSTARRS). If that sounds familiar, it is because this is the telescopic array that discovered the comet that will visit us in March and carries the PanSTARRS name.
Comet PanSTARRS is expected in our western sky in mid-March. Remember, the well-known comet hunter, David Levy, once said: “Comets are like cats; they have tails, and they do precisely what they want.” At this point, the good news is that Comet PanSTARRS has, indeed developed a tail which is visible only through telescopes. As far as doing what it wants goes, the comet is not brightening as hoped, but current predictions are that it will reach third or perhaps second magnitude by the middle of March. This means that it will not be a spectacular naked eye sight, but it will be visible to the naked eye with a little work and that it will be best viewed through binoculars. It will be following the Sun as it sets in the west. The best days to observe will be March 12th through the 24th when the comet will be most visible. On the 12th and 13th, see if you can spot the thin crescent of the new Moon near the comet. Look west thirty minutes after sunset (remember that daylight saving time will be in effect and the Sun will set at 7:30-7:45 p.m. during this time period) and scan the sky with binoculars. On a clear evening, you should see it easily.
March also marks the spring equinox which will occur at 7:02 a.m. on the 20th. The full Moon, known as the Pascal Moon, will occur on the 27th causing Easter to come almost as early as it can on the 31st. Remember to set your clocks ahead on the night of the 10th as we move into Daylight Saving Time.