February 24, 2013

What's Up in March: A month for reflecting on the danger of asteroids


The month of March is named for Mars, the Roman god of war. Last year Mars was also at opposition during March, but this year Mars is nearly at conjunction on the other side of the sun, which means it is now nearly at its smallest and faintest for its 26-month cycle. The red planet will not be visible in March at all, and it is nearly five times farther away than it will be at its next opposition in April 2014 when it will get within 57 million miles of us, and appear many times larger and brighter than it does now.

click image to enlarge

This chart represents the sky as it appears over Maine during March. The stars are shown as they appear at 9:30 p.m. early in the month, at 9:30 p.m. at midmonth and at 8:30 p.m. at month’s end. Jupiter is shown in its midmonth position. To use the map, hold it vertically and turn it so that the direction you are facing is at the bottom.

Sky Chart Prepared by George Ayers

The highlights for March will pale in comparison to all the excitement that happened during the middle of last month with the little asteroid that almost hit us, and the unrelated and unpredicted and much more dangerous rain of meteors that did hit us in several locations across the Earth just before and after 2012DA14's closest approach.

The largest of those pieces was about 20 meters across or the size of a school bus or a house. It probably weighed around 10,000 tons and it exploded about 30 miles above the ground over Chelyabinsk, Russia, with the force of half a megaton of TNT, or about 30 Hiroshima atomic bombs detonating all at once. It is a good thing that it exploded that far up so that only smaller fragments actually hit the earth, but the bad part is that the explosion generated an enormous shock wave that caused so much damage because it happened right over a city of a million people with a lot of buildings and glass to damage, injuring more than 1,000 Russians. The biggest fragment hit a lake, creating a 30-foot hole in the ice. That size asteroid hits us on the average once every 40 years.

That event was very similar to one that happened only 1,000 miles farther east and less than 105 years earlier. That was the mysterious Tunguska asteroid or comet fragment, about 100 meters across that exploded about five miles above that part of Siberia with a force at least 20 times more powerful. That blast leveled nearly 100 million trees over a 1,000-square mile area even though no fragments were ever found.

There are two important new projects planned that will greatly help us find asteroids like this in the future before they find us. One is named neocam, which is a proposed space telescope that will see the sky in infrared light. The other one is called B612, founded by two former astronauts. They are trying to raise $100 million to launch a satellite called Sentinel by 2018 that will look back across Earth from near the orbit of Venus.

There are about 5,000 potentially hazardous asteroids that cross over the earth's orbit. Only about 20 percent of them have been found, but 90 percent of the larger ones over 10 kilometer have already been found. They are using Earth-based telescopes like PanSTARRS, NEAR, and LINEAR to find these extremely dangerous chunks of primordial rock and iron.

Spring in the northern hemisphere always starts in March. This year the vernal equinox happens at 7:02 a.m. March 20th. That moment is further defined by the sun on the ecliptic crossing over the celestial equator in an upward direction. That day, along with the fall equinox, are the only two days each year that the sun rises due east and sets due west everywhere on Earth except at the poles. Within a few days of the equinoxes are also the only two days each year when the days and nights are of equal length everywhere on Earth except at the poles. They are off by a couple of days due to our elliptical orbit.

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