The Free Press, Mankato, MN


September 1, 2011

Starline: Three bright planets in morning September sky

MANKATO — This September you can see three bright planets in the morning sky just before sunrise, about 6:35 a.m. at the beginning of September.

About 45 minutes before sunrise, Mercury is visible 7 degrees (fourteen apparent moon diameters) above the east point on the horizon but you will need a clear horizon to see it. Mercury will look like a bright white star.

Be one of the few people who have seen Mercury in the sky.  About 30 degrees above Mercury, but not as bright as Mercury, is blood-red Mars. To the right of Mars is the familiar constellation Orion. Don't mistake the bright red star Betelgeuse in Orion with Mars.

And almost 60 degrees above the southern horizon is brilliant Jupiter, the brightest of these three planets. Low on the southeast horizon is the very bright star Sirius. Don't confuse it with one of the planets.

Last Sept. 8 two small asteroids passed close to the Earth with very little warning. The asteroid designated 2010 RX30, about 15 meters long, came within 248,000 kilometers of the Earth. That is closer than the moon whose average distance is 384,000 kilometers.

The second slightly smaller asteroid, 2010 RF12 came within only 79,000 km. These asteroids were discovered only a few days before the close encounter. But this encounter was small potatoes compared to what might be coming in September 2082. A very larger asteroid, 1999 RQ36 will have a nearly one in a thousand chance of hitting the Earth September 24, 2082.

This asteroid is thought to be about 500 meters across. If it hits the Earth a major disaster would result. NASA plans a visit to this asteroid and if it does threaten to impact the Earth there is time to deal with it. 

The general strategy to deal with asteroids that threaten the Earth is not to blow them up because that probably wouldn't work, but to try to change their orbits. Whatever method you use to deal with these asteroids it is most important to identify them early and that's a job for astronomers.

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