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Night Sky

November 2010 Night Sky

—Charlie Christmann

Hazards Abound

The threat of an unknown asteroid or comet intersecting with Earth’s orbit has not gone unnoticed. Everywhere we look in the solar system, there is ample evidence for impacts large and small. Just look at our own Moon—it’s full of craters. Recently, there have been several media reports of near misses with asteroids.

The realization, late last century, caught the attention of the U.S. Congress and NASA. In 1998, NASA started the Spaceguard Survey. The idea was to locate 90 percent of the Near Earth Asteroids (NEA) larger than one-half mile in diameter before the end of 2008. In 1998, NASA also created a Near Earth Objects (NEO) Program Office. In 2003, a NASA study showed that it was both technically feasible and cost-effective to expand the Spaceguard Survey, using larger telescopes, to search for smaller asteroids lurking in a near Earth orbit.

Much of the efforts to find and track these Potentially Hazardous Asteroids (PHA) has been conduced in New Mexico near Socorro. There is a program there called the Lincoln Near-Earth Asteroid Research (LINEAR) project. Another telescope located in Hawaii also looks for PHA.

How many have of these potential troublemakers have we found? Scientists think we have seen most of the big ones that can cause catastrophic global damage. It’s the smaller ones that could cause significant local damage that now worry the sky watchers. They believe that we have found around 40 percent of those smaller than one-half mile in diameter.

According to NASA, our warning time before impact could be very short. “With so many of even the larger NEOs remaining undiscovered, the most likely warning today would be zero—the first indication of a collision would be the flash of light and the shaking of the ground as it hit. In contrast, if the current surveys actually discover a NEO on a collision course, we would expect many decades of warning. Any NEO that is going to hit the Earth will swing near our planet many times before it hits, and it should be discovered by comprehensive sky searches like Spaceguard. In almost all cases, we will either have a long lead time or none at all.” [Ref:] But the odds of that happening in any given year are very small: about one chance in 40,000.

This column has already told you of the “big rock” for my wife on our anniversary in 2029. On April 13, 2029, Apophis, about 1,000 feet in diameter, would pass inside the orbit of the geostationary satellites. If its trajectory happened to follow a very narrow corridor, this rock would return in 2036, again on April 13th, with its sights set squarely on Earth. The probability of this happening is again small.

As of October 20, we know of 1,155 PHAs. And we are finding more all the time. Just a year ago, the count was 1078, and two years ago we only knew about 990 PHAs. On October 7, 2008, asteroid 2008 TC3, a rock only 10 feet in diameter, actually impacted us. The reports indicated the meteor mostly burned up in the atmosphere somewhere over northern Sudan. Just recently, on October12, 2010, asteroid 2010 TD54 (discovered October 9) missed Earth by only 23,900 miles. This one was only 23 feet across and would not have caused any damage. And on September 8, 2010, asteroid 2010 RF12, at 30 feet across, missed us by 47,000 miles.

Fortunately for us, NASA does not believe there are any really big asteroids heading our way. Even Apophis has a low risk of impact. So in reality, there is no real need to worry about the recent reports of close encounters with space rocks.

The Planets and Moon

  • Don’t look for Mercury this month; it’s hiding in the sun’s glare.
  • Venus will be appearing in the east before sunrise. Look about 15 minutes before sunrise on the 4th, using binoculars to see a dim, but beautiful thin crescent shape, then even earlier in the morning as the month progresses. Venus will be very bright after the 10th. Look on the 5th for the waxing crescent Moon to be just below Venus.
  • Look low in the west just after sunset for Mars. It will be disappearing into the sun by month’s end. Look for the waxing Moon on the 7th. In the fading glow of the sun, just 25 minutes after sunset, you’ll find Mars 2.5 degrees to the upper right of the Moon. Antares will be on the horizon just below the Moon.
  • Jupiter will be high and bright in the night sky after sunset. On the 15th, look for Jupiter seven degrees to the lower left of the Moon.
  • Saturn rises in the early morning hours this month. Look one hour before sunrise on the 3rd for Saturn 10 degrees to the left of the waxing Moon.
  • Feeling lucky? Try finding Uranus using good binoculars or a telescope. It will be to the upper left of Jupiter. On the 15th, the Moon, Jupiter, and Uranus form a nice tight triangle.
  • The Moon is new on the 6th and full on the 21st.




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