During the next week, a wayward U.S. spy satellite will make passes across North America and western Europe soon after sunset and should be easily visible to the unaided eye.
That's if it doesn't get shot down first.
The falling satellite is named USA 193. It was launched Dec. 14, 2006. It has been described as being similar in size to a school bus and might weigh as much as 10,000 pounds. It carries a sophisticated and secret imaging sensor, but the satellite's central computer failed shortly after launch, never reaching its final orbit, and the Pentagon declared it a total loss in early 2007.
Since then, the satellite's orbit has been decaying — slowly at first. But in recent weeks USA 193's nearly circular orbit has been rapidly lowering. Currently, its altitude is approximately 160 miles (260 km) above the Earth.
Unless a proposed plan by the Pentagon is enacted to shoot down USA 193 during the next week, the satellite could conceivably re-enter the Earth's atmosphere and burn up sometime in mid-March.
Today through Feb. 22, USA 193 will make a number of evening passes over North America and western Europe. It's orbit is inclined 58.5-degrees to the equator, a setup that makes it readily observable from most of the Northern Hemisphere.
During this period, USA 193 will move along a general southwest-to-northeast trajectory and pass over a number of cities in the United States, southern Canada and western Europe.
To spot a specific satellite, you need to know when and where to look.
Predictions for the times and locations of USA 193 are available at the Heavens Above Web site (http://www.heavens-above.com/). Based on this Web site's sighting information, USA 193 will be very favorably placed for observation over a number of large cities, assuming it is still in orbit around the Earth and weather conditions permit.
What to look for
To find satellites, it's also helpful to know how to roughly measure the sky. Your clenched fist held at arm's length measures roughly 10-degrees of the sky. (From the horizon to the top of the sky, the zenith measures 90-degrees.)
From Seattle, a nearly overhead pass is forecast for Feb. 22. And on that same date, London should have a fine pass, with USA 193 arcing as high as 77-degrees (nearly eight fists) above the horizon.
It should be stressed that because of the rapidly changing nature of its orbit, sighting information from Heavens-Above should be checked frequently.
Those who have seen the International Space Station (ISS) flying across their local skies should be aware that USA 193 will appear noticeably fainter, since it's quite a bit smaller than the ISS. Yet, at its brightest, the spy satellite still should rank as bright as the brightest stars, at roughly first magnitude in astronomers parlance.
Also, since the spy satellite is in a lower orbit than the ISS, expect USA 193 to move much more rapidly across your line of sight.