Now that the space shuttle Discovery has left the international space station behind, skywatchers across much of the United States and southern Canada are in for a real treat on Wednesday evening.
Weather permitting, there will be a few opportunities to see both the Discovery orbiter and the space station flying across the sky from many locations.
The sight should easily be visible to anyone, even from brightly lit cities.
Other satellites too
The appearance of either the space shuttle or the space station moving across the sky is not in itself unusual. On any clear evening within a couple of hours of local sunset and with no optical aid, you can usually spot several orbiting Earth satellites creeping across the sky like moving stars. Satellites become visible only when they are in sunlight and the observer is in deep twilight or darkness. This usually means shortly after dusk or before dawn.
What makes the upcoming passages so interesting is that you'll be able to see the two largest orbiting space vehicles in the sky at the same time.
Discovery pulled away from the space station on Tuesday afternoon but should remain within a relatively close distance until it makes its descent to NASA's Kennedy Space Center in Florida on Thursday.
What to expect
Both vehicles are traveling across North America on southwest-to-northeast trajectories.
Appearing as a pair of very bright "stars," the space station should appear as the somewhat brighter object, trailing Discovery as they both move across the sky. A large telescope would be needed to make out details of the sprawling station. Traveling in their respective orbits at approximately 18,000 mph (29,000 kilometers per hour), both should be visible anywhere from about one to five minutes (depending on the particular viewing pass) as they glide with a steady speed across the sky.
Because of its size and configuration of highly reflective solar panels, the space station is now, by far, the brightest human-made object currently in orbit around the Earth.
NASA's 10 greatest science missions On favorable passes, it approaches magnitude -5 in brightness, which would rival the planet Venus and is more than 25 brighter than Sirius, the brightest star in the night sky. Some have even caught a glimpse of the space station just prior to sunset or shortly after sunrise. And as a bonus, sunlight glinting directly off the solar panels can sometimes make the station appear to flare briefly in brilliance.
Region of visibility
Generally speaking, the tandem will be visible across southern Canada and most of the 48 contiguous United States (Hawaii and Alaska, unfortunately, will not have favorable viewing passes during this upcoming week).
Across southern Canada as well as the Pacific Northwest, Northern Plains and Northeast states, there will be three, and in a few cases, as many as four evening viewing opportunities.
Over California, the central Rockies, the Midwest and the Carolinas, there will be two opportunities, while over the Desert Southwest and Deep South, the viewing options are reduced to just one.
When and where to look
So what is the viewing schedule for your particular hometown? You can easily find out by visiting one of these three web sites:
Each will ask for your zip code or city, and respond with a list of suggested spotting times. Predictions computed a few days ahead of time are usually accurate within a few minutes. However, they can change due to the slow decay of the space station's orbit and periodic reboosts to higher altitudes. Check frequently for updates.
Another great site is this one, which provides real-time satellite tracking and shows you at any given moment during the day or night over what part of the Earth the space station or shuttle happens to be.
This report was updated by msnbc.com.
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