With NASA's space shuttle Discovery now headed home from the International Space Station, skywatchers across much of the United States and southern Canada are in for a real two-day treat: the last chance to see Discovery in space with their own eyes.
Discovery left the space station today (March 7) and is due to land in Florida on Wednesday. This means that — weather permitting — there are opportunities to see both Discovery and the space station flying across the sky from many locations.
The sight should easily be visible to anyone, even from brightly lit cities. Discovery and the space station should appear as bright, fast-moving lights across the sky. [Photos: Spotting Space Shuttles from Earth]
If you have a chance, these skywatching opportunities aren't to be missed. After this mission, which is the final flight of shuttle Discovery, there will only be two more (one each by the shuttles Endeavour and Atlantis) before NASA retires its space shuttle fleet later this year.
What to expect
Both vehicles will be traveling across North America on northwest-to-southeast trajectories.
Appearing as a pair of very bright "stars," the space station should appear as the somewhat brighter object and will be trailing Discovery as they move across the sky. The pair should appear about 10 degrees apart on Monday evening (your clenched fist held at arm's length measures roughly 10 degrees) so expect Discovery and the station to be separated by about "one fist."
But that relatively small gap between the two will likely widen considerably so that by Tuesday evening Discovery will appear about 1-minute ahead of the space station.
A large telescope would be needed to make out details of the sprawling station. Traveling in their respective orbits at approximately 17,500 mph (28,163 kph), 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 man-made object currently in orbit around the Earth.
On favorable passes, it approaches a magnitude -5 in brightness on the reverse scale used by astronomers to measure the brightness of night sky objects. A magnitude of -5 would rival the planet Venus and is more than 25 times 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 briefly flare with brilliance.
Other satellites visible 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 Earth-orbiting satellites creeping across the sky like moving stars. [How to Spot Satellites in Space]
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 prospective 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, or within several minutes of each other.
Discovery undocked from the space station at 7 a.m. EST (1200 GMT) today. The shuttle flew around the space station before finally pulling away from the orbiting laboratory, although Discovery should still remain at a relatively close distance to the station until the scheduled landing at the Kennedy Space Center in Florida on Wednesday, March 9 at 11:57 a.m. EST (1457 GMT).
Region of visibility
Generally speaking, the tandem will be visible across southern Canada and most of the northern and central United States.
Across southern Canada and the northern half of the United States there will be two or three evening viewing opportunities. For some favored locations, like Denver and Detroit, there will be two opportunities on Monday (March 7).
In contrast, over the Deep South, below latitude 30 degrees north, the viewing opportunities will be reduced to just one or none at all. Places like Miami, New Orleans and Mobile, Ala., will unfortunately be denied a view of the "dynamic duo," because they'll appear too low in the sky and too near to sunset to be easily visible.
Meanwhile, other southern locales such as Houston, Natchez, Miss., and Jacksonville, Fla., will get their one and only chance on Tuesday evening. In most cases, southern observers will have to look quick: Discovery and the space station won't get much higher in the sky than 20 degrees above the horizon, and each will be in the sky for only about a minute (or less).
Some northern localities will be favored with exceptionally good views.
From Boston, for instance, on Monday evening the ISS and the shuttle will appear to soar to an altitude of 87 degrees … virtually overhead … during a two-minute overfly beginning at 6:59 p.m. EST (2359 GMT).
Europe can see Discovery too!
Europeans will also be favored with views in their evening skies.
Paris, for instance, will get two opportunities to see Discovery and the space station on Monday and Tuesday evening. The best of these will come on Tuesday night beginning at around 7:15 p.m. Central European Time (1815 GMT).
Discovery will appear in the west-southwest part of the sky, quickly reaching a maximum altitude of 46-degrees up in the south, then taking another minute to glide over toward the southeast horizon before finally disappearing from view in the Earth's shadow. The station will follow along the same path one minute later.
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 websites:
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.
NASA's space shuttle Discovery is returning to Earth to end a 13-day mission that delivered a new storage room and humanoid robot — called Robonaut 2 — to the International Space Station. Two spacewalks were performed during the mission.
Discovery's current STS-133 mission is the 39th and final flight of the shuttle. Discovery is NASA's most-traveled shuttle and has flown the most missions of all three shuttles still flying today.
Joe Rao serves as an instructor and guest lecturer at New York's Hayden Planetarium. He writes about astronomy for The New York Times and other publications, and he is also an on-camera meteorologist for News 12 Westchester, New York. Click here for shuttle mission updates and a link to NASA TV.