Even with just the Russian-built module called Zarya ("Dawn") and the U.S.-built Unity docking node joined together, the International Space Station already ranks among the largest spacecraft ever launched. Throw in a visiting space shuttle orbiter, like Atlantis, and you've got a giant, high-flying collection of hardware that is remarkably easy to spot from the ground.
The combined spacecraft look like a bright, slowly moving star when they pass overhead in a dark sky after sunset or before dawn. Orbiting about 220 miles (350 km) up and traveling five miles (8 km) per second, the clustered craft take three or four minutes to cross the sky in a generally west-to-east direction. When Atlantis and the ISS are flying in close formation before or after being docked, they may appear as a slowly moving "double star," or they may appear to chase one another across the sky a minute or two apart.
Since it travels in an orbit inclined 52 degrees to Earth's equator, the space station periodically drifts over most populated landmasses, including all of the continental United States and much of Europe. Atlantis' servicing mission this week and next offers many good viewing opportunities in the evening, especially for locations at relatively high latitudes.
