Marco Langbroek
NASA's space shuttle Discovery and the International Space Station are seen in this time-lapse image as they fly over Leiden, The Netherlands, just before the two spacecraft docked on March 17, 2009 during the STS-119 mission. The shuttle is the object slightly fainter and lower in the sky. Movement is from right to left.
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updated 5/17/2011 7:43:27 PM ET 2011-05-17T23:43:27

Skywatchers south of the equator will get a fine opportunity through early next week to watch as NASA's shuttle Endeavour soars overheard on its final mission to the International Space Station.

Both spaceships, once they meet in orbit this week, will appear as a singular bright "star" moving across the Southern Hemisphere sky.

Endeavour launched into orbit yesterday (May 16) from NASA's Kennedy Space Center in Florida and will dock at the space station tomorrow at 6:15 a.m. EDT (1015 GMT). If all goes according to plan, the shuttle will remain docked to the station until late Sunday night, May 29.

Initially, observers south of the equator will have a number of opportunities to see the docked spacecraft during the pre-dawn hours, moving across the twilight sky. But as the 16-day mission of Endeavour continues, skywatchers in locations to the north of the equator will get their chance to spot the linked shuttle and space station, weather permitting, as well.  [Photos of Space Shuttles and Station From Earth]

What you may see
Most 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.

NASA's space shuttle, when flying independently of the space station, appears as a very bright object; almost matching Sirius (the brightest star in the night sky), though nowhere near as dazzling as the International Space Station.

From May 17 through May 29, when Endeavour is docked at the station, the two space vehicles will appear as one as they pass across the sky. However, after they undock late on May 29, they will appear as separate objects during the final days (May 30 to 31) of the mission. [Complete Coverage: Endeavour's Final Mission]

Because of its size and configuration of highly reflective solar panels, the International Space Station is by far the brightest man-made object currently in orbit around the Earth. On favorable passes, its brilliance can rival the planet Venus and is more than 25 times brighter than Sirius. 

Some skywatchers have even caught a glimpse of the 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 to super-brilliance. 

Where to look to see Endeavour and the station
Initially, only those in the Southern Hemisphere will have opportunities to see Endeavour docked at the space station.

From Johannesburg, South Africa and Bogota, Colombia, for instance, there will be passes each morning through May 22. Buenos Aires, Argentina and Sydney, Australia will have chances through May 25; Melbourne, Australia up until May 26. [N.J. Woman Photographs Shuttle Launch From Airplane]

But as the 16-day mission progresses, Endeavour and the station will gradually become available to those north of the equator. Skywatchers in Key West, Fla., will have viewing opportunities from May 21 through May 27, while those in Honolulu, Hawaii, will get their chance between May 22 through 26.

And after May 26 or 27, visibility will be possible for the northern United States and southern Canada, as well as much of Europe and Asia. 

In a way, this final mission of Endeavour will be saving the very best for last, since after undocking on May 29, the shuttle orbiter and the ISS will appear as separate entities as they track across the morning twilight sky. For the northern US and southern Canada, the two spacecraft will be flying closely in tandem on the morning of May 30, in some cases separated by less than the width of a full moon. 

They will be noticeably farther apart ,with Endeavour appearing to "lead" the space station across the sky, on the morning of May 31. We'll have more to say about this later next week, so stay tuned!

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 site 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 happen to be.    

Endeavour's six-man crew is delivering a $2 billion astrophysics experiment to the International Space Station during this spaceflight. The mission is the 25th and final flight for Endeavour before it is retired along with the rest of NASA's shuttle fleet later this year. [Video: Endeavour's Final Launch Into Space]

NASA is retiring its space shuttle program after 30 years to make way for a new exploration plan to send astronauts on deep space expeditions to asteroids or Mars. Endeavour will eventually be put on display at the California Science Center in Los Angeles. Its sister ships will be sent to other museums for final display, too.

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.

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