The Soyuz TMA-18 launches
Hot on the heels of the Soyuz launch, Space Shuttle Discovery is set to join the fold on Easter Monday as the STS-131 mission gets underway to continue outfitting the station for science operations now that its construction is virtually complete. This is a rare opportunity to catch sightings of human spaceflight hardware in action in the skies as they fly in syncronicity. It always amazes me how surprised people are to hear that you can actually see our man-made satellites as they follow their orbits around the planet during two time windows that occur every day. About an hour before sunrise and an hour after sunset, any satellite that passes overhead within a roughly 300 mile radius will be high enough to still be lit by the Sun, reflecting enough light to be seen from the surface Since their orbits are very predictable - we can pinpoint their position in the sky for months ahead - it is a simple matter of some well developed math to predict when such sightings will occur given any location on the globe.
Spacecraft that launch to the ISS are often seen together in close formation as they approach the outpost, giving the impression that they are following each other across the sky. It is a truly incredible sight to see, and sadly at its best with the much larger Space Shuttle which is set to retire at the end of this year - so catch a glimpse of the orbital syncronized flying while you can.
Enter your location and find the next visible pass for you at http://www.heavens-above.com
Image credit: NASA/Carla Cioffi