Observing Alert — Space Station Marathon Underway!

Astronaut Jack Fischer waves while attached to the Destiny laboratory during a spacewalk to replace a failed computer relay box and install a pair wireless antennas earlier today. Credit: NASA

Astronauts conducted an emergency spacewalk earlier today to replace a failed computer that controlled the solar power system, radiators and other crucial equipment on the International Space Station (ISS). They had been using a backup, so everything’s thumps up now. I’ve read it’s hard work working in repairs outside the station, but the views are second to none.

The track of the ISS near the bright star Vega in Lyra. From right to left, the station is passing from sunlight into Earth’s shadow. Its color transitions from white to red (daylight to sunset as seen by the astronauts aboard the station). Credit: Bob King

Speaking of views, skywatchers in the northern hemisphere will be treated to great views of the space station multiple times each night as it orbits the Earth 250 miles overhead. Every year at this time, the northern end of the station’s orbital loop remains in full sunlight during each evening pass. From an astronaut’s point of view, the sun never sets. Since it takes about 93 minutes to go around the planet once, that means we get to see a space station pass every 93 minutes from dusk till dawn! For my town, we’ll get a max of five passes. Other locales could see up to six.


See the midnight sun effect at the ISS near the time of  the summer solstice

Normally, only one or two passes are visible at dusk or dawn. While the ISS continues crossing the sky during the night, we can’t see it because it’s hidden from view (eclipsed) by Earth’s shadow. But in late May-early June each year, the space station’s orbit and Earth’s day-night terminator nearly align. From the astronauts’ viewpoint, the sun shine all the time, much like we would see the midnight sun from the Arctic Circle. Back down on the planet between latitudes 40°-55° north, we can see passes all night.

Diagram showing the Earth in late May when the space station’s orbital track is closely aligned with the day-night line on the planet called the terminator. The astronauts see the sun 24-hours a day (midnight sun effect) while ground-dwellers are treated to repeated passes. Credit: Bob King

If the ISS exactly followed the day-night line, it would be in sunlight 24-7, but notice that it’s tilted a little with respect to that line. During the southern hemisphere part of its orbit, it’s only out during daylight and invisible around this time.

You can find out exactly when to look and how many passes to expect for the next couple weeks by checking Spaceweather satellite flybys, NASA’s Spot the Station or Heavens Above (just log in for free, click the ISS icon and then click a date / time for a nifty map of the space station’s path across the sky.) The ISS always begins a pass somewhere in the western sky and travels east with a typical run taking about 5 minutes. It’s very easy to photograph because it shines as brightly as Jupiter. You’ll need a tripod and a camera that can expose for 15-seconds or longer. Get a map of the station’s path from Heavens Above beforehand, so you know where to point the camera. When it enters the field of view, carefully depress the shutter button.

While you may not stay up the entire night to catch all 5 or 6 flybys, know that the ISS provides something for everybody whether you’re out at dawn or dusk. For example, for the Duluth, Minn. region tonight, there will be 5 passes — 9:55 p.m., 11:30 p.m., 1:07 a.m., 2:44 a.m. and 4:20 a.m. Crazy.