If and when we get a crystal clear night around here, if you look up at just the right time, you might a tiny flashing light moving slowly across the sky.
But it's not a plane's beacon. It's NASA's nanosatellite NanoSail-D -- the first solar sail ever to orbit Earth.
According to Spaceweather.com, observers in Europe have sometimes seen the bright light on the order of a 1st magnitude star, which is bright enough to be easily seen with the naked eye. NASA says one of the sail's main missions is to "demonstrate and test the de-orbiting capabilities of a solar sail for possible use in de-orbiting decommissioned satellites and space debris."
The "flashing" appearance comes from the way the sail tumbles in its orbit and reflects the sun's light.
The sail has been in a steadily decaying orbit and thus, has been getting steadily brighter as it gets closer to Earth. NASA figures it'll burn up upon reentry sometime between this summer and early winter.
In the meantime, you can track the sail and when it will glide overhead. In the short term for Seattle, there aren't too many bright passes, and as usual this spring, clouds are making it difficult to spot orbiting objects anyway. If the clouds do part, the sail is visible just after midnight this weekend, but isn't making any really bright passes yet.
But you can go to spaceweather.com/flybys to get the schedule for when the sail -- and other major orbiting objects of interest can be seen -- including the Space Shuttle Endeavour and the ISS. That pair will be making some very bright passes this weekend and into early next week.
To decode that chart, "Max elevation" is the angle above the horizon at which the sail will make its greatest pass. So 90 degrees means it'll pass straight overhead; 45 degrees means it'll be halfway up, etc. magnitude is a measure of brightness -- the lower the magnitude, the brighter the object. Negative magnitudes mean very bright. Human eye can see to about +6, but the closer to zero, the better.
Happy sail hunting!