Every year around the time of the summer solstice, the International Space Station (ISS) remains in near constant sunlight for several weeks, never dipping into Earth’s shadow as it orbits the planet once every 92 minutes. From our landlubber perspective, each time the ISS makes a pass, it does so in sunlight. Passes start just after sunset in evening twilight and last till dawn. From some locations, up to six flyovers a night are visible now through early-mid June.
I saw two last night, the first starting at 10:17 p.m. and the second at 11:54. I could have stayed up for the 1:31 a.m., 3:07 a.m. and 4:44 a.m. passes, but I had to work today. That’s why these special solstice times are called ISS marathons. If you’d like to participate all you need is a clear sky and the stamina to stay up all night.
While you and I revel to multiple flyovers, the half-dozen astronauts occupying the space station experience the “midnight sun” — 24 hours of daylight with the sun describing a big circle in the sky. This special circumstance occurs twice each year: now for the northern hemisphere and in November-December for southern hemisphere skywatchers.
We see all satellites by reflected sunlight. After the sun has set for an observer on the ground, and the sky twinkles with the first stars, sunlight still illuminates mountaintops and satellites which stand at higher altitudes. When watching for the space station, face west and look for a bright, moving “star.” The ISS always rises in the west and travels east across the sky, taking about 5-6 minutes to travel from horizon to horizon.
If you watch carefully, you’ll notice that it’s fainter at first not only because it’s 250 miles high but because it’s also further off in the distance. By the time it’s passing above you, the station is much closer and therefore brighter, too. But the brightest phase comes after it’s passed to the east of south. Then, it’s approximately opposite the sun in the sky and fully lit by the sun the same way the full moon is. Shortly after, it begins to fade again.
During last night’s first pass across the southern sky, it became much brighter — almost equal to Venus — as it slid east of south. Like someone turned up the dimmer switch!
To find out when to see the space station, try Heavens-Above , one of my favorites. Select a city under the Configuration heading, then click the ISS link, and you’ll get a list of passes for each night. Click on the date for a basic map showing the station’s path across the sky. Lots of people like the e-mail alerts from NASA’s Spot the Station. Or you can use a free app for your mobile phone like ISS Spotter for iPhone and ISS Detector for Android.
Watching the space station is lots of fun. You can observe it with the naked eye, binoculars and even a telescope. To see its shape — it looks like the letter H because of the solar arrays — catch it early in the western sky when it appears to move more slowly. I note the direction of the ISS in my low power, wide-field finderscope and then offset the crosshairs to where the station will be in a few seconds. Then I quickly return to the eyepiece and go along for the ride. A low magnification, wide-field eyepiece is best, around 60-power.
I’ll be cheering you on on the sidelines, hoping you’ll complete your first ISS Marathon!