ASTROBOB: Our favorite satellite is back

A 30-second time exposure of the International Space Station passing above a fine display of northern lights on June 6, 2013. Watch for the ISS now through early October.

Now through early October, northern hemisphere skywatchers can see the International Space Station (ISS) pass over your house, apartment or tent at dusk.

Dusk comes much earlier now as we approach fall. Sunsets are around 7:15 p.m., with dark skies by 8:30-9 p.m. I can’t get over how easy it has become to observe the night sky. No more waiting until 11:30 p.m.

A run of evening ISS passes start with a few low “swipes” across the southern sky, but the altitude and frequency of the passes will increase. On some nights, you’ll see an early pass followed by a second one about 90 minutes later. When the astronauts look down from above, they see a darkened Earth aglow with “campfires” of artificial lighting concentrated in cities across the planet.

Every pass begins with the ISS appearing somewhere low in the western sky and moving east, gaining altitude and apparent speed as it passes over your location.

Because it’s the largest satellite in low-Earth orbit, it’s also the brightest – by far. Depending on the pass, the station’s brightness varies from Vega-bright to nearly as brilliant as Venus.


On the later evening passes, you might see the ISS fade away right before your eyes as it’s eclipsed by Earth’s shadow. Earth’s shadow rises at dusk and with time fills the sky at the 250-mile-high altitude of the space station. When the station moves into the shadow no sunlight reaches it, the reason it quickly fades from view.

Because the space station is traveling at over 17,000 mph around the Earth, the sun rises every 92 minutes, making for 16 sunrises and sunsets every 24 hours.

During the time it’s in Earth’s shadow and cut off from sunlight, batteries keep the station humming. Recently, the six-person crew of Expedition 60 observed space-caused cellular and molecular changes in mice. The rodents’ genetic similarity to humans may provide insights into aging and muscle ailments. Amen!

A typical pass lasts about 5 minutes with the ISS rising in the west and traveling east until it sets in the east – exactly the opposite of the stars – or disappears in Earth’s shadow first.

A small telescope magnifying about 50x will clearly show the orange solar panels. But you have to act quickly to get the fast-moving object in the field of view for a look. It’s worth the trial and error. I’ll never forget my amazement at seeing a shape when I finally bagged it.

Here are a few good ways to stay abreast of the station. Head over to Heavens Above, Click the link, select your city and then tap the ISS link for a list of passes for the coming nights. Click on a date to see a map and timeline.

Or go to NASA’s super-easy Spot the Station site for times, You can sign up there to get email or text alerts whenever there’s a favorable pass over your city.

You can also use apps like ISS Spotter for iPhone or ISS Detector for Android. Both are free, provide times and directions and can even alert you in advance of favorable passes.


Bob King is a photographer, author and amateur astronomer. Read more on his blog at

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