Space station marathon week – an excuse to stay up all night

Time exposure of the International Space Station during a pass across the northern sky. The ISS looks like a brilliant, pale yellow star that moves from west to east. A typical pass takes about 5 minutes. Photo: Bob King

Every early June in the northern hemisphere (December in the southern), the International Space Station (ISS) can be observed on multiple passes from dusk till dawn. Taking only 90 minute to circle Earth, the station is normally visible once or twice a night during twilight, when it catches the sun’s rays 250 miles up and glimmers brightly against a darkening sky.

Passes continue through the night – yep, it’s up there – but we can’t see the football field-sized satellite because it’s in Earth’s shadow. The sun has set for the astronauts; they look out the window and admire the sparkling lights of cities below and stars above.


Video of sunrise and (almost) sunset seen from the space station around summer solstice.

That all changes for a week or two around the summer solstice thanks to our planet’s tilted axis and the highly inclined orbit of the ISS. The space station’s orbit is tipped up at an angle of 51.6 degrees to the Earth’s equator. That means it visible anywhere on the ground between 52 degrees north and south of the equator – a vast region that includes 90% of humanity.

During northern hemisphere summer, Earth’s north pole is tilted 23.5 degrees toward the sun. When combined with the space station’s steep orbital tilt, the ISS manages to avoid Earth’s shadow, remaining in constant sunlight during its entire orbit. For a daydreaming astronaut staring out the cupola windows, the sun never sets. He watches it drop to edge of the globe and then rise right back up again. Watch the video above and you’ll see what I mean.

In the diagram, the circle represents Earth with its north pole tipped sunward around the time of summer solstice. The ISS’s orbit – tipped well up from the equator – is shown in profile. Notice how close the station passes to the day-night line or terminator. This allows it to remain in sunlight its entire orbit. Illustration: Bob King

The diagram will help you picture what’s going on. Earth’s axis points off to the left with the northern hemisphere tilted toward the sun. The terminator is the boundary between day and night on the planet, and the equator cuts perpendicular to the axis. The space station’s tipped orbit places it very near the terminator this time of year, high enough for it to catch the sun’s rays all night long.

For sky watchers that means that virtually every time the station comes over your house this time of year, you’ll see it shining in sunlight even in the middle of the night. Depending on your particular location, five passes a night are possible. Amazing!


Half-minute video of the space station tracked through a telescope

So break out the Cheetos and tea and see how many times you can spot the station in the week ahead. I also encourage anyone with a telescope to try pointing it at the ISS during one of its frequent passes. A magnification of 50x will easily show at least two orange solar arrays sticking out on either side of a shiny, white blob (the space station proper).

Give it a try – you won’t believe it. It’s almost like seeing Saturn for the first time in a telescope. The best way to grab this fast-moving object is to aim the scope a short distance ahead of where you expect the ISS to travel and dart back to the eyepiece asap. You may miss on the first try, but eventually you’ll snag it. Move the telescope to match its motion and study the image for fascinating details. The best views are when the ISS passes nearly overhead. That’s when it’s closest to you and appears largest.

I saw the panels last night during a 2:12 a.m. pass and am looking forward to at least a half-marathon tonight. I’d do the full marathon but hey, I have to work tomorrow.

The ISS orbits about 250 miles above Earth about 18 times a day at an average speed of 17,000 mph (27,000 km). Credit: NASA

For viewing times for your city, log in to Heavens Above or check out Spaceweather’s Satellite Flybys. The former provides great maps showing the satellite’s path. You can also sign up at Spot the Station and have NASA e-mail you anytime there’s a good pass for your location. Be aware however that they only send alerts for the better passes; marginal but still visible ones are not given.

Below are times when the ISS will be visible from the Duluth, Minn. region:

*  Tonight June 2-3 starting at 11:49 p.m. First pass high in the eastern sky starting at 11:49 p.m. Watch for the station to first appear high overhead and move east. Second pass at 1:23 a.m. across the north. Third pass at 3 a.m. across the north.

* June 3-4 – Banner night! First pass at 10:58 p.m. across the south-southeast. Second  at 12:34 a.m. in the northern sky. Third at 2:11 a.m. in the north. Fourth at 3:48 a.m. straight across the top of the sky.

* June 4-5 – Ultimate Marathon Night! First pass at 10:09 p.m. across the southeast. Second at 11:45 p.m. high in the northern sky. Third at 1:22 a.m. in the north. Fourth at 2:59 a.m. in the north. Fifth at 4:36 a.m. in bright twilight in the southwestern sky.

10 thoughts on “Space station marathon week – an excuse to stay up all night

  1. Hey Bob. Thanks for your reply to my comment last night. I did a little research on Calsky and indeed there were (and i’m sure are) a crapload of geostationaries in that part of the sky. impossible for me to exactly narrow it down since i didn’t make a detailed enough observation of the flare’s exact position. Next time i notice something like this i’ll do better! Anyway, this AM i caught the ISS briefly in twilight between 4 and 5 AM. After i initially spotted it i was able to get a brief (10×50) binocular observation. When the sky is bright enough, and the ISS passes close enough, i feel as though i can see darkness on either side of the lit part (main body) of the station. Am i kinda imagining this because i know it has solar panels and am trying to see them, or is there a chance i am legitimately seeing something along those lines with that magnification? This isn’t the first time i’ve noticed this in similar conditions, but i have never been sure if i’m actually observing material or if it’s rather some optical effect enhanced by my brain’s power of suggestion.

    • Sean,
      Yes, that’s a great place to point a scope and “discover” a few. Not sure if you can really see the solar panels on the ISS at 10x. That sounds very low. I saw them again tonight through my 15-inch scope using 64x. They’re fainter, linear and very orange compared to the rest of the space station. Based on how large they appeared I’m going to guess you’d need at least 20x to be sure you were seeing them.

  2. Hey Bob, Ever since I’d first heard about it through the media, I’d been fascinated with the idea of seeing the Shuttle chasing the ISS across the sky or just beginning to lag behind after separation. I was very disappointed the first time I went out to see them “together” and found them half a sky apart. But I finally got lucky and saw the pair very close just after separation and, between them, first noticed in binoculars but also visible to the naked eye, a cloud of…what? Water vapor? Air lost when they uncoupled? Propellant of some sort? I e-mailed my question to NASA but they never responded. Any ideas? Thanks. Norman S.

    • Hi Norman,
      I really miss those cat-and-mouse games the shuttle and ISS would play. The cloud you saw was a water dump better known on Earth as a toilet flush.

  3. hey Astrobob, i work with StarWatch Night Vision Tours (http://starwatchtours.com) and while on tour June 3 near Asheville, NC we caught some interesting video of a very bright (and seemingly very low) object in the sky which appeared to be flying around the cloud level (optical illusion or not?) and we caught some it on NV video:
    http://www.youtube.com/watch?v=AQUSVIPrM5A&feature=youtu.be

    we’re wondering if this might have been the ISS. do you know of any way to confirm this one way or the other?

    thanks! 8-)

    • Hi Bernard,
      I would say it’s almost certainly the ISS. It was visible and very bright (mag. -3.5) that night in Asheville, NC. starting around 10:20 p.m. The flickering or flashing is caused by the varying thickness of the foreground clouds. The ISS typically orbits about 250 miles above the Earth. Does the time jive with your observation?

      • yes, it could have been around 10:30-ish for sure. the thing that seemed odd is that when i first spotted it, there were no clouds in that area of the sky. when it travelled into the area of the sky with clouds, it appeared as though it was going in and out of the clouds, so we thought it was very low. besides that, even by the naked eye it seemed to be very low in general. but again, i understand how all of that could be due to optical illusions, etc. well, this might take much of the fun/mystery out of the spotting and the video, but we certainly want to know the truth of the matter. if you have any other ideas about further confirming that the video we took is definitely the ISS, please advise. thanks! 8-)

        • Bernard,
          Since the ISS was moving relatively quickly and was very bright, it would flash more vividly and make you think it was low as it were going in and out of clouds like a low-flying plane. Both appear superficially similar. If I could positively ID some of the starfields the satellite was passing through, then I could tell you exactly the time the video was shot and absolutely confirm it as the ISS and not some other bright satellite. Still working on that but the brilliance of it makes it nearly a sure bet for the space station.

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