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.
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.
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.