Spice Up Your Space Station Watching

The annual International Space Station Marathon is underway with multiple passes visible each night. Here are some fun and unique ways to see and share it. 

ISS spin cycle

The International Space Station enters a special season this month, when it makes passes all night long.
NASA

The International Space Station (ISS) will be your constant companion the next few weeks. The ship and crew of six astronauts will make visible passes for skywatchers in the Northern Hemisphere every hour and a half from dusk till dawn.

If you're game, you can even participate in what satellite watchers informally call an ISS Marathon. Clear skies and a crazed determination to stay awake all night, a trait common among our tribe, are all you need.

Every year in May and June, the space station remains in sunlight, or nearly so, throughout its orbit. From an astronaut’s point of view, the Sun never sets, the orbital equivalent of the Land of the Midnight Sun. For observers in the Northern Hemisphere, the ISS avoids eclipse by Earth's shadow and remains in full sunlight pass after pass. As the ISS circles the planet every 90 minutes, punctual skywatchers can witness up to 5–6 passes each night, the first in evening twilight and the last at dawn.

ISS takes the night off

Around summer solstice, the steeply inclined orbit (51.6°) of the International Space Station, combined with the sunward tip of Earth's Northern Hemisphere, tilt the station's orbital plane nearly face-on to the Sun. For Northern Hemisphere observers, the station sidesteps Earth’s shadow. Astronomers refer to the steep tilt as a high beta angle. Other times of year, when the orbital inclination is less extreme, the ISS passes into the shadow, reducing its appearances to one or two a night.
NASA

Normally, only one or two passes are visible at dusk or dawn with the others eclipsed by Earth's shadow. But around the time of solstice the station's orbit and Earth’s day–night terminator nearly align, and the shiny craft comes round again and again like a ball on a tether.


Around the time of the summer solstice for the Northern Hemisphere and winter solstice for the southern hemisphere, the Sun never sets on the ISS as seen in this video made on board. 

The same situation plays out for skywatchers in the Southern Hemisphere in November–December when that hemisphere is tilted toward the Sun. On Sunday night (May 20th) I caught two ISS passes, the first at 10:17 p.m. and the second at 11:54 p.m. I could have stayed up for the 1:31 a.m., 3:07 a.m. and 4:44 a.m. passes, but work loomed on the 9:00 a.m. horizon.

Swing high sweet ISS

This table and map are from Heavens Above and show the 9:17 p.m. CDT pass on May 23rd for Minneapolis. Time stamps show the station's position at 1-minute intervals. The table lists five passes for that city for May 23rd.
Chris Peat / Heavens Above

To find out when and where to see the space station, try Heavens Above, one of my favorite sites. Select a city under the Configuration heading and you'll get a list of passes for each night. Click on the date for a map showing the station's path across the sky. Lots of people like the email 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. The Sky & Telescope Satellite Tracker gives predictions for upcoming passes, while the Transit Tracker will let you know when the space station comes within 10° of any naked-eye planet, the Moon, or the Sun (or more rarely, when it crosses either Sun or Moon).

Kiss a crow

I took this time exposure of the ISS from Duluth, Minnesota, during its 10:17 p.m. pass across the southern sky on May 20th. The pink color is light pollution. Notice how the trail becomes brighter to the left as the station moves east of south.
 Bob King

The ISS always appears in the western sky first and travels east. Look for a bright, pale yellow star,  with a steady light. When seen at low altitude, the station appears fainter because there's more lateral or horizontal distance between you and the craft. Even then it still shines as bright as Vega. But when it makes a high or overhead pass, it’s only about 250 miles away, as close as it gets, and outshines everything in the night sky except Venus and the Moon.

Northern track

By the time of its second pass on May 20th, the Earth's rotation had shifted the path of the ISS to the northern sky. The streaks are moonlit clouds. 
Bob King

Peak brightness occurs not when the station arrives at the zenith, but some distance beyond it to the east, when the Sun (on the opposite side of Earth) directly illuminates the satellite similar to what happens during a full Moon. For a short time, full illumination compensates for its increasing lateral distance. Similarly, when the ship first appears in the west, its angle to the Sun is slight, so we see a "crescent" ISS. This contributes to its fainter appearance at that time.

Jack be Quick

With so many opportunities for seeing the ISS, you've got time to try out some new tricks. If you've never seen it through a telescope, it's easier than you think. The amazing thing is that you can discern its shape, especially those golden, kapton-insulated solar arrays. I use a wide-field eyepiece with a magnification of 65×. Catch it first when it's low in the west and moving with a slower apparent speed. A low-power finderscope is key here. Aim the finder at the ISS and note its direction of travel, then set the crosshairs at the spot you anticipate the station to reach in a few seconds and quickly return to the eyepiece. Like cupping a leaping frog with your hand, you'll get the knack of it after a couple tries.


This video of the ISS through a telescope hints at the visual impression.

With the satellite in view, pull the scope along to follow, keeping the ISS centered in the field of view as best you can. Sure, it'll be a little herky-jerky, but you'll thrill to the sight during those seconds when you're locked on.

Once you've succeeded alone, get your friends or family to queue up at the eyepiece during another pass. Your job will now be to keep the ISS centered as best you can in the finder while moving the scope to follow. That gives each person an opportunity to look. I've had up to six people spot the ISS during a single pass. It makes for great fun at star parties.

Curve Ball

If you like playing catch, you're going to love tossing the International Space Station around. Last year, I wondered how far apart two observers could be and still view the ISS simultaneously, so I e-mailed my friend Rick, who lives in Port Angeles, Washington, and we hatched a plan.

Our two cities are about 2,350 km apart as the crow flies. Because the station orbits at an altitude of about 400 km, an observer (at sea level) can see it up to about 2,300 km away at setting or rising. We figured that when the ISS stood midway between us — about 1,650 kilometers give or take — Rick should see it dropping off in the eastern sky the same time I'd see it rise in the west.

ISS Pass

This diagram shows a typical ISS pass. Disappearance happens when the ISS is eclipsed by Earth's shadow.
NASA / Spot the Station.

Next, we identified a suitable pass, one we could both see despite being two time zones apart. Since Rick lives in the far west, we selected an early pass for him so that by the time the station arrived over Duluth, it would still be in sunlight. The pass we chose had the ISS reaching maximum altitude at 9:34 p.m. Pacific Time for Port Angeles and 11:39 p.m. Central Time (9:39 p.m. Pacific) for Duluth, just 5 minutes later.

We got on the phone together at 9:30 p.m. PDT. A couple minutes later when my friend spotted the station, it was game on. At 9:35, when the ISS had crossed into the eastern sky for Port Angeles, I caught sight of it clearing the western horizon in Duluth. For 60–90 seconds we watched it simultaneously from 2,350 km apart!

About the time the ISS crossed my meridian, Rick caught a last glimpse in the east. I found the experience exhilarating. For a few moments my distant friend and I attended a live performance together on an Earth-sized stage.

I encourage you to play space station "catch" with a friend or family member. Fire up two Heavens Above tabs — one for each city — and comb through the list to find pass times that occur around the same time (deducting the time zone factor) for the two locations. Call a friend and share an out-of-this-world experience!

9 thoughts on “Spice Up Your Space Station Watching

  1. Joe StieberJoe Stieber

    I’ve seen five (5) ISS passes in a single night several times before, but this recent Monday-Tuesday night, May 21-22, 2018, I finally bagged six (6) ISS passes, despite having to battle some cloudiness for the final four of them. Earlier on Monday, May 21, about 4:49 am EDT, I was able to briefly see, through a gap in the clouds, the second stage rocket plume from the Antares launch out of Wallops Island, VA, carrying the Cygnus OA-9 cargo ship to the ISS. About six minutes after the fifth ISS pass just below Polaris at 3:22 am EDT on May 22, I saw the second magnitude Cygnus following essentially the same track as the ISS in my 15×56 binoculars. All of the ISS passes were visible with unaided eyes for at least part of the pass (clouds obscured portions of the later passes).

    Also, I’ve observed the ISS in a scope before, and indeed I’ve noticed that the solar panels are a golden-bronze color when backlit, like after sunset when the ISS is rising between the observer and the now-set sun. However, they look white to me as seen by reflected light, when the sun is behind the observer’s position. Thanks for the info on Kapton. I’m familiar with it and its color, but didn’t know it was used on the solar panels.

  2. Joe StieberJoe Stieber

    I’m retired now and have flexibility with my schedule, so I napped much of Tuesday. It was quite cloudy Tuesday night, so no observing. Wednesday night, May 23-24, 2018, was clear, so I was able to catch all four of the visible ISS passes with unaided eyes, but the neat thing was seeing the much fainter Cygnus freighter all four times with 15×56 binoculars as it closed-in on the ISS. The first pass was nominally at 8:45 pm in moderately bright twilight and I had to wait for Cygnus to enter the 4.5 degree binocular field after the ISS left. Ditto for the second pass at 10:20 pm, but now it was dark, so I had field stars for reference. I counted 13 seconds between the two passing the same field star. At the midnight pass, both fit in the same binocular field and they were 8 seconds apart. At the last visible pass of the night, about 1:35 am, they both fit in the same binocular field with room to spare and were 5 seconds apart. They would rendezvous at 5:26 am on Thursday, May 24.

    So, I had a brief view of the Cygnus freighter launch on Monday morning, then had a final view of Cygnus on Thursday morning when it was less than four hours from docking!

  3. Tom-Reiland

    We haven’t had much luck with the ISS the past several nights because of the weather or poor passes low in the Northern part of the sky. I have seen the shape of the solar panels through my 10 X 50 binoculars several times, but the biggest surprise I had was when I observed it in the East when it was easy to manually track with the 21″ Reflector at Wagman Obs at 115X several years ago. I could see the panels easily, but I was shocked to see the grids on the panels. The detail was amazing. It’s one of those observations you never forget. I was able to repeat it once, but I haven’t had another chance to try it.

  4. Monicatfp

    Great information. I use a rext for alerts.
    Subject:SpotTheStation
    Time: Sun May 20 11:18 PM, Visible: 6 min, Max Height: 54 degrees, Appears: WSW, Disappears: NE
    (perhaps the information you provide in your article could have been given last month so watchers could have been ready for the fun in May.)

    1. Bob KingBob King Post author

      Hi Monica,

      Sometimes it’s a matter of scheduling with competing events. Since the “ISS Marathon” (continuous evening and morning passes) didn’t begin until about May 21 and would last into June, I figured there wouldn’t much harm in getting the article ready for May 23. But yes, ideally, the week before would have been even better. A month before would be too soon in my opinion — at least for online publication — as I think most folks would have forgotten about it a month later. Thanks for writing — and there are still passes happening all this coming week and most of next.

  5. Tom HoffelderTom Hoffelder

    Having lived in New England for 20 years, I have had some recent yearly opportunities to see the ISS five times in one night in June and/or July. Much to my surprise there are no (none, nada, zero, zip) visible night passes in Maine for the entire rest of June, not a single one! I know this can happen but I don’t think I’ve ever seen it happen in June. July starts to improve, but it isn’t until the end of the month that five passes are visible in one night.

    1. Bob KingBob King Post author

      Tom,

      Same for us in northern Minnesota. It does seem unusual for June, but that’s how the dice roll! Late July is looking great for the next series of multiple passes.

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