While millions will watch the August 21st total solar eclipse from the ground, the International Space Station crew will have an amazing view high overhead.

Umbra from the ISS
The umbra of the Moon as seen from the International Space Station during the March 29, 2006 total solar eclipse.

Less than three weeks lie between us and the first total solar eclipse cross the contiguous United States in 38 years. If you're like us, you've already got a plan (and a backup plan) for the main event on Monday, August 21st. (Observers in eastern Europe,  Africa, and Asia won't miss out completely: they'll see the pre-show event, a partial lunar eclipse on Monday, August 7/8th.)

The path of the August 21st, 2017 total solar eclipse across the United States.
Michael Zeiler / greatamericaneclipse.com

Humans in space will watch as well, as the International Space Station zips 250 miles above Earth's surface, orbiting the planet once every 93 minutes.

"Our flight team is tracking opportunities for astronauts onboard the station to photograph both the eclipse and the Moon's shadow on the planet," says Daniel Huot (NASA Johnson Space Center) "They have solar filters for photographing the eclipse itself and will have one opportunity to see the Moon's shadow."

Astronauts have witnessed solar eclipses from space before, starting with the partial solar eclipse caught by Gemini 12 on November 12, 1966. More recently, NASA astronaut (and amateur astronomer) Don Pettit captured a total solar eclipse over the Pacific in May 2012, and European Space Agency astronaut Samantha Chistoforetti nabbed the partial phase of the March 20, 2015, total solar eclipse over the Faroe Islands. NASA astronaut Randy Bresnik recently arrived aboard the ISS and is, like Pettit, also a skilled photographer who is up to the challenge.

Thus far, though, no one on the ISS has managed to “thread the needle,” with a view passing through the narrow umbra of a total solar eclipse. Such a view would, of course, be fleeting, as the ISS moves 17,000 mph from southwest to the northeast, while the umbra of the Moon crosses the U.S. on August 21st from the northwest to the southeast at speeds up to 1,400 mph near mid-eclipse.

ISS vs the eclipse
The first pass of the ISS during the eclipse at 16:41 UT (note: the inset shows the eclipsed Sun; the graphics are from the Sun's perspective.

NASA currently plans on three opportunities to spy the eclipse during partial phases. The first pass will occur at 16:41 Universal Time (UT), just prior to the touchdown of the umbra over the Pacific at 16:49 UT, with partial phases of the eclipse already underway for western North America. ISS astronauts will see a 37% eclipsed Sun on this first pass.

The second pass of the ISS during the eclipse at 18:24 UT.

On pass two at 18:24 UT, things could get interesting. Although the ISS will not pass through the umbra, it should be visible from the station as it races races across Illinois, Kentucky, and Tennessee near maximum totality. Mir cosmonauts managed to catch this kind of view during the total solar eclipse crossing Europe one saros cycle ago, on August 11, 1999.

The third pass of the ISS during the eclipse at 18:16 UT.

Finally, the ISS crew will say goodbye to the eclipse as it departs Earth over the mid-Atlantic. This could provide an amazing opportunity to catch the “horns” of the eclipsed Sun setting behind the limb of the Earth, as the Sun fattens from 85% coverage to 27%.

At present, these times are approximate. The ISS is scheduled to perform an orbital boost on August 9th, and there's always the possibly of an unscheduled Debris Avoidance Maneuver (DAM) over the next few weeks.

“Flight controllers are still finalizing the details and identifying windows that might give a view of the Sun during the eclipse,” says Huot. ISS crew will be shooting the Sun out the cupola window using DSLRs and filter-covered lenses.

Catching a Transit of the ISS on Eclipse Day

GOES eclipse
GOES-10 sees the shadow of the Moon cross the Earth on February 26, 1998.

As the ISS passes overhead, there's also a good chance to nab the station transiting the partially eclipsed Sun during those first two passes. Renowned astrophotographer Thierry Legault captured the ISS crossing a partially eclipsed Sun from Oman on January 4, 2011.

This kind of shot takes some planning, as you have to be right along the precise path of the transit at the right time. You'll need the ability to shoot at a high frame rate or video with a properly filtered camera rig equipped with a zoom of at least 400 mm or better, to produce a good-sized disk of the Sun. ISS transits of the Sun or Moon are quick, often lasting less than 1 second. I like to have an accurate audible time hack via WWV Radio on shortwave AM playing in the background as well to know when to begin shooting.

CalSky is your best bet for precise transit predictions leading up to the eclipse. Keep in mind, the orbit of the ISS changes over time due to periodic boosts and atmospheric drag, so check those pass predictions within 48 hours of eclipse day.

Other missions may see the eclipse from space as well. The joint JAXA/NASA mission Hinode observes the Sun from a low-altitude orbit, as does the European Space Agency's Proba 2. Full-disk Earth-observing satellites such as DSCOVR, Himawari 8 and GOES 15 also typically nab the umbra of the Moon sliding across the face of Earth as well.

Another big question is the exact shape of the corona — the pearly-white aura of plasma surrounding the Sun seen only during totality — on eclipse day. We're inside the one Carrington solar rotation (that is, one rotation for 26#176; solar latitude, a period of 27.3 Earth days), and the National Solar Observatory Integrated Synoptic Program recently released a prediction for what shape the corona should take come eclipse day:

NASA will also employ a pair of converted WB-57 bombers to chase totality's shadow. In addition to observing the solar corona, the aircraft will take infrared images of Mercury pre- and post-totality, as well as sweep the skies near the eclipsed Sun for tiny Vulcanoid asteroids.

The big advantage to taking to the air and space, of course, is not having to worry about eclipse-day weather. We should start seeing the first long-range forecasts for those of us on the ground late next week, and we'll be watching Clear Sky Charts, Skippy Sky and NOAA models the weekend prior.

Remember, you don't need clear skies, just a clear view of the Sun during those precious minutes of totality!



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