On Wednesday, two NASA aviators will tuck into their lunch, climb into a research plane, and take off from Keflavik airport on a western tip of Iceland. They'll head north towards Greenland, then bank south on a gently curving course 40 miles (64km) off the Icelandic coast. Their mission: chase an eclipse. Or rather, the eclipse will chase them - at more than 2,000mph (3,200km/h) across the ocean below.
At 50,000ft (15,000 metres), the moon's shadow will race up from behind, and the pilot aims to hit the point of greatest eclipse just as the shadow catches up. For anyone standing directly beneath - or treading water, given the geography - the world goes dark for 2 minutes 18 seconds. But by flying at 460mph along the eclipse path, the pilot stretches totality to nearly 3 minutes. More time to stare at the blotted-out sun, because why not extend the cosmic drama?
Cary Klemm, a sensor equipment operator at NASA's Johnson Space Center in Houston, who has flown eclipse missions, described the high-altitude experience: "The big difference is that in the cockpit of an aircraft at 50,000 feet, it's very bright in the sun. There are no clouds above you, and then all of a sudden, you're hit with this slam of shadow." He added, "You feel the temperature drop off; you'll notice that you need more light from your instruments, and it's kind of a weird, eerie shadow that you're surrounded by. It wraps around the view in the cockpit."
Hidden in the nose cone of the WB-57 aircraft are four cameras. These will take dozens of pictures a second of the occluded sun in different wavelengths. The images should capture large, looping ribbons of plasma called prominences and magnetic explosions called nanoflares. Only with the sun's disc blocked out are such observations possible.
"I'm super-excited," said Dr Amir Caspi, principal investigator on the mission at Southwest Research Institute in Boulder, Colorado. "Solar eclipses give us an opportunity to do science we couldn't do at any other time."
Despite the name, nanoflares pack a punch, each releasing thousands of atomic bombs' worth of energy. They at least partly explain why the corona, the sun's outer atmosphere, is so hot - more than 1,000,000°C - while the surface is a mere 6,000°C. Aircraft are hard to beat for these observations. Ground-based cameras have clouds and atmospheric interference; space-based cameras are above such concerns but can send back only so much data. "As you can imagine, this is terabytes of information," Caspi said.
The WB-57 is based on the English Electric Canberra bomber, the RAF's cold war tactical nuclear strike aircraft, and flies above the clouds in the stratosphere. Other planes have been used for eclipse missions. In 1923, the US navy sent a fleet of biplanes to observe an eclipse, without much success. Fifty years later, scientists persuaded the French to cut holes in the roof of a Concorde prototype; hurtling over the Sahara at Mach 2, they kept up with an eclipse shadow for 74 minutes.
The more scientists learn about the sun, the better they should grasp space weather - the barrage of energetic particles and radiation hazardous to astronauts, satellites, and even power grids and communications on Earth. Caspi said: "Understanding space weather is critical for us as a technological species, and it starts with understanding the processes at the sun."
Eclipses are not all about science though. "What percentage of humanity has ever witnessed a total solar eclipse? It's a fraction of a fraction of a per cent," Caspi said. "If you're part of that rare group, you're connected to the Earth and the sun and the solar system. It's mind-blowing. It makes you feel very special, but also very small because you are this little mote in the universe."