Eclipses 'on demand' mark a new era in solar physics

Human beings have long lived in awe of the vast and starry skies — particularly during a solar eclipse, wherein the very laws of nature feel inverted. Before modern astronomy, solar eclipses were often assigned mythological or theological significance, which likely contributed to our enduring fascination with them.

That fascination took a seismic step forward this month, with the European Space Agency's launch of its Proba-3 mission. The groundbreaking project will enable researchers to create artificial solar eclipses for study on demand. Comprised of twin satellites Occulter and Coronagraph, Proba-3 will see the pair working in tandem to create a "precisely-controlled shadow from one platform to the other," the ESA said, opening "sustained views of the sun's faint surrounding corona."

Here's what makes the Proba-3 mission so unique, and what researchers hope to get out of it now that the project is off the ground.

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'Accuracy down to the thickness of the average fingernail'

The Proba-3's twin satellites, both of which were launched together from India's Satish Dhawan Space Center earlier this month, are each "about the size of a washing machine," The Washington Post said. Once in position, Occulter will "line itself up with the sun and use a disc — the stand-in for the moon — to cast a shadow onto the Cornograph," which can then be analyzed and studied like a natural eclipse. That may seem like a fairly straightforward proposition, but what makes the Proba-3 mission so special is the astonishing degree of precision involved: To be considered successful, the mission's satellites must "achieve positioning accuracy down to the thickness of the average fingernail while positioned one and a half football pitches apart," said Proba-3 mission manager Damien Galano. And all of this while speeding around the Earth.

If everything goes to plan, the receiving Coronagraph satellite will then be able to record data on the sun's corona, its "wispy, unfathomably hot outer atmosphere, which is usually lost in our star's glare," Space.com said. (The Week and Space.com are both owned by Future plc.) Once operational, the satellites will circle the Earth every 19 hours on a "lopsided" elliptical orbit, The Associated Press said. Twice a week, six of those hours "at the farther end of certain orbits" will be spent creating and studying artificial eclipses, while other loops will be focused on "formation flying experiments."

Solar mysteries and formation flying futures

Scientists hope that by artificially generating eclipses, they can study the "counterintuitive" temperature of the sun's corona, which is approximately 200 times hotter than the star's actual surface, Gizmodo said. The corona also "drives solar wind and coronal mass ejections," which can affect certain technologies both in orbit around, and on, Earth. But ultimately, it is Proba-3's extraordinary precision in orbit that "may end up being the mission's most lasting legacy," Space.com said.

Lessons from the project could someday "be extended to larger pairs of satellites," which would then be able to "block out starlight and allow scientists to go planet hunting," the Post said. "Imagine multiple small platforms working together as one to form far-seeing virtual telescopes or arrays," said the ESA. Proba-3 scientists expect the project will begin pushing out its eclipse observations "in about four months."