ECLIPSES ON DEMAND

Inside an unassuming building, behind a damp car park in Antwerp, Belgium, scientists are teaching two spacecraft to be dance partners for a performance that will take place in front of the Sun.

- NOA LEACH

It's early April, just days before the Great American Eclipse, when the Moon will slip in between us and our star, giving excited astronomers a rare, but brief, chance to see its corona - the 'crown' that forms its outer atmosphere.

If the two spacecraft can be taught to perform their dance correctly, the scientists in Belgium will be able to create their own, artificial eclipses and observe the corona whenever they want. Why? Because doing so could help us solve one of the biggest mysteries in solar physics: what's happening inside the Sun's fainter coronal ring.

There's a lot we don't know about the corona - why it's over a million degrees hotter than the Sun's surface, for instance. Or why space.weather (the radiation, particles, magnetic fields and matter ejected by the Sun that can interact with Earth's atmosphere and disrupt our electrical systems) originates from it. We don't know because the Sun's light outshines the corona, making it impossible to see, unless something blocks the Sun's light. Something like the Moon during an eclipse... or a pair of spacecraft performing a carefully choreographed dance.

The spacecraft in question are of part the European Space Agency's (ESA's) Proba-3 mission and have to be taught to dance with each other because they'll be too far from Earth to control with the precision required to produce artificial eclipses. The mission's full name, Project for OnBoard Autonomy, gives a clue (albeit an unwieldy one) as to the level of involvement its controllers on Earth expect to have.