What a Solar Eclipse Looks Like (When You're Seeing It From Mars)

Curiosity uses its version of a pinhole projector to view -- and capture -- a Martian eclipse.

The Martian moon Phobos passes across the edge of the sun. The raw photo, captured by the Curiosity rover, has been enlarged to twice its original size. (NASA/JPL)

On Thursday, Mars's Gale Crater was treated to a fantastic sight: a partial solar eclipse. An eclipse very similar to the kind we're used to seeing from here on Earth, but with the sun blocked, in this case, by a different moon: Phobos, one of the two moons that orbit Mars.

Fortunately for us, Curiosity was there to take a picture of Phobos's transit. Fortunately for us, as well, Curiosity took precautions to protect its vision as the transit took place. (As NBC's Alan Boyle put it: "You wouldn't want Curiosity to blow out its camera on Mars.") So, to capture the image above, the rover's Mastcam used a neutral density filter that protected Curiosity's imaging system in the same way that a pinhole projector protects human eyes during an eclipse. In Curiosity's case, the filter reduced the Mars-seen sunlight to a thousandth of its natural intensity.

The image above, it's also worth noting, isn't as rare as it would be as observed from Earth. Phobos orbits Mars at a distance of only 3,700 miles, making it closer to its host planet than any other known planetary moon. (Our moon, for comparison, orbits at a distance of over 200,000 miles.) Because of that, Phobos transiting the sun can be seen from some point on Mars pretty much every day. And it will be only a year before a transit can be seen again from the Gale Crater.

But the relative commonality of the Martian eclipse doesn't compromise its splendor. And Curiosity isn't the first rover to capture the view. Below, via Bad Astronomy, is amazing video sent back by Opportunity in November 2010: the sun, hazy in its distance, eclipsed by one of those meandering Martian moons.