What NASA Can Learn From the March 9 Eclipse

Next week's total solar eclipse will give NASA a rare peak at the Sun's atmosphere.

On Wednesday, March 9, those lucky enough to find themselves within a few hundred miles of Indonesia will be treated to a total solar eclipse, a relatively rare space event in which the moon completely blocks out the sun during its transit.

Beautiful in their own right, total solar eclipses also provide a great opportunity to study the Sun in ways that are only possible when the moon is in the way. Although the Sun will be almost totally obscured by the moon, the Sun's atmosphere, or corona, will still be visible as a ring around the moon, and this is what's got space scientists at NASA all fired up about next week's eclipse.

The Sun's corona extends millions of miles into space, although it is the inner corona that is of particular interest to astronomers since it is believed to hold the keys to all sorts of solar mysteries, such as the acceleration of solar wind, the generation of coronal mass ejections (explosive clouds of plasma), and the heating of the corona as a whole (which is hundreds of times hotter than the surface of the Sun).

"The sun's atmosphere is where the interesting physics is," Nelson Reginald, one the space scientists from NASA's Goddard Space Flight Center who will be in Indonesia for the eclipse, said in a press release. "A total solar eclipse gives us the opportunity to see very close to the solar limb."

The corona is technically always visible, but it is about a million times less bright than the Sun's face (or about as bright of the moon) so it's usually lost in the light. To study the corona when there's no eclipse, space scientists usually make use of a coronagraph, which creates artificial eclipses by using an opaque disk to block the Sun's face. While this works great for studying the outer corona, the coronagraphs are unable to reveal the inner corona. This is because light bends around sharp edges—a phenomenon known as diffraction—so in order to combat this effect, coronagraph disks obscure the inner corona as well as the Sun's face.

That means that the only time to study the inner corona is for a precious few minutes approximately every 18 to 24 months during a total solar eclipse. And this time around, NASA doesn't intend to waste a second.

During next week's solar eclipse, NASA will use the three minutes of totality to study polarized light coming from the inner corona, which contains valuable information about the temperature and velocity of electrons in that region.

The instrument that NASA will be using to study the movement of electrons in the Sun's inner corona was first put to use in 1999 during the eclipse in Turkey. Previously, the instrument's operators would use a hand-turned polarization wheel to take three images in each polarized direction (light is polarized when it oscillates along a single plane). When you only have a few minutes for observation, such a slow process severely limits the amount of data that can be generated from the eclipse, so the NASA team spent the last year rebuilding the machine.

The new camera has thousands of small polarization filters, each of which can read light polarized in four different directions simultaneously. This eliminates the need the change the polarization filters between each exposure, allowing scientists to study more wavelengths during their precious three minutes.

"We've cut down the length of time required for our experiment by more than 50 percent," Nat Gopalswamy, principal investigator of the eclipse experiment at Goddard, said in a statement. "The polarization camera is faster and less risky, because it's one less moving part."

The new camera has already had a successful test run using the moon as a stand in and will go live on Wednesday from the Indonesian province of North Maluku.

If you won't be in Indonesia or the East Pacific for the main event, you can still follow along here, where NASA will be livestreaming the eclipse on March 8 from 8-9pm ET.