The upcoming solar eclipse is a pretty big deal for science.
The moon's shadow will soon completely block the sun over parts of Southeast Asia for a few brief minutes, giving sky watchers a rare and beautiful sight, and astronomers an uncommon chance to study some important features of the sun.
Solar eclipses occur in one form or another at least twice a year (they can occur as many as five times, though that is incredibly rare). But some eclipses are more useful to scientists than others, and many of them are difficult to observe. The one scheduled to be visible over parts of Southeast Asia and the Western Pacific on Tuesday night, Eastern time, (Wednesday morning, by clocks in Indonesia) will be a special kind of eclipse over a populated area — a somewhat rare combination, according to a NASA scientist who spoke with CNBC.
First, the coming eclipse is a total solar eclipse — one of two types of solar eclipses. The other kind, annular eclipses, are slightly different.
The moon's orbit around the earth is oval shaped, not perfectly round, and its distance from Earth varies. During annular eclipses, the moon is too far from Earth (and too close to the sun) to completely block the vastly larger sun from view. The edges of the sun shine along the moon's perimeter in a thin gold ring.
A total eclipse, as the name suggests, more completely blocks our view of the sun, leaving only a tiny reddish band of light visible around the edges, called the limb, and whitish wisps radiating outward, called the corona.
Both are incredible sights to behold, but only total eclipses are dark enough to allow scientists to view the corona — the wispy, ghost-like outer atmosphere around the sun, according to Alex Young, associate director for science in the heliophysics science division at NASA's Goddard Space Flight Center.
"We do have some instruments called coronagraphs on the ground and in space that create an artificial eclipse, but they are not as good as nature," Young told CNBC. "We don't get as close down to the surface of the sun as nature does."
Total solar eclipses show us the areas around the sun where all the action happens, Young said. This area is where the sun produces "solar weather" phenomena, like solar flares or coronal mass ejections, and the region is also where solar winds — material constantly blowing off the surface of the sun — are accelerated.
Apart from being fascinating for their own sake, these phenomena are important to understand because they have an impact on the rest of the solar system, including Earth.
Solar weather and eruptions can also affect satellites, and can create hazardous radiation for astronauts in space.
"That is why it is so important to understand why these things happen," Young said, "and perhaps someday to predict them, just as we predict weather here on Earth."
This eclipse will also let scientists test equipment and instruments on the ground that they may someday want to fly into space, Young said. Some NASA and U.S.-based researchers will test some telescopes and equipment that they hope to deploy for the next total solar eclipse in 2017, which will be visible in the United States.
"So you have all these things that are happening that will make this an exciting event for scientists and citizen scientists who are helping out," he said.
This eclipse will be especially visible from Indonesia, spurring excited would-be watchers to flock to that country for the event.
People elsewhere in the world won't be able to see much — or any — of the eclipse in the sky, but they can watch it online. Science museums, such as the Exploratorium in San Francisco, will be webcasting the eclipse.
One commercial flight — Alaska Airlines flight 870 — will even divert its flight path to give its passengers a view.
Young urged people who will not be able to directly witness this eclipse to try to see the next one in the U.S. in 2017.
"Everybody I have ever talked to has said this is sort of a life-changing experience, to see a total solar eclipse," Young said. "I really recommend that if anyone has the opportunity to do it, I encourage them to take it."