Today’s the day! NASA’s Juno* spacecraft, launched back on August 5, 2011 (I should know, I was there) will get a little help from its friends (that’s us!) as it passes by Earth to get a gravitational power-boost on its way to Jupiter.

The exact time of Juno’s closest approach is 3:21 p.m. EDT (12:21 PDT / 19:21 UTC).

But wait, you ask… why would Juno come back to Earth after 2 years to get to Jupiter? Isn’t that losing distance? It might seem that way, but in space travel it’s all about saving energy. Bill Nye (yes, the Science Guy) explains:

So when you’re dealing with rockets and fuel (and budgets) and bopping between orbits across vast distances, it helps to use gravity to your advantage. After all, it’s like free energy!

Juno will really be skimming closely by Earth too, coming within 350 miles just over South Africa before heading back out into space. Read more on Ken Kremer’s Universe Today article here.

This flyby will also provide an opportunity to calibrate Juno’s instruments, and perhaps even get some really cool images of Earth and the Moon via JunoCam.

“While we are primarily using Earth as a means to get us to Jupiter, the flight team is also going to check and calibrate Juno’s science instruments,” said Dr. Scott Bolton of Southwest Research Institute, Juno’s principal investigator. “As another bonus, Juno is approaching the Earth from deep space, from the sunlit side. Juno will take never-before-seen images of the Earth-Moon system, giving us a chance to see what we look like from Mars or Jupiter. We plan to release a movie of this unique perspective of the Earth-Moon system shortly after the flyby.”

Want to watch Juno’s pass? The Slooh community camera is holding a public event online where you can tune in and watch live. Visit the Slooh site here.

So whatever you’re doing today at 3:21 p.m. EDT, stop and wave hi to Juno. She won’t be ’round these parts again. Next stop Jupiter, July 4, 2016! Go Juno!
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*This is where I would usually post a link to the mission site, but since NASA is still on furlough due to the U.S. government shutdown all NASA.gov sites are still closed. You can read more about this flyby on the Southwest Research Institute’s press release here though, and visit the SWRI Juno mission site here.

See images from JunoCam as they arrive on the MSSS site here: http://www.msss.com/junocam_efb/efbimg.html

UPDATE Oct. 15, 2013: Here’s a couple of color images of Earth made from raw images acquired by Juno as it approached the day side of Earth on Oct. 9th, at 3:08 p.m. EDT:

As JunoCam is a push imager and the data was taken in horizontal bands down a long vertical frame (as it was moving very quickly towards us) there’s a bit of misalignment between the RGB channels… still, a very cool snapshot of our world taken from hundreds of miles out in space!