During the maneuver, the solar-powered, windmill-shaped Juno will briefly pass into Earth's shadow and emerge over India's east coast. At closest approach, Juno will fly within 350 miles of the Earth's surface, passing over the ocean off the coast of South Africa shortly before 12:30 p.m.
The rendezvous was designed to bump Juno's speed from 78,000 mph relative to the sun to 87,000 mph enough power to cruise beyond the asteroid belt toward its destination.
During the gravity assist, the spacecraft's JunoCam, a wide-angle color camera, will snap pictures of the Earth and moon. Weather permitting, skywatchers in India and South Africa with binoculars or a small telescope may see Juno streak across the sky. Ham radio operators around the globe were encouraged to say "Hi" in Morse code a message that may be detected by Juno's radio.
By space mission standards, Juno's flyby was expected to be low-key compared with the Curiosity rover's nail-biting landing on Mars last year.
"Our expectation is we will come through nice and clean," said project manager Rick Nybakken of the NASA Jet Propulsion Laboratory, which manages the $1.1 billion mission.
Despite a government shutdown that has prevented NASA from updating its website or tweeting, the space agency's missions continue to operate. Earlier this week, NASA's newest spacecraft, LADEE, slipped into orbit around the moon.
Since the 1970s, spacecraft have visited or flown past Jupiter including the Voyagers, Pioneers, Galileo, Ulysses, Cassini and, most recently, the Pluto-bound New Horizons. Juno promises to venture closer than previous spacecraft, circling the planet for at least a year to study its cloud-covered atmosphere and mysterious interior to better understand how the giant planet formed.
Juno was scheduled to arrive at Jupiter on July 4, 2016 after journeying 1.7 billion miles. Chief scientist, Scott Bolton of the Southwest Research Institute, said he's pleased with Juno's performance so far.
"The mission is going great and after this flyby of Earth, our next stop is Jupiter," he said.