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NASA is asking Earthlings to participate in the first-ever interplanetary photo bomb.

At 3:27 p.m. on Friday, the Cassini spacecraft will be in a unique position to photograph Saturn, and for 15 minutes, it will be able to capture Earth from deep within the solar system for the third time ever.

"Earth will appear as a tiny blue speck just outside of E ring on Saturn," said Paulmichael Maxfield, gallery programs coordinator at the Natural History Museum of Utah.

The museum and the University of Utah's Department of Physics and Astronomy will host activities from 2 to 4 p.m., including setting up special telescopes where viewers can see the sun and possibly Saturn during the daytime. U. scientists Benjamin Bromley, who specializes in the rings and moons of Saturn, and Tabitha Buehler, who specializes in new stars, will be on hand to answer questions.

"It's a great time to visit the museum to talk with local experts and participate in hands-on activities," Maxfield said.

For the Saturn photo, staff will provide fun costumes and signs.

Downtown, folks who signed up previously will pose for the Saturn photo on the rooftop garden of the Salt Lake City Main Library for a BBC documentary called "Human Universe," which will look at humans' continual search for their place in the cosmos.

But Patrick Wiggins, NASA/JPL solar system ambassador to Utah, reminds everyone they don't need a formal gathering to say hi to the sixth planet.

Simply grab your colleagues or kids, walk outside, look low on the southeast horizon and remember to smile.

"We don't want Saturnians thinking we're a bunch of unhappy people," he joked.

North America will be illuminated at the time of the photo, though of course no one will be identifiable from hundreds of millions of miles away. It will take the light from Earth 1 hour and 20 minutes to travel to Cassini's cameras, Wiggins said.

"But maybe a couple of photons from your area made it into the photo," he said.

The conditions to actually aim a camera back at Earth from such a distance are rare as the sun's bright rays fry delicate camera equipment. On Friday, Cassini's orbit will take it to the far-side of Saturn from the sun. The planet will block those harsh rays, allowing the spacecraft's cameras to safely capture images of a backlit Saturn's atmosphere and rings and our tiny, blue dot of a planet.

While Wiggins is always excited about people getting excited about space exploration, he's even more excited to find out what the photographs of Saturn turn up this time. In 2006, Cassini photographed Saturn and its rings, giving researchers new details about Saturn's dusty, icy E ring and capturing Earth from the distance of 926 million miles away. (The first time Earth was photographed from deep inside our solar system was 23 years ago by Voyager I from 4 billion miles away.)

"You never know what you're going to find when they backlight the rings," Wiggins said. "The structures and systems of the rings are fascinating, with shepherding moons and the gravitational interactions. You just never know what they'll discover."

smcfarland@sltrib.com

Twitter: @sheena5427

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