Friday, July 19, you are invited to go outside, face east at 3:27 MDT, look to the horizon and wave.

Starting at that time, the Cassini spacecraft, which is orbiting the planet Saturn, will take pictures of Earth for 15 minutes. Linda Spilker of NASA's Jet Propulsion Laboratory said in a news release, "This is the first time Earthlings know in advance their picture will be taken from a billion miles away."

Cassini has been orbiting the ringed planet for years, and took a similar photo in 2006. At that distance, Earth is a small blue dot, so you won't be visible in the picture, but it's the principal of the thing.

The photos will be in natural color and will capture Earth and Moon in the same frame. Also, Cassini will be taking the photo through Saturn's rings. It has a 15-minute schedule to take the pictures.

Cassini took a photo of Earth in 2006. And Voyager I took an Earth photo from beyond Neptune in 1990. Those are the only two photos (that we know of) of Earth from the outer Solar System.

The public can share pictures of their Friday afternoon postures on Twitter, using the hashtag #waveatsaturn.

Or you can upload a photo at www.flickr.com/groups/wave_at_saturn/. The Facebook page is http://bit.ly/waveatsaturn.

Even though it's daylight, Saturn is in the sky. Take our word for it...and wave!