July 19 will be a good day to go outside and wave at the sky. You may get some strange looks from your neighbors, but you would be joining scores of other astronomy enthusiasts around North America doing the same. On July 19, NASA’s Cassini spacecraft, which is currently studying the planet Saturn, will turn around and photograph Earth through Saturn’s rings. The final image will show enormous planet Saturn and its rings in the foreground, with Earth as a pale blue dot on the fringe of the rings in the background. During the photo, North America will be in daylight, so NASA is encouraging people in North America to hold “Wave at Saturn” parties to celebrate the event. NASA also will be accepting photos submitted by citizens of themselves waving at Saturn to be merged into a collage commemorating the event.
Cassini’s photo is scheduled to begin at 4:27 p.m. on July 19 and will end after about 15 minutes. (The photo will take 15 minutes because Saturn is so large that many photos will be taken and stitched together into the final image.) At that time, Saturn will be in the southeastern sky, and Cassini will be about 900 million miles from Earth.
Earth will be much too far away for you to actually show up in the photo, rather the excitement revolves around the idea of and symbolism of what is occurring. Other such photos have been taken from Saturn in 2006 and 2012, but this will be the first real color photo taken from Saturn and the first time the public will have advance notice of such a photo opportunity.The photo will be posted on NASA’s website after it has been beamed back to Earth and processed.
(Oh, and in case you were wondering or are a stickler about detail, it will take the light from Earth about 80 minutes to reach Cassini, so the image of Earth recorded in the 4:27 p.m. photograph will be of Earth at around 3:07 p.m.)
The night sky this month contains few planets. Saturn dominates the night sky and is a good target for telescopes or binoculars. Saturn appears almost directly southeast at sunset this month just under halfway up the sky. Saturn looks like a pale yellow star, and looks very similar to the yellow star named Arcturus above it.
Look high in the east after sunset to see one of the most conspicuous star collections of the summer, the “Summer Triangle”. It is composed of three bright stars from three different constellations. The brightest and furthest west is a star named Vega; the furthest south star is named Altair, and the furthest north star is named Deneb. Deneb is the bright star in the constellation Cygnus, the swan. Cygnus is also commonly known as the “Northern Cross.” Once you’ve located Deneb, face east to see the cross. It will be laying on its side, the bottom of the cross pointing south and the arms pointing east and west. Using a bit of imagination, you should be able to imagine a swan flying south, the star Deneb forming its tail.