More than 30 years ago, en route to the Moon in December 1972, the astronauts of Apollo 17 took an extraordinary photograph. They captured the entire Earth on one frame of film, showing it to be a lonely blue marble in empty black space, streaked by clouds and the occasional continent or smaller bit of land. We have become so used to the picture that we sometimes forget its startling message: that a world that holds life is something small and special in the vast range of space.
On May 29 of 2008, the EPOXI mission took a set of pictures from an even more distant perspective, showing our Earth and its companion, the Moon, passing directly between EPOXI's spacecraft and Earth. By coincidence, the Earth showed Africa as the Moon passed by, the same continent appearing in the famous Blue Marble photo from Apollo 17. These images of the Earth and Moon together are a part of EPOXI's scientific mission to explore the planets of other stars -- in this case, as part of an effort to learn more about what an Earth-like planet looks like from such a distance that no details can be discerned, which includes understanding the appearance of an Earth-like planet orbited by one or more Moon-like moons. By learning what the Earth looks like from a great distance, we can learn more about how to engineer instruments to investigate Earth-like planets from even greater distance.
Caption: As part of the EPOXI mission's objectives to characterize the Earth as a planet for comparison with planets around other stars, the spacecraft looked back at Earth collecting a series of images. In the left image the Earth-Moon system is seen with the Moon beginning its transit in front of Earth. It was taken on May 29, 2008 through three filters: blue, green and orange, centered at 450, 550 and 650 nm respectively, while the spacecraft was 0.33 AU (49,367,340 km and 30,675,43 miles) from Earth. The image on the right is a simulation showing the view of Earth from the spacecraft's perspective.
Technical Details: 29 May 2008 0640 UT
450 (blue), 550 (green) and 650 (orange) nm
Image was stretched to make the moon brighter and easier to see beside the brighter Earth.
Just for fun: What is the phase of the moon from the spacecraft's perspective? From the Earth's perspective? Need help? Take a look at this diagram showing the geometry.
Alt. Caption: We all know what Earth looks like up close, but what does it look like from a distance, as seen by the EPOXI spacecraft? What are the Earth's global properties? How will observations of Earth from space help the astrophysicists characterize Earth-like planets around other stars?
EPOCh scientists observed the Earth with these questions in mind and are currently analyzing the data. Here's their first look!