Feature | August 17, 2017

Spectacular Eclipses in the Saturn System

by Bill Dunford

With a solar eclipse approaching on Aug. 21, 2017, which will be visible all across North America, you may have wondered: Do eclipses happen on other planets?

They certainly do in the Saturn system—with spectacular results.

On Earth, we see a solar eclipse when the Moon passes between the Sun and Earth, casting the Moon’s shadow on the surface of Earth. 

The Moon’s shadow falls on Earth, as seen by an astronaut aboard the International Space Station. Those on the ground within the shadow would see the Sun being blocked by the Moon--a solar eclipse. Credit: NASA.

Saturn has dozens of moons, not to mention the rings. Within this bustling “mini-solar system,” eclipses happen relatively frequently during certain seasons, and the Cassini spacecraft has captured some of these moments with its cameras. In addition, from its vantage point in space Cassini sometimes witnesses occultations of the Sun, when Saturn blocks out the light of the Sun as seen from the spacecraft. Cassini also images moons and rings at high phase angles, which means the subject is backlit by the Sun, with the Sun just out of the frame. These situations can lead to even more spectacular sights.

Here are a few scenes involving eclipses, occultations and high phase angles that Cassini has witnessed during its 13 years exploring the Saturn system.

Saturn
This is what it looks like when Saturn occults the Sun. The Sun is behind the planet in this view, setting the rings and its atmosphere aglow. Cassini acquired the images for this mosaic as the spacecraft drifted in the darkness of Saturn's shadow for about 12 hours on Sept. 15, 2006, allowing a multitude of unique observations of the microscopic particles that compose Saturn's faint rings. A remarkable bonus: click to enlarge the image, and look on the left side just outside and above the bright main rings. Earth can be seen as a blue dot floating in space. Credit: NASA/JPL/Space Science Institute.
Backlit
Cassini took this image of Saturn’s intriguing moon Enceladus while the Sun was nearly behind the moon. This provided dramatic backlighting for the jets of icy material that continually erupt from Enceladus’ sub-surface ocean. The illumination on the right side of the moon is actually “Saturnshine”—sunlight reflected from the surface of the planet. Credit: NASA/JPL/Space Science Institute.
Titan
This high-phase-angle shot shows sunlight illuminating the halo formed by the thick, hazy atmosphere of Saturn’s giant moon, Titan. Enceladus can be seen at the lower right, and the backlit rings slice through the middle of the image. Credit: NASA/JPL/Space Science Institute.
Titan
Saturn’s moon Titan casts a shadow on the planet’s cloud tops. An observer located within the darkened circle would see a solar eclipse. The rings, seen nearly edge-on, are at Saturn’s equator. Credit: NASA/JPL/Space Science Institute.
Saturn rings
During certain seasons, some Saturnian moons have a solar eclipse every day when their orbit takes them into the planet’s shadow. Here, the tiny moon Prometheus is seen emerging from the darkness. Credit: NASA/JPL/Space Science Institute.
Mimas
The shadow of Saturn's moon Mimas falls across the rings and straddles the Cassini Division in this natural color image. If you were among the ring particles there, you’d see many spectacular sights, one of which would be Mimas eclipsing the Sun. Credit: NASA/JPL/Space Science Institute.
Saturn clouds
The rings themselves cast dramatic shadows on Saturn’s cloud tops. If you were among these shadows, the sunlight would be dimmed, but the Sun would not disappear entirely; the rings are so thin they are translucent. Credit: NASA/JPL/Space Science Institute.