This image taken by NASA’s Cassini spacecraft wide-angle camera on Jan. 16, 2015, shows the moment in 2015 when Saturn’s shadow just barely reached across it’s entire main ring system. The shadow will continue to shrink until the planet’s northern summer solstice, at which point it will once again start lengthening across the rings, reaching across them in 2019.
Like Earth, Saturn is tilted on its axis. And, just as on Earth, as the sun climbs higher in the sky, shadows get shorter. The projection of the planet’s shadow onto the rings shrinks and grows over the course of its 29-year-long orbit, as the angle of the sun changes with respect to Saturn’s equator.
The image was obtained at a distance of approximately 1.6 million miles (2.5 million kilometers) from Saturn.