News from May 24, 2017
Over 13 years in which the Cassini spacecraft has been investigating the Saturnian system it could observe how the appearance of the ring planet changed continuously. Because of its inclined rotation axis, Saturn has seasons just like Earth. During the almost 30 years in which Saturn orbits the sun, both hemispheres are illuminated more or less by the sun. When Cassini arrived at Saturn in 2004, it was northern hemisphere winter and only little sunlight illuminated the northern hemisphere. The north pole was in complete darkness then and the ring system was illuminated only from below, such that it caused long shadows in the northern latitudes.
On 11 August 2009 Cassini was able to observe the spectacle of equinox where both hemispheres of the planet are illuminated equally and the sunlight strikes the edge of the rings at right angle. At this rare constellation the rings appear very dark and the shadow of the ring system is only a narrow band pointing exactly at the equator of the planet. After this event spring began in the northern hemisphere and the sunlight climbed to higher latitudes.
About 7.5 years later at maximum solar altitude the complete northern hemisphere including the polar region is illuminated by sunlight. Moreover, the top side of the ring system is lighted. With equinox at 24 May 2017 summer begins in the northern hemisphere of Saturn, and winter in the southern latitudes. Hence, until the end of the mission in September 2017 Cassini can observe further seasonal changes on the surface of Saturn.
NASA/JPL-Caltech/Space Science Institute