Fotografia - Lisboa noctura - Praça dos Restauradores

Estúdio Mário Novais, Praça dos Restauradores, Lisboa, sem data Colecções daFundação Calouste Gulbenkian, Lisboa, Portugal (Flickr Commons)

Astronomy picture of the day - 2017 February 22 - Daphnis and the Rings of Saturn

Daphnis and the Rings of Saturn 
Image Credit: NASA, JPL-Caltech, Space Science Institute, Cassini

Explanation: What's happening to the rings of Saturn? Nothing much, just a little moon making waves. The moon is 8-kilometer Daphnis and it is making waves in the Keeler Gap of Saturn's rings using just its gravity -- as it bobs up and down, in and out. The featured image is a wide-field version of a previously released image taken last month by the robotic Cassini spacecraft during one of its new Grand Finale orbits. Daphnis can be seen on the far right, sporting ridges likely accumulated from ring particles. Daphnis was discovered in Cassini images in 2005 and raised mounds of ring particles so high in 2009 -- during Saturn's equinox when the ring plane pointed directly at the Sun -- that they cast notable shadows.