Continue reading

24-03-09 Moon shadows signal approach of Saturn equinox

For the first time,Cassini has captured the shadows of the planet’s moons on Saturn’s broad expanse of rings as the majestic planet approaches equinox.Just like the Earth,Saturn’s spin axis is tilted relative to its motion around the Sun.This means that from the view point of Saturn,the Sun makes a cyclical passage across the Saturnian sky,sweeping from the southern hemisphere to the north and back again.One full cycle of Saturn’s season is equivalent to 29.5 Earth years,meaning that the Sun passes through the plane containing the planet’s rings roughly every 15 Earth years.During this celestial alignment,the shadows of the planet’s rings fall in the equatorial region on the planet,and the shadows of Saturn’s moons external to the rings,especially those whose orbits are inclined with respect to the equator,begin to intersect the planet’s rings.Any vertical protuberances within the rings,including small embedded moons and narrow vertical warps in the rings will also cast shadows on the rings.At exactly the moment of equinox,the shadows of the rings on the planet will be confined to a thin line around Saturn’s equator and the rings themselves will go dark,being illuminated only on their edge