By Judith Burns
Science reporter, BBC News
At equinox, the rings turn edge-on to the Sun, reflecting almost no sunlight
Raw images of the moment Saturn reached its equinox have been beamed to Earth by the US Cassini spacecraft.
Scientists are studying the unprocessed pictures to uncover new discoveries in the gas giant's ring system.
Equinox is the moment when the Sun crosses a planet's equator, making day and night the same length.
During this time, the Sun's angle over Saturn is lowered, showing new objects and irregular structures as shadows on the otherwise flat plane of the rings.
Saturn's orbit is so vast that Equinox happens only once every 15 Earth years.
At the moment of equinox, the rings turn edge-on to the Sun and reflect almost no sunlight.
This is the first equinox since 1994 and the first time there has been an observer, in the shape of the joint US and European spacecraft, Cassini.
In an email, Dr Carolyn Porco, leader of Cassini's imaging team, said the long-awaited images did not disappoint: "Even a cursory examination of them reveals strange new phenomena we hadn't fully anticipated.
"Over the next week or two, the [Cassini] imaging team will be poring over these precious gems to see what other surprises await us, and, as usual, we will announce what we have found as soon as we can."
Cassini was launched in October 1997 from Florida's Cape Canaveral Air Force Station. It arrived at Saturn in July 2004 to embark on a four-year mission of exploration around the planet and its moons.
The spacecraft is still operating well and has been re-programmed to carry out new tasks. Its current mission is to answer some of the questions raised by its earlier observations.