Article Posted on : - Sep 06, 2009

Saturn's rings backlit by the Sun. Image Credit: NASA

NEW DELHI (PTI): Saturn will be seen without rings from Monday. They have just become invisible to us due to a rare celestial phenomenon.

Explaining the phenomenon, which occurs after every 14.7 years, R C Kapoor, a scientist at the Indian Institute of Astrophysics, said, "Saturn is going through a phase called 'Ring Crossing'. In this condition, its rings become aligned along our line of sight and are therefore very difficult to see."

The Saturn's rings keep tilting in different directions as viewed from the Earth, due to changing geometry, as it moves around the Sun. At times, when the geometry is very favourable, the rings appear face on, spread out and clearly visible. This had happened in 2000, he said.

"In the present situation, the rings of the planet are tilted edge-on to Earth, making them impossible to see," C B Devgun, President of Science Popularisation Association of Communicators and Educators (SPACE), said.

Devgun said, since the ring system is extremely thin, the entire system becomes invisible during this phase (ring crossing) of around 15 days.

The complete edge-on phenomenon was visible on September 4, he informs.

Since then, the view of Saturn's rings has been slowly tilting towards us in such a way that they are now visible almost edge-on, he added.

Something like this was first noticed around 400 years ago when Italian astronomer Galileo Galilei first turned his telescope towards Saturn, Devgun said.

One can see the no-ring Saturn with the help of a telescope of about five cm aperture or more and a magnification upward of 100 for a good view.

Of the four planets with rings -- Saturn, Jupiter, Uranus and Neptune -- in the solar system, Saturn has the most prominent ring system.

The planet takes about twenty nine-and-a-half years to revolve around the Sun. While it does so, its axis of rotation and the plane of the rings are tilted 26.7 degrees to the plane of its orbit.

The angle and direction of tilt are fixed in space. Thus, as Saturn moves in its orbit, one can alternately see the north and south sides of the rings for almost 15 years each.

In between, the rings appear edge-on to the line of sight and seem to disappear.

For the past 15 years, south side of the rings were visible. On September 4, the rings were positioned edge-on which made the planet appear without any ring.

On September 17, when it will be on the other side of the Sun from the Earth, the north side of the ring system of the planet would come into visibility and will be visible until 2025.