Saturn will be at opposition on 24 February 2008 and so will be well placed for observation over the next few months. It will be in the constellation of Leo, lying to the east of Regulus. The planet’s apparent retrograde motion will carry it towards Regulus and the two objects will be a fine sight both with the naked eye and with binoculars. They will start to separate again in early May.

At opposition, the south pole of the planet and hence the south face of the rings will be tilted towards the Earth by approximately 8 degrees. This narrow tilt will make the rings more difficult to detect in the very smallest of telescopes, but they will still be readily visible in telescopes of approximately 7 cm aperture.

(Figure 1. General view of Saturn. Image taken by David Arditti 12 December 2007 with a C14 Schmidt Cassegrain.)

The reduced tilt also means that more of the northern hemisphere is now on view compared to the last apparition. Both of the major belts (the North and South Equatorial Belts) are visible even in small telescopes.

Two light spots were reported during December 2007 and January 2008. One was in the in the South Tropical Zone and the other was in the zone between the components of the South Equatorial Belt (the SEBZ). More observations are required to confirm if these spots still exist and to track their motions.

Small telescopes will show the satellite Titan. Slightly larger telescopes of  7 to 10 cm aperture will allow Rhea and Iapetus (at its brightest) to be seen under reasonable conditions. Iapetus varies in magnitude as it moves around its orbit and is at its brightest when at western elongation. A larger telescope will be required to see it when it is at its faintest. Telescopes of 10 to 15 cm aperture should allow Dione and Tethys to be observed, especially when they are near their respective elongations. Larger instruments or the use of digital imaging techniques may allow the satellites Mimas, Enceladus and Hyperion to be recorded. Predictions of the positions of all of these satellites relative to Saturn are given in the BAA Handbook.

The orbits of the inner satellites lie very close to the plane of the rings. The reduced ring tilt now means that the orbits of the satellites from Tethys inwards appear to cross in front or behind the planet as seen from the Earth. Consequently transits of these satellites across Saturn’s disk will occur when they are at the appropriate positions in their respective orbits. Transits of even the largest of these inner satellites, Tethys, will be very difficult to observe with amateur equipment. However David Tyler has already managed to image a transit of Tethys and its shadow using a C11 Schmidt-Cassegrain telescope. Over the coming months it will be interesting to establish what is the minimum size of telescope that is required to observe the Tethys transits.

Transits of Dione also occurred early during the apparition but these ceased from approximately mid February due to a slight increase in the apparent tilt of its orbit as seen from the Earth. Transits will recommence again in July but by this time Saturn will be moving towards solar conjunction.

Mike Foulkes. Saturn section director.

(Figure 2. Transit of Tethys. Red light image taken by David Tyler on 10 December 2007 using a C11 Schmidt Cassegrain in Barbados. )