SOHO watches Saturn and Cassini pass behind Sun

In this SOHO image, taken 21 July 2005, the Sun is represented by the white circle in the centre. Saturn is the bright object to the left of the Sun.

Saturn was approaching a position called ’superior conjunction’, that is, it would be almost directly behind the Sun as seen from Earth. Therefore the NASA/ESA/ASI Cassini spacecraft, in orbit around Saturn, was not able to send or receive transmissions normally.

As Cassini passed close by the limb (edge) of the Sun on 24 July, communications became impossible because of the Sun’s radio noise. The spacecraft regained full communication with Earth on 27 July, once again returning Saturn science data.

In the meantime, Cassini radio scientists are taking advantage of this opportunity to study the Sun’s corona from its effects on the radio signals that reach Earth. This is a joint co-ordinated observation involving two SOHO instruments (UVCS and LASCO), plus Cassini and some ground-based radio sites.

Interestingly, the bright ’streak’ accompanying Saturn is not the rings but a result of ’pixel bleeding’.

SOHO, the ESA/NASA Solar and Heliospheric Observatory, orbits the Sun parked in one of the five gravitationally neutral spots, called ’Lagrange points’. This specific spot, called L1, stays in the same place relative to the Sun and Earth, offering SOHO a continuously uninterrupted view of the Sun.