MONTH
Saturn
Best time to see: 20 July, From 00:00 BST (23:00 UT) Altitude: 16°
Location: Sagittarius
Direction: South
Features: Rings, atmospheric belts, occasional storms, moons Recommended equipment: 150mm or larger
The planet Saturn reaches opposition on 20 July. Opposition is the term used to describe when a planet lies on the opposite side of the sky to the Sun. In this position we are at the closest to that planet and consequently it appears bigger and brighter than at other times.
The more distant a planet is from the Sun and therefore Earth, the smaller these effects become. For example, we’re going to see major changes in the appearance of Mars as we head through to its opposition on 13 October. Jupiter too will be at its brightest and largest through the eyepiece on 14 July, but the changes are less impressive than those which will appear for Mars. And the progression continues through to Saturn with its brightness and increase in apparent size being fractionally less impressive than that which occurs with Jupiter.
Having said this, Saturn still has a trick up its sleeve in the form of the Seeliger effect. As the planet approaches opposition, the myriad particles which make up its ring system line up so that from Earth the shadows they cast on particles further back are hidden from view. The net ▲ effect is a brightening of the rings. This effect can normally be seen a few days before opposition, reaching a peak brightness at opposition and then fading off in the days after.
Saturn and Jupiter reaching opposition within a week of each other occurs as a consequence of both appearing close in the sky. On 20 July Saturn appears 7.1° east of Jupiter. At opposition, Saturn’s brightness will be mag. +0.4. A full Moon
– the Moon at opposition – lies near to both planets on the evening of 5 July and into the following morning.