Skywatchers in Western Europe (including the UK) should look low in the south-southwest around the start of nautical dusk (~8:30pm BST in the heart of the British Isles) on Monday, 17 September to see this close conjunction between Saturn and a Moon just past first quarter phase in the constellation of Sagittarius. AN graphic by Ade Ashford.Observers in the UK with a clear sky in the south-southwest around 8:30pm BST on Monday, 17 September can see the 8-day-old Moon just 1¾ degrees to the upper left of magnitude +0.4 Saturn in deep twilight. Both the ringed planet and the Moon will fit comfortably in the field of view of binoculars and small telescopes at magnifications less than about 25×, but you’ll need a telescope magnifying at least twice that if you wish to see the planet’s ring system clearly.
Saturn was at opposition on 27 June, so observers in northern temperate latitudes such as the UK are now seeing the planet setting in the west-southwest four hours after the Sun. If you wish to make any observations of the ringed planet you need to be ready as soon as the sky’s dark enough to see it, a task made much easier by the Moon’s proximity on the night in question.
The UK evening of 17 September finds Saturn almost 9.88 astronomical units or 1,478 million kilometres from Earth, some 3690 times farther away than our waxing gibbous Moon almost in the same line of sight. This is also a good evening to spot Saturn’s largest and brightest moon, magnitude +9.3 Titan, since it lies close to greatest easterly elongation from its parent planet. See the graphic below for the configuration of the brighter Saturnian moons this night.The aspect of Saturn and its brightest moons Titan and Rhea, with lesser moons Tethys and Dione for larger backyard ‘scopes, on the UK night of 17 September 2018. Observers with Newtonian/Dobsonian telescopes should rotate this image through 180 degrees to match their eyepiece view, while users of refractors and catadioptrics (Schmidt- and Maksutov-Cassegrains) with a star diagonal need to mirror this graphic left-right to replicate what they see through the eyepiece. AN graphic by Ade Ashford.
NASA’s Cassini spacecraft watched clouds of methane moving across the far northern regions of Saturn’s largest moon, Titan, on 29 and 30 October 2016. Several sets of clouds develop, move over the surface and fade during the course of a movie sequence spanning 11 hours, with one frame taken every 20 minutes. These clouds are measured to move at a speed of about 14 to 22 miles per hour.
On Saturday 27 August at 22:32 UT (11:32pm BST), a spectacularly close conjunction occurs between Jupiter and Venus just 22 degrees west of the Sun in the constellation of Virgo, when the planetary pair are just 4 arcminutes, or one-fifteenth of a degree, apart. Here is our guide to the best locations and times to view this rare event.
Mercury attains a greatest easterly elongation of 18 degrees from the Sun on 15 March, the innermost planet’s best evening showing for Northern Hemisphere observers for the entire year. From 12–20 March, planets Mercury and Venus remain just 4 degrees apart low in the west 45 minutes after sunset as seen from the British Isles.
