On Thursday, March 12th, the waning gibbous Moon and Saturn are just 2° apart in northern Scorpius during dawn astronomical twilight for observers in the British Isles. AN graphic by Ade AshfordEarly risers in the British Isles on Thursday, March 12th have an observing treat in the form of a close conjunction between the 20-day-old waning gibbous Moon and ringed planet Saturn in the constellation of Scorpius low to the south at 5 am GMT. The pair will be separated by just 2°, so they can be seen in the same field of view of virtually any binocular — or, indeed, telescopes magnifying 20x or less.
This computer simulation of the appearance of Saturn on the morning of March 12th is the kind of view reserved for powerful telescopes at very high magnifications. However, the rings themselves can be detected with small telescopes at powers of 50x or more. The north face of the rings is tipped in our direction (the illustration has north up and east to the left), so users of Newtonian telescopes should invert the image. AN graphic by Ade Ashford/StellariumDespite its low altitude as seen from the British Isles, Saturn is particularly attractive in a telescope at the present time since its rings are widely tilted in our direction with the planet’s northern hemisphere on show.
Gas giant Saturn is the Solar System’s second largest planet after Jupiter and its globe is nine times the diameter of Earth. The rings are composed of countless millions of icy moonlets ranging in size from specks of dust to around 10 metres in diameter, all orbiting Saturn in a 20-metre-thick plane, extending from 4,100 miles (6,600 kilometres) to 75,000 miles (120,700 km) above the planet’s equator.
If you notice some starlike points of light close to Saturn in your telescope, these will be the planet’s moons. The brightest is 9th magnitude Titan closely followed by 10th magnitude Rhea. On the morning of March 12th, Titan will lie slightly more than four ring diameters to the west of Saturn, which is to the left of the planet in Newtonian telescopes and refractor/Schmidt-Cassegrain/Maksutov-Cassegrain telescopes with a star diagonal. Clear skies!
Observers in Western Europe should look to the east an hour before sunrise on Monday, 18 September to see not only dazzling Venus and the old crescent Moon in the same binocular field of view, but planets Mars and Mercury against the stars of Leo too.
Tethys appears to be peeking out from behind Rhea in this image from the Cassini probe. Scientists believe that Tethys’ surprisingly high albedo is due to the water ice jets emerging from its neighbour, Enceladus.
In the pre-dawn twilight of Tuesday, 1 March, the 21-day-old waning gibbous Moon acts as a convenient celestial guide to planets Saturn and Mars. For observers in the centre of the British Isles, the best time to see this triple conjunction is shortly before 6am GMT, when the trio are highest in the sky to the south.
