The beautiful ringed planet Saturn has arrived at its closest approach to Earth of the year.
On 14 August, Saturn is 8.86 astronomical units from Earth. An astronomical unit is the radius of Earth’s orbit around the sun. Equal to roughly 150m km, that places Saturn 1.3bn km away currently. Travelling at an average speed of 9.69km a second, Saturn takes roughly 29.5 years to complete a single orbit of the sun. Moving almost three times as quickly, Earth undertakes Saturn every 378 days, passing directly between it and the sun.
Seen from Earth, Saturn is centred in the opposite side of the sky to the sun, hence astronomers call this close pass “opposition”. As Earth catches up and glides past Saturn, our perspective makes the distant planet appear to temporarily backtrack across the backdrop of stars. For a few months, instead of its usual eastward motion through the constellations, the planet moves westward. This apparent “retrograde” motion began on 4 June and will last until 23 October.
The chart shows the view looking due south at 0100 BST on 16 August. From Sydney, Australia, the planet appears due north at about midnight.