As darkness falls in the UK on Thursday, 18 October 2018, the waxing gibbous Moon lies just 3¼ degrees from the Red Planet, making for a nice juxtaposition in typical binoculars as depicted above. AN graphic by Ade Ashford.Anyone in Western Europe blessed with clear skies at dusk on Thursday, 18 October should cast their gaze towards the 9-day-old Moon that happens to appear close to Mars in the southern sky. Their proximity is merely a line-of-sight effect since the Moon is just 401,600 kilometres distant, whereas the Red Planet lies almost 105 million kilometres from Earth this night, hence Mars is 260 times farther away.
Mars was closest to Earth just three-and-a-half months ago when its bright ochre disc spanned an impressive 24.3 arcseconds. Now, the Red Planet’s disc measures 13.4 arcseconds – little more than half its opposition best. However, many keen Mars observers will recall the global dust storm that obliterated much of the keenly anticipated surface detail from view. Thankfully, the martian atmosphere is much clearer now, so prominent features should be easier to detect despite the planet’s shrinking apparent size.UK dusk on 18 October 2018 finds Mars almost 12 weeks past opposition, hence it’s much farther away (some 105 million kilometres) and consequently smaller. On this night the Red Planet’s disc measures just 13.4 arcseconds across and shows an appreciable phase. Magnitude -0.9 Mars is highest in the southern sky of the British Isles close to 8:30pm BST when the dark Syrtis Major feature lies north of the planet’s equator, with the brighter Hellas plain nearer the south polar cap. Users of Newtonian reflectors should invert this graphic to match their eyepiece view, while those observing with refractors and catadioptrics with a star diagonal need to mirror the illustration left-right to match what they see. AN illustration by Ade Ashford.For skywatchers in the British Isles, darkness falls around 8pm BST on 18 October 2018 and Mars is best placed for observation in the southern sky about half an hour later. Even so, the Red Planet barely attains an altitude of 17 degrees – slightly less than the span of an outstretched hand at arm’s length – as seen from the heart of the UK.
The martian longitude facing Earth at 8:30pm BST this night is 309 degrees, hence prominent features such as the dark V-shaped Syrtis Major in the planet’s northern hemisphere, the bright Hellas basin in the south (see our interactive Mars Mapper web app for annotated maps of the planet) and the shrinking martian south polar cap will be on show for those with good seeing. Note, too, that Mars now has an appreciable phase; the planet’s disc is 87 percent illuminated on the night in question.
The Israeli Beresheet lander, while braking into orbit around the Moon 4 April, beamed back stunning views of lunar farside, giving a hint of what to expect after landing 11 April.
All five of the bright naked-eye planets are observable in the pre-dawn sky from about the third week of January 2016, particularly if one lives south of the equator. But even from the UK, you can get to view the spectacle if you time it right — and the weather obliges! The last time that Mercury, Venus, Mars, Jupiter and Saturn appeared in the same sky was 11 years ago.
Jupiter is now less than a month from opposition (7 April), so it’s very much open season for the Solar System’s largest planet. If you’re unsure where to find it, the rising 17-day-old waning gibbous Moon passes just two degrees from Jupiter on the UK evening of 14 March. Virgo’s brightest star, first-magnitude Spica, makes it a great binocular triumvirate.
