Observers in the British Isles with an unobscured view of the southwest horizon should direct their telescopes at the setting 4-day-old crescent Moon by 7:40pm, for if skies are clear you may get a chance to see magnitude +3.9 star gamma (γ) Librae (aka Zuben Elakrab in Arabic) slip behind the darkened lunar hemisphere. The time at which this occultation occurs is just before 7:55pm in London, or 7:45pm in Edinburgh (all times quoted in this article are in British Summer Time). AN graphic by Ade Ashford/Stellarium.A waxing crescent Moon sliding serenely toward the horizon in evening twilight is always a pleasant sight to behold, but observers in the UK watching the 4-day-old Moon through a telescope around 40 minutes after sunset on Sunday, 24 September have an additional treat in store. The lunar crescent lies in the zodiacal constellation of Libra (the Scales) and passes in front of naked-eye star gamma (γ) Librae, also known by its Arabic name of Zuben Elakrab, soon after 7:45pm BST — though the precise time depends on where you live in the British Isles.
For observers in the London area, the magnitude +3.9 star winks out behind the darkened lunar hemisphere shortly before 7:55pm, while skywatchers closer to Edinburgh will see the occultation occur at 7:45pm BST. For observers nearer the centre of the British Isles, the event happens close to 7:49pm when the 20 percent illuminated Moon lies just 9 degrees — barely the span of a fist held at arm’s length — above the southwest horizon.
Gamma Librae lies about 160 light-years from Earth. Interestingly, it is also a double star, though its magnitude +11 companion some 42½ arcseconds distant will not be visible owing to the glare from the adjacent Moon and atmospheric extinction so close to the horizon. Furthermore, the star’s reappearance at the bright lunar limb close to 8:55pm BST is unlikely to be seen so close to moonset.
Sunday 6 November marks exactly 24 weeks since planet Mars was at opposition in the summer sky. It is also the date when you can see the Red Planet close to the six-day-old waxing crescent Moon low in the southern sky an hour after sunset in the British Isles and Western Europe.
On the morning of Wednesday, 6 April experienced observers in the British Isles with a clear sky living south of a line drawn between Galway in Ireland, Dumfries in Scotland and Berwick-upon-Tweed in Northumberland can potentially observe planet Venus slip behind the northern polar regions of the 28-day-old waning crescent Moon. But beware: the Sun lies just 16 degrees away.
The Moon’s thin atmosphere contains neon, a gas commonly used in electric signs on Earth because of its intense glow. While scientists have speculated on the presence of neon in the lunar atmosphere for decades, NASA’s Lunar Atmosphere and Dust Environment Explorer (LADEE) spacecraft has confirmed its existence for the first time.
