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.
Skywatchers in the UK looking to the south-southwest at dusk on Monday, 17 September can see the waxing gibbous Moon just 1¾ degrees to the upper left of Saturn, the pair fitting comfortably in the same field of view of binoculars and small telescopes magnifying 25× or less. This is also a good night for spotting Titan, Saturn’s largest and brightest moon.
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.
A new study of satellite data finds that numerous volcanic deposits distributed across the surface of the Moon contain unusually high amounts of trapped water compared with surrounding terrains. The finding of water in these ancient deposits, which are believed to consist of glass beads formed by the explosive eruption of magma coming from the deep lunar interior, bolsters the idea that the lunar mantle is surprisingly water-rich.
