In the early evening of Tuesday, April 21st, suitably equipped observers in the extreme northeast of Scotland with a clear sky can see a daylight occultation of Aldebaran, the brightest star in the constellation of Taurus, by the three-day-old waxing crescent Moon.
This all happens north of a line drawn between Kinlochbervie by Loch Inchard on the west coast and Latheron on the A9 to the east, so observers in Durness, Thurso, Wick and John o’ Groats on the mainland, or the Orkneys and Shetland Islands, will see the Moon completely cover the star by 6:20 pm BST.
Important note: please take extreme care looking for the Moon in daylight with a telescope lest you accidentally glimpse the Sun with tragic consequences for your eyesight. A computerised GoTo mount is highly recommended. If you must sweep with binoculars, ensure that the Sun is hidden behind a wall or building as the Moon lies just 39° to the Sun’s upper left.
Those that live (or plan to be) precisely on the graze line close to 6:25 pm BST will witness a rarer grazing occultation of Aldebaran — seeing the star appear to flicker on and off as the mountains and valleys of the Moon’s southern regions alternately cover then expose the star as the lunar orbital motion carries it by. The Moon and star will be some 40 degrees high in the southwest. [Note: observers in North America will also see a grazing daylight occultation of Aldebaran 15h28m—16h09m UTC as it passes through Arizona, New Mexico, Colorado, Kansas, Nebraska, Iowa, Wisconsin, Michigan, Ontario and Quebec.]
For the rest of us living further south in the British Isles, the Moon will miss Aldebaran entirely and we will see the 12% illuminated lunar crescent poised to the upper left of the star low to the west as dusk fades to dark.
Second only to the Moon as the brightest nighttime object, planet Venus is currently 1.066 astronomical units (93 million miles; 159 million kilometres) distant, shining at magnitude -4.1 and sporting a 71% illuminated gibbous disc approaching 16 arcseconds in diameter. This means that in a telescope, Venus will require a magnification of 120x to make it appear the same size as the Moon to the unaided eye.
Inside the magazine
You can find out more about the Moon and Venus in the April edition of Astronomy Now in addition to a full observing guide to the night sky.
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