On this morning, just 2½ percent of the Moon’s visible hemisphere will be illuminated by sunlight, but the remainder of the lunar disc will be seen to be suffused with a faint glow called earthshine. This is merely sunlight reflected from the nearly fully illuminated Earth back onto the Moon. Telescope and binocular users will have no difficultly in detecting the vast, dark basaltic plans — the lunar ‘seas’, or maria — by earthshine.
On the UK morning of 18 October, planet Venus shines at magnitude -3.9 and presents a 94 precent illuminated disc just 10.7 arcseconds in angular size. This means that a telescope magnification of 175x is required to enlarge Venus to the same size as the adjacent Moon appears to the unaided eye.
For the keen-eyed among you, another morning planet is visible just under a span of a fist at arm’s length to the upper right of Venus. This is magnitude +1.8 Mars, so observers in the British Isles shouldn’t leave it much later than 6:45am BST to try locating the Red Planet with the naked eye or the growing twilight will drown it out. Some 190 times fainter than Venus on 18 October, Mars is a tiny 3.8 arcseconds in size — much too far away for any detail to be seen in backyard telescopes.
While you are looking at the Red Planet, see if you can also spot magnitude +3.5 star beta (β) Virginis (aka Zavijava) about a lunar diameter to the lower right of Mars this morning. Despite the Bayer designation beta, Zavijava is actually the fifth brightest star in the constellation of Virgo. It is a class F9 V main-sequence star about 36 light-years distant.
