Page 76 - All About Space 68 - 2017 UK

STARGAZER

Top tip!

The Straight Wall is
easiest to see when it
is near the terminator
(the line between
night and day).

Moon tour

Rupes Recta

‘The Straight Wall’

How to find the most dramatic
© ESO; B. Tafreshi
cliff on the face of the Moon…

If you have a small telescope or a around 450 metres (0.28 miles), it’s in the southwestern sky after sunset, offer the best views, the higher the
powerful pair of binoculars and look to roughly as tall as the London Eye, or to the upper left of Saturn. On that magnification the better.
the lower left of the great triple crater two nuclear submarines balanced end evening, with sunlight illuminating it All too soon Rupes Recta will be lost
chain of Ptolemaeus, Alphonsus and to end. Although the Straight Wall gives from the east, the cliff face will be in from view, as local sunset plunges it into
Arzachel, you will see (depending on the the impression of being a towering cliff shadow and appear as an obvious short, darkness. By 15 September it will be lost
time of the month) either a short, dark face, it’s not. Pre-Apollo space artists dark line to the lower left of Arzachel, in shadow, hidden from our gaze until
line or a short, bright line. depicted the Straight Wall as vertical, a very close to a small, deep pit of a crater just a fortnight later, coming back into
Moon atlases and phone apps identify frozen tsunami wave of grey lunar stone, called Birt. As sunlight creeps across view from 29 September.
it as ‘Rupes Recta.’ It doesn’t look much but if you stood at the base you would the Moon’s face and the cliff’s shadow One day in the future astronauts
at first glance, nothing more than a see the slope rising at an angle of only retreats, the Straight Wall will slowly will surely come to the top of the
dark pencil line or a white chalk scratch 30 degrees or so. turn into a bright line which seems to Straight Wall, and gaze down on the
drawn on the Moon’s ash grey face, but Rupes Recta doesn’t turn out to be sink down into the Moon, becoming Moon’s magnificent desolation from its
Rupes Recta has another name, and is very wide, or very high; so what’s all harder and harder to see until it’s barely lofty heights. Until then, we can enjoy
one of the most famous and beloved the fuss about? Well, the Straight Wall’s visible when our natural satellite is full. gorgeous views of it from Earth, with the
features on the whole of the Moon – remaining claim to fame is that it’s The best time to see the Straight Wall most modest observing equipment.
‘The Straight Wall’. very long. Stretching more than 110 will be after midnight on 12 September,
Of course, it’s not actually a wall; kilometres (68.3 miles) across the lunar when the Moon has just passed Last
it wasn’t built by tea-gulping lunar surface, it would reach from London to Quarter and is shining between the
labourers leaning on shovels! Rupes the Isle of Wight if placed on the Earth, famous Pleiades and Hyades star
Recta was built by the forces of nature, or from Carlisle to Edinburgh if you clusters of Taurus. Now illuminated
it is an enormous scarp, a region where prefer a more northerly comparison. from the west, Rupes Recta’s cliff face
part of the Moon’s surface dropped That’s so long it would have taken will be bathed in full sunshine, making
dramatically away, forming a steep cliff. Apollo astronauts more than eight hours it appear as a strikingly bright line
The cliff itself is very narrow, barely a to trundle and bounce from one end to etched into the darker surface of the
couple of kilometres wide and nowhere the other in the lunar rover, which was Moon – looking as if it has been dug out
near as wide as the terraced rims of used on the Moon in the later missions. of the ancient frozen lava flows of Mare
those three giant craters blasted out of The Straight Wall will first become Nubium by the tip of a knife’s blade. At
the Moon to its north. It’s not all that visible on 30 August, when the Moon is this time it will be visible with a good
tall either: with a maximum height of just past its First Quarter phase and low pair of binoculars, but telescopes will

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