Hadley Rille on the Moon, seen by SMART-1
Copyright ESA/Space-X, Space Exploration Institute
This strangely meandering channel, carved on the Moon, is one of the most famous features on our nearest celestial neighbour. It shot to fame in July 1971 when the two astronauts of Apollo 15 drove their lunar rover to its very edge.
Known as Hadley Rille, the feature is named after the 18th century British mathematician and inventor John Hadley. In 1721, Hadley presented a telescope that used a non-spherical mirror to the Royal Society in London. Shaped as a parabola, the mirror avoided the aberration caused by a spherical mirror, and set the shape for all telescope mirrors to come.
Hadley Rille is thought to have been carved by an ancient lava flow, dating back just over 3 billion years to soon after the Moon formed. It stretches more than 120 km, up to 1500 m wide and more than 300 m deep in some places.
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