Apollo 15 lunar soil experiment, August 1971. US Astronaut James Irwin using a scoop to make a trench in the lunar soil during the Apollo 15 second lunar surface extravehicular activity (EVA-2). The base of Mount Hadley in the background is 14 kilometres distant. At left is a piece of equipment called a gnomon. This trench was dug near the ALSEP (Apollo Lunar Surface Experiments Package) site (Station 8 near the lander), and was used for soil mechanics measurements. A hard layer under the soil was present at a depth of about half a metre. Apollo 15 was the fourth manned mission to land on the Moon. The lunar lander 'Falcon' touched down in the Hadley region of the Moon on 30 July 1971. Astronauts David Scott and James Irwin spent a total of 18.5 hours outside their spacecraft, carrying out three exploration trips (EVAs) with the Lunar Roving Vehicle. Photographed by Scott on 2 August 1971.