Perigean spring tide Perigean spring tide A proxigean spring tide (also known as a perigean spring tide) is a tide that occurs three or four times per year when the Moon's perigee (its closest point to Earth during its 29.5-day elliptical orbit) coincides with a spring tide (when the Earth, Sun and Moon are nearly aligned every two weeks). This tide usually adds only a couple of inches to normal spring tides. The Moon's orbit around Earth is elliptical, which causes the Moon to be closer to Earth and farther away at different times. The Moon and the Sun are aligned every two
Journey of Apollo 15 to the Moon small risk that it could cause the spacecraft to depressurize. It was possible, in an emergency for the crew to spend the cruise back to Earth in their pressurized space suits. The major event of day 4 was Lunar Orbit Insertion (LOI). Occurring behind the Moon, out of contact with the Earth, this engine burn put the spacecraft into orbit around the Moon. It was the first test of the new procedures for using both SPS during a long burn. Loss of Signal (LOS) was at 78 hours, 23 minutes and 31 seconds GET as the spacecraft went behind the