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
Full moon full moons rise around the time of sunset. Because the moon moves eastward among the stars faster than the sun its meridian passage is delayed, causing it to rise later each day – on average by about 50.47 minutes. The harvest moon and hunter's moon are unique because the time difference between moonrises on successive evenings is much shorter than average. The moon rises approximately 30 minutes later from one night to the next, as seen from about 40 degrees N or S latitude. (This is because a full moon in September appears to move not straight east but north-east