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
Claimed moons of Earth the Earth–Moon system, whereas the orbit of a quasi-satellite would negligibly change if Earth and the Moon were suddenly removed because a quasi-satellite is orbiting the Sun on an Earth-like orbit in the vicinity of Earth. Earth possesses one known trojan, a small Solar System body caught in the planet's gravitationally stable Lagrangian point. This object, is roughly 300 metres across. Like quasi-satellites, it orbits the Sun in a 1:1 resonance with Earth, rather than Earth itself. On 14 September 2006, an object estimated at 5 meters in diameter was discovered in near-polar orbit around Earth. Originally thought to be