Perigee is the point in an orbit of a celestial body where it is closest to Earth. It applies to any object, such as the Moon or a satellite, that is orbiting our planet.
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Perigee occurs because most orbits are elliptical rather than circular.
The opposite of perigee is apogee, where the orbiting body is farthest from Earth.
The distance at perigee can influence tidal forces on Earth.
The term 'perigean spring tide' refers to higher-than-normal tides that occur when the full moon or new moon coincides with perigee.
Perigee distance can vary due to gravitational influences from other celestial bodies and orbital eccentricity.
Review Questions
What is perigee and how does it differ from apogee?
How does the occurrence of perigee affect tides on Earth?
Why do distances at perigee vary over time?
Related terms
Apogee: The point in an orbit where a celestial body is farthest from Earth.
Elliptical Orbit: An orbit in the shape of an ellipse, which has two focal points including one occupied by the central body around which another body revolves.
Orbital Eccentricity: A measure of how much an orbit deviates from being circular, ranging between 0 (a perfect circle) and 1 (a parabolic trajectory).