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The orbital period (also revolution period) is the amount of time a given astronomical object takes to complete one orbit around another object. In astronomy , it usually applies to planets or asteroids orbiting the Sun , moons orbiting planets, exoplanets orbiting other stars , or binary stars .
Orbital decay is a gradual decrease of the distance between two orbiting bodies at their closest approach (the periapsis) over many orbital periods. These orbiting bodies can be a planet and its satellite , a star and any object orbiting it, or components of any binary system .
At present, the rate of axial precession corresponds to a period of 25,772 years, [3] so sidereal year is longer than tropical year by 1,224.5 seconds (20 min 24.5 s, ~365.24219*86400/25772). Before the discovery of the precession of the equinoxes by Hipparchus in the Hellenistic period , the difference between sidereal and tropical year was ...
The square of the orbital period of a planet is directly proportional to the cube of the semi-major axis of its orbit. Kepler published the first two laws in 1609 and the third law in 1619. They supplanted earlier models of the Solar System, such as those of Ptolemy and Copernicus. Kepler's laws apply only in the limited case of the two-body ...
Orbital characteristics the six parameters of the Keplerian elements needed to specify that orbit uniquely. Orbital period as defined here, time it takes a satellite to make one full orbit around the Earth. Perigee is the nearest approach point of a satellite or celestial body from Earth, at which the orbital velocity will be at its maximum ...
Note that the semi-major axis is proportional to the 2/3 power of the orbital period. For example, planets in a 2:3 orbital resonance (such as plutinos relative to Neptune) will vary in distance by (2/3) 2/3 = −23.69% and +31.04% relative to one another. 2 Ceres and Pluto are dwarf planets rather than major planets.
The orbital period is one-half of a sidereal day, i.e., 11 hours and 58 minutes, so that the satellites pass over the same locations [85] or almost the same locations [86] every day. The orbits are arranged so that at least six satellites are always within line of sight from everywhere on the Earth's surface (see animation at right). [ 87 ]
The Moon is Earth's only natural satellite.It orbits at an average distance of 384,400 km (238,900 mi), about 30 times the diameter of Earth. Tidal forces between Earth and the Moon have synchronized the Moon's orbital period (lunar month) with its rotation period at 29.5 Earth days, causing the same side of the Moon to always face Earth.