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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 .
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 ...
With a mean orbital speed around the barycentre of 1.022 km/s (2,290 mph), the Moon covers a distance of approximately its diameter, or about half a degree on the celestial sphere, each hour. [ 6 ] The Moon differs from most regular satellites of other planets in that its orbital plane is closer to the ecliptic plane instead of its primary 's ...
Semi-synchronous orbit: An orbit with an orbital period equal to half of the average rotational period of the body being orbited and in the same direction of rotation as that body. For Earth this means a period of just under 12 hours at an altitude of approximately 20,200 km (12,544.2 miles) if the orbit is circular. [16]
The period of the resultant orbit will be less than that of the original circular orbit. Thrust applied in the direction of the satellite's motion creates an elliptical orbit with its highest point 180 degrees away from the firing point. The period of the resultant orbit will be longer than that of the original circular orbit.
The orbital period distinction is of importance in the evaluation of the risk from near-Earth comets because short-period NECs are likely to have been observed during multiple apparitions and thus their orbits can be determined with some precision, while long-period NECs can be assumed to have been seen for the first and last time when they ...
This is due to the solar day being shorter than the sidereal day for retrograde rotation, as the rotation of the planet would be against the direction of orbital motion. If a planet rotates prograde, and the sidereal day exactly equals the orbital period, then the formula above gives an infinitely long solar day (division by zero).
With the exoplanet sample known in 2009, a group of astronomers estimated that "(1) around 35% of the published eccentric one-planet solutions are statistically indistinguishable from planetary systems in 2:1 orbital resonance, (2) another 40% cannot be statistically distinguished from a circular orbital solution" and "(3) planets with masses ...