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WASP-17b is thought to have a retrograde orbit (with a sky-projected inclination of the orbit normal against the stellar spin axis of about 149°, [11] not to be confused with the line-of-sight inclination of the orbit, given in the table, which is near 90° for all transiting planets), which would make it the first planet discovered to have such an orbital motion.
Diagram of modern conception of the Counter-Earth, a planet in the same orbit as the Earth, but 180° out of phase. Philolaus's ideas were all eventually superseded by the modern realization that a spherical Earth rotating on its own axis was one of several spherical planets following the laws of gravity and revolving around a much larger Sun ...
The orbit of a planet is an ellipse with the Sun at one of the two foci. A line segment joining a planet and the Sun sweeps out equal areas during equal intervals of time. The square of a planet's orbital period is proportional to the cube of the length of the semi-major axis of its orbit.
In Mercury's case, the planet completes three rotations for every two revolutions around the Sun, a 3:2 spin–orbit resonance. In the special case where an orbit is nearly circular and the body's rotation axis is not significantly tilted, such as the Moon, tidal locking results in the same hemisphere of the revolving object constantly facing ...
The first panel (left) of this artist's concept depicts how Uranus' protective magnetosphere behaved prior to Voyager 2's flyby. The second panel shows that unusual solar weather was happening at ...
All eight planets in the Solar System orbit the Sun in the direction of the Sun's rotation, which is counterclockwise when viewed from above the Sun's north pole. Six of the planets also rotate about their axis in this same direction. The exceptions – the planets with retrograde rotation – are Venus and Uranus.
This period, typically given in hours, and sometimes called rotation rate or spin rate, is a fundamental standard physical property for minor planets. In recent years, the periods of many thousands of bodies have been obtained from photometric and, to a lesser extent, radiometric observations.
Earth’s inner core, a red-hot ball of iron 1,800 miles below our feet, stopped spinning recently, and it may now be reversing directions, according to an analysis of seismic activity.