planet

(noun)

A large body which directly orbits any star (or star cluster) but which has not attained nuclear fusion.

Related Terms

Examples of planet in the following topics:

  • Kepler's Second Law

    • A line joining a planet and the Sun sweeps out equal areas during equal intervals of time .
    • In a small time the planet sweeps out a small triangle having base line and height.
    • Now as the first law states that the planet follows an ellipse, the planet is at different distances from the Sun at different parts in its orbit.
    • When the planet is close to the Sun it has a larger velocity, making the base of the triangle larger, but the height of the triangle smaller, than when the planet is far from the Sun.
    • One can see that the planet will travel fastest at perihelion and slowest at aphelion.

  • Kepler's First Law

    • Kepler's first law is: The orbit of every planet is an ellipse with the Sun at one of the two foci.
    • The orbit of every planet is an ellipse with the Sun at one of the two foci.
    • The dwarf planet Pluto, discovered in 1929, has an eccentricity of 0.25.
    • For a planet orbiting the Sun, $r$ is the distance from the Sun to the planet and $\theta$ is the angle between the planet's current position and its closest approach, with the Sun as the vertex.
    • Kepler's first law states this fact for planets orbiting the Sun.

  • Satellites

    • It is technically correct to refer to a planet as a "satellite" of its parent star, though this is not common.
    • Formally classified natural satellites, or moons, include 176 planetary satellites orbiting six of the eight planets, and eight orbiting three of the five IAU-listed dwarf planets.
    • As of January 2012, over 200 minor-planet moons have been discovered.
    • Planets around other stars are likely to have natural satellites as well, although none have yet been observed.
    • Polar orbit: An orbit that passes above or nearly above both poles of the planet on each revolution.

  • Kepler's Third Law

    • Kepler's third law states that the square of the orbital period of a planet is directly proportional to the cube of the semi-major axis of its orbit.
    • The square of the orbital period of a planet is directly proportional to the cube of the semi-major axis of its orbit .
    • The third law, published by Kepler in 1619, captures the relationship between the distance of planets from the Sun, and their orbital periods.
    • where P is the orbital period of the planet and a is the semi-major axis of the orbit (see ).
    • Kepler's third law states that the square of the period of the orbit of a planet about the Sun is proportional to the cube of the semi-major axis of the orbit.

  • Escape Speed

    • Imagine a situation in which a spaceship that does not have a propulsion system is launched straight away from a planet.
    • Let us assume that the only significant force that is acting on the spaceship is the force of gravity from the planet.
    • Where $G$ is the universal gravitational constant ($G = 6.67 \cdot 10^{-11} \text{m}^3\text{kg}^{-1}\text{s}^{-2}$), $M$ is the mass of the planet, $m$ is the mass of the spaceship, and $r$ is the distance of the spaceship from the planet's center of gravity.
    • Interestingly, if the spaceship were to fall to the planet from a point infinitely far away it would obtain a final speed of ses_e at the planet.
    • If the vehicle has a propulsion system to provide it with energy once it has left the surface of the planet, it is not necessary to initially meet escape speed requirements.

  • Dynamics of UCM

    • The Moon's orbit about Earth, the orbits of planets, asteroids, meteors, and comets about the Sun are other examples of gravitational orbits.
    • The orbit of each planet about the Sun is an ellipse with the Sun at one focus.
    • Each planet moves so that an imaginary line drawn from the Sun to the planet sweeps out equal areas in equal times.
    • Kepler's first law states this fact for planets orbiting the Sun.
    • Kepler's second law was originally devised for planets orbiting the Sun, but it has broader validity.

  • Heat Death

    • Stars are hotter than planets, for example, which are warmer than icy asteroids, which are warmer still than the vacuum of the space between them.
    • Most of these are cooling down from their usually violent births, at which time they were provided with energy of their own—nuclear energy in the case of stars, volcanic energy on Earth and other planets, and so on.

  • Visible Light

    • The Sun's luminosity function peaks in the visible range and light in that range is able to travel to the surface of the planet unattenuated due to the optical window.
    • The surface of the planet then emits energy primarily in infrared wavelengths, which has much greater difficulty escaping (and thus causing the planet to cool) due to the opacity of the atmosphere in the infrared.

  • Defining Kinematics

    • Everything from a tennis match to a space-probe flyby of the planet Neptune involves motion.

  • Electrostatic Shielding

    • Faraday cages are limited in their effectiveness, and cannot block static and slowly varying magnetic fields, such as that of the planet Earth.