A comet is an icy small Solar System body that, when passing close to the Sun, warms and begins to release gases, a process called outgassing.
The Solar System is the gravitationally bound system comprising the Sun and the objects that orbit it, either directly or indirectly.
A small Solar System body is an object in the Solar System that is neither a planet, nor a dwarf planet, nor a natural satellite.
Outgassing is the release of a gas that was dissolved, trapped, frozen or absorbed in some material.
Super Comet Part 1 - The Impact by Free Documentary
This produces a visible atmosphere or coma, and sometimes also a tail.
Comet (On-Ride) Hersheypark by Sharp Productions
These phenomena are due to the effects of solar radiation and the solar wind acting upon the nucleus of the comet.
An ion is an atom or a molecule in which the total number of electrons is not equal to the total number of protons, giving the atom or molecule a net positive or negative electrical charge.
Solar irradiance is the power per unit area received from the Sun in the form of electromagnetic radiation in the wavelength range of the measuring instrument.
The solar wind is a stream of charged particles released from the upper atmosphere of the Sun, called the corona.
Comet nuclei range from a few hundred metres to tens of kilometres across and are composed of loose collections of ice, dust, and small rocky particles.
The nucleus is the solid, central part of a comet, popularly termed a dirty snowball or an icy dirtball.
Water ice could refer to:
The coma may be up to 15 times the Earth's diameter, while the tail may stretch one astronomical unit.
Earth is the third planet from the Sun, the densest planet in the Solar System, the largest of the Solar System's four terrestrial planets, and the only astronomical object known to harbor life.
If sufficiently bright, a comet may be seen from the Earth without the aid of a telescope and may subtend an arc of 30° across the sky.
A telescope is an optical instrument that aids in the observation of remote objects by collecting electromagnetic radiation.
Comets usually have highly eccentric elliptical orbits, and they have a wide range of orbital periods, ranging from several years to potentially several millions of years.
In astrodynamics or celestial mechanics, an elliptic orbit or elliptical orbit is a Kepler orbit with an eccentricity of less than 1; this includes the special case of a circular orbit, with eccentricity equal to 0.
The orbital period is the time taken for a given object to make one complete orbit around another object.
Short-period comets originate in the Kuiper belt or its associated scattered disc, which lie beyond the orbit of Neptune.
The scattered disc is a distant circumstellar disc in the Solar System that is sparsely populated by icy small solar system bodies, and are a subset of the broader family of trans-Neptunian objects.
The Kuiper belt, occasionally called the Edgeworth–Kuiper belt, is a circumstellar disc in the outer Solar System, extending from the orbit of Neptune to approximately 50 AU from the Sun.
Long-period comets are thought to originate in the Oort cloud, a spherical cloud of icy bodies extending from outside the Kuiper belt to halfway to the nearest star.
The Oort cloud, named after the Dutch astronomer Jan Oort, sometimes called the Öpik–Oort cloud, is a theoretical cloud of predominantly icy planetesimals proposed to surround the Sun to as far as somewhere between 50,000 and 200,000 AU.
Tar is a dark brown or black viscous liquid of hydrocarbons and free carbon, obtained from a wide variety of organic materials through destructive distillation.
Long-period comets are set in motion towards the Sun from the Oort cloud by gravitational perturbations caused by passing stars and the galactic tide.
In astronomy, perturbation is the complex motion of a massive body subject to forces other than the gravitational attraction of a single other massive body.
A galactic tide is a tidal force experienced by objects subject to the gravitational field of a galaxy such as the Milky Way.
Hyperbolic comets may pass once through the inner Solar System before being flung to interstellar space.
Outer space, or just space, is the expanse that exists between celestial bodies, including Earth.
The appearance of a comet is called an apparition.
Comets are distinguished from asteroids by the presence of an extended, gravitationally unbound atmosphere surrounding their central nucleus.
This atmosphere has parts termed the coma and the tail.
However, extinct comets that have passed close to the Sun many times have lost nearly all of their volatile ices and dust and may come to resemble small asteroids.
Extinct comets are comets that have expelled most of their volatile ice and have little left to form a tail or coma.
Asteroids are thought to have a different origin from comets, having formed inside the orbit of Jupiter rather than in the outer Solar System.
The discovery of main-belt comets and active centaur minor planets has blurred the distinction between asteroids and comets.
Main-belt comets are bodies orbiting within the asteroid belt that have shown comet-like activity during part of their orbit.
As of November 2014 there are 5,253 known comets, a number that is steadily increasing as they are discovered.
However, this represents only a tiny fraction of the total potential comet population, as the reservoir of comet-like bodies in the outer Solar System is estimated to be one trillion.