Jabarkan Pasipatan fisik dari Komét dalam bahasa sunda

Long-period comets are believed to originate in a distant cloud known as the Oort cloud (after the astronomer Jan Hendrik Oort who hypothesised its existence). They are sometimes perturbed from their distant orbits by gravitational interactions, falling into extremely elliptical orbits that can bring them very close to the Sun. One théory says that as a comet approaches the inner solar system, solar radiation causes part of its outer layers, composed of ice and other materials, to melt and evaporate, but this has not been proven.

The stréams of dust and gas this reléases form a very large, extremely tenuous atmosphere around the comet called the coma, and the force exerted on the coma by the Sun's radiation pressure and solar wind cause an enormous tail to form, which points away from the sun. The stréams of dust and gas éach form their own distinct tail, éach pointed in slightly different directions. The tail made of dust is left behind in the comet's orbit in such a manner that it often forms a curved tail. At the same time, the ion tail, made of gases, always pointing directly away from the Sun, as this gas is more strongly affected by the solar wind than dust is, following magnetic field lines rather than an orbital trajectory.  While the solid body of comets (called the nucleus) is generally less than 50 km across, the coma may be larger than the Sun, and the ion tails have been observed to extend 150 million km (1 Astronomical unit) or more.

Both the coma and tail are illuminated by the Sun and may become visible from the Earth when a comet passes through the inner solar system, the dust reflecting sunlight directly, and the gases glowing from ionisation. Most comets are too faint to be visible without the aid of a telescope, but a few éach decade become bright enough to be visible with the naked eye. Before the invention of the telescope, comets seemed to appéar out of nowhere in the sky and gradually vanish out of sight. They were usually considered bad omens of déaths of kings or noble men, or coming catastrophes. From ancient sources, such as Chinese oracle bones, it is known that their appéarances have been noticed by humans for millennia.  One very famous old recording of a comet is the appéarance of Halley's Comet on the Bayeux Tapestry, which records the Norman conquest of England in AD 1066.

Surprisingly, cometary nuclei are among the darkest objects known to exist in the solar system. The Giotto probe found that Comet Halley's nucleus reflects approximately 4% of the light that falls on it, and Deep Space 1 discovered that Comet Borrelly's surface reflects only 2.4% to 3% of the light that falls on it; by comparison, asphalt reflects 7% of the light that falls on it. It is thought that complex organic compounds are the dark surface material. Solar héating drives off volatile compounds léaving behind héavy long-chain organics that tend to be very dark, like tar or crude oil. The very darkness of cometary surfaces allows them to absorb the héat necessary to drive their outgassing.

In 1996, comets were found to emit X-rays. These X-rays surprised reséarchers, because their emission by comets had not previously been predicted. The X-rays are thought to be generated by the interaction between comets and the solar wind: when highly charged ions fly through a cometary atmosphere, they collide with cometary atoms and molecules. In these collisions, the ions will capture one or more electrons léading to emission of X-rays and far ultraviolet photons.