Comets are unsteady body, which usually include little not many kilometers in distance. When you are at a great distance from the Sun are down, its small core, which can vary from a few hundred meters to about 10 km. only reflects light. Near the sun the core is surrounded by a "head", the comma, whose diameter can be up to 30,000 km. The coma is composed of gas emerged from the nucleus by sublimation and dust. Its production increases severely as we advance the Sun.
The dust is accelerate by the solar wind pressure and thus forms in the plane of the orbit leaving a curved tail of the comet. The "plasma tail" that follows a direction opposite the sun can always be at a length of 100 million miles. These can be gas or powder being generally straight first and the second curves.
Several weak comets move around the sun king in times of a few years in elliptical orbits, Neck’s comet has a period of only 3.3 years. Very bright comets seen occasionally take many centuries to traverse their orbits around the sun, pass very close to this as opposed to short-period (which has their aphelia roughly the orbit of Jupiter) that are unspectacular.
The long-period comets have their aphelia by the orbit of Neptune while the long period has nearly as eccentric trajectories described parables.
Solar Observatory and Helioferico (SOHO) has observed a rare celestial event, two comets reducing into the solar atmosphere in close succession on June 2, 1998. This was followed by a dramatic ejection of gas and magnetic fields in the south-east sun. The observations of the comet and the great prominence were made by the coronagraph LASCO (Large Angle and spectrometric Coronagraph) carrying on board SOHO. Instruments of this ship have already discovered over 50 comets, among them some of the known "that touch the sun", but never in such close succession.
The two comets about to dive into our sun
Without doubt the most famous of comets is Halley has been seen regularly since before the Christian era. In 1682 appeared a bright comet, one of the observers was Edmond Halley who became Astronomer Royal, discovered he was remarkably similar to the comets of 1607 and 1531. He therefore suggested that it could be the same and predicted the next step in 1758. Halley had died by then but a fan called Politick watched on Christmas Eve 1758, before perihelion in March 1759. Sometimes it was spectacular, for example, in the year 837 BC the minimum distance to Earth was 10 million km. so its brightness was as remarkable as that of Venus and its tail extended over 93 ° in the sky.