er the action of the solar wind by a phenomenon where a proton removes an electron from an atom. The speed at which the ions are moving is what causes the tail to be straight. The light from the tail is emitted by fluorescence, which is a particle of solar wind that excites an electron of the atom or molecule concerned. This electron reaches a level at which it is stable, goes down again and releases its energy in the form of a photon, a particle of light, of a well determined energy and thus, of a specific color. When our solar system began, it was just a vast cloud of gas and dust. Several billion years ago, the cloud slowly rotated around the sun, which was very young, and particles within the cloud collided with one each other. During this time some objects were shattered by these collisions, while others grew in size and were to later become the planets. Throughout this early period, comets probably filled the solar system. Their collisions with the early planets played a major part in the growth and evolution of each of the planets. The ice that makes up comets seems to have been what formed the first atmospheres of the planets, and scientists now very strongly believe that it was the collisions of comets that brought water to our world, and made life able to begin. Over the years, comets actually became more rare within our solar system. They do not fill our skies as they did about 4 billion years ago. Also today, a comet that can be seen with the naked eye can be expected only about once in a whole decade. Astronomers with powerful telescopes can see many more comets, but even in this case it is still not common for as many as 15 or 20 comets to be able to be seen in the sky at one time. Today, most comets are located outside of our solar system in part of the original cloud of dust and gas that has stayed pretty much untouched for billions of years. These regions are called the Oort Cloud and the Kuiper Belt. The Dutch astronom...
