It is in this manner that the planetesimal hypothesis explains how the Sun, planets and Moons of the solar system are made. CHAPTER VIII SEEING THE STARS =How the Stars Shine.=—A burning match, a candle, an oil or gas flame, the Sun, comets and meteors all give out light and heat in exactly the same way, but the heat and light are made differently. When you strike a match the friction makes enough heat to light the chemicals of which the head is formed and the burning gases light the splint which in turn generates more gases from the wood and these give out more light and heat. When you light a candle the heat melts the wax which is then drawn up the wick, the burning gas around the wick produces more gas and the gas keeps the flame going. In the case of an oil lamp the oil, which is already a fluid, is drawn up by the wick, where it is changed into gases, and light and heat result as in the candle. The oil lamp is, then, a step ahead of the candle, for the solid wax is replaced by the fluid oil. In the gas light the gas, which is made of coal or other matter, is forced out of the jet under pressure and this gives a bigger and better flame than the oil lamp; and, as the oil lamp is better than the candle, so the gas jet is an improvement over the oil lamp. Now the Sun, and this is also true of most of the stars, is so large and hot that if any solid matter, such as iron and other metals could be thrown into the Sun they would not only be melted but instantly changed into gases. Further, the Sun is so hot that the materials cannot combine with Oxygen—in other words they cannot burn. The intensely hot gases of the Sun radiate the light and heat and we suppose that they keep themselves hot largely by contraction. When a comet comes close enough to the Earth to be seen it is then close enough to the Sun so that the light and heat of the Sun cause some of the gases of which the nucleus of the comet is formed, to become white hot; as a comet gets closer to the Sun the solid matter of the nucleus, such as sodium—which is a kind of salt—iron and other things are changed into gases and these burn fiercely. While we can see the light of a comet we cannot feel its heat, for a comet is too small to send its heat waves through such a great distance. Just as a match is lit by striking it, so meteors are set on fire by striking the air. Meteors are made up of the same kind of matter as comets and when these shooting stars come within the attraction of the Earth the friction caused by the meteor rubbing against the air is so great that an intense heat is produced and the gases burst into flame. If a meteor is small it is entirely burned up before it reaches the Earth and all we see of it is a bright streak of light. If a meteor is large enough only the outside of it is burned and it will, in consequence, reach the Earth, when it becomes, as explained in the last chapter, a meteorite.