Several impressive phenomena can be observed in the sky. Among these are the comets, which move around the Sun on elongated paths. For us they become visible quite suddenly, when they draw close to the Sun and reflect its light. Some comets, such as Halley's comet, which was first observed in 1066, return periodically. When approaching the Sun, comets form a tail of dust and gas.
Asteroids, another class of celestial objects, are found mainly in the region between Mars and Jupiter. They have different sizes and are made up of rock and metal.
Countless numbers of meteorites move within our solar system. They range from a few millimeters to several kilometers in diameter. When small meteorites penetrate the Earth's atmosphere, they are vaporized and create a glowing trail we know as a meteor or shooting star. If a meteorite passes through the atmosphere and actually strikes the surface, it creates an impact crater.
The space between the planets is filled with gas and dust. This is called interplanetary matter. The particles in the areas between individual stars and galaxies, such as those found in the various nebulae, are known as interstellar matter.
