Meteors or shooting stars are tiny pieces of space rock, usually no bigger than a grain of sand, which crash through the Earth's upper atmosphere at tremendous speed. The friction against the air causes the meteor to burn up and create a brief streak of light.
At certain times of the year the Earth passes through the debris left behind by a comet. The comet may be long gone but the tiny pieces from the tail still remain in space. When this happens we get to see many meteors and it becomes a meteor shower or even a meteor storm. The meteors all appear to radiate from one particular area of the sky and so are named after the closest constellation. The Perseids, Leonids, Orionids and Geminids are all meteor showers that can sometimes produce hundreds of meteors per hour. The Geminids are different: while most meteor showers are the product of a comet the Geminids come from an asteroid known as 3200 Phaethon.
3200 Phaethon is big, about five miles wide; it orbits the Sun every 523 days. During its orbit it gets very close to the Sun, closer than any other asteroid, and then swings out further than Mars. Its path takes it across the Earth's orbit and the debris from it creates the Geminid meteor shower every year around the middle of December. Usually we are nowhere near as the asteroid passes by, but this year the asteroid will cross the Earth's orbit tomorrow night 16 December very close to the Earth. There is no danger of it hitting us but it may up the rate of meteors from the Geminid shower to possibly hundreds of meteors per hour.
You won't be able to see the asteroid with the naked eye - it's too small and too far away - but you will be able to see the meteor shower and as the moon will be out of the way this year, it could be quite a spectacular display. As the name implies, the Geminids appear to radiate from the constellation Gemini just above and to the left of Orion, about halfway up in the southern sky. The Geminids are a reliable shower producing some very bright shooting stars. Meteor showers don't require any special equipment to see them; just find a dark area away from streetlights and look up. Wrap up warmly and give your eyes 15 to 20 minutes to become dark-adapted and enjoy the show. It is best not to look directly at Gemini as meteors can appear anywhere in the sky. Try looking a little higher and to the sides of the constellation to see meteors with longer trails.