The Geminid meteor shower is set to peak on Friday, December 14th. The Geminid meteor shower occurs when the Earth passes through a debris cloud left by near-earth object (NEO) 3200 Phaethon, which, interestingly is not a comet, but an asteroid, some theorists think.
Asteroids don't normally spew debris into space. The tail of a comet leaves debris sometimes as small as a grain of sand that when they come into contact with Earth's atmosphere become a bright flash of light streaking across the sky: a meteor. So where in the world does the debris that forms the Geminids come from?
Some think that the asteroid collided with another NEO that creates a cloud of dust and debris that follows it around in its orbit. Some think that it is actually an extinct comet. The comet's orbit is highly elliptical, like a comets. It comes extremely close to the Sun, twice as close as Mercury, where repeated blasts of solar energy could have reduced it to the rocky comet core we see today.
True to astronomical acronym fashion, this NEO is also classified as a PHA, or Potentially Hazardous Asteroid, because it comes a mere 2 million miles away from Earth's orbit. The size of this asteroid is 5 km wide; half the size of the asteroid assumed to have made the dinosaurs extinct.
3200 Phaethon is visible with a telescope in the constellation Virgo, where it will be 11 million miles away from Earth on December 10th. It appears as a magnitude 14 object not visible to the naked eye.
The meteor showers radiant is just "above" the star Castor, depending on what angle you are observing from.
A pretty sweet animation of the radiant and estimate of the meteors can be found on the incredibly cool Shadow & Substance website. This place has tons of cool fluid animations that can be used to illustrate tons of different things, so I encourage you to check it out.