The Geminids are one of the big deal meteor showers that happen every year. In fact, they're regarded as one of the most reliable and impressive. They're also a little strange.
Most meteor showers happen when Earth and a comet cross paths, slingling rocks, dust, and debris from the comet's tail into our atmosphere. The sudden influx of shooting starts that results is a highly noticeable event and humans have been recording them for millennia.
The Geminids are different. They sort of just appeared, seemingly out of nowhere, back in 1862. And it wasn't until the 1980s that scientists were finally able to identify the thing that was producing them. At which point, ish got weirder.
That's because the object, known as 3200 Phaethon, is really confusing. It doesn't seem to be a comet. At least, not a normal, healthy, functioning comet. It doesn't even have a tail. In fact, at this point most scientists think it's probably an asteroid, which then leads to still-yet-unexplained question of where all the meteors come from. Asteroids, after all, do not typically accumulate tails of small rocks. So far, the best guess has to do with 3200 Phaethon's orbit, which over the course of about a year and a half takes it closer to the Sun than Mercury and then back out further from the Sun than Mars. Those wild temperature swings might lead to the asteroid cracking and throwing off dust and debris, which then becomes meteors. But, as a NASA info page pointed out in 2010, that explanation doesn't totally cut it.
The amount of dust 3200 Phaethon ejected during its 2009 sun-encounter added a mere 0.01% to the mass of the Geminid debris stream—not nearly enough to keep the stream replenished over time.
According to the International Meteor Organization, you can expect the Geminids to peak tomorrow night, around 5:30 pm, Central Time. But this is a big shower, so you're likely to see something even if you can't hit the exact peak.
Also: While you're watching for meteors, also keep an eye out for an upcoming feature here by Miles O'Brien, which will delve into the latest in Geminid science!
Make use of The Bad Astronomy guide to meteor watching