I conduct sky tours during periodic astronomy events held at High Bridge Trail State Park (Virginia). One of the most popular programs is an annual gathering to observe the Geminid meteor shower, which peaks in mid-December. This year's Geminid meteor shower will reach its highpoint during the night of December 13–14. Although the near-full waxing moon may wash out some of the dimmer meteors, the Geminids are famous for producing brighter meteors than some of the year's other showers. With luck, some of the most brilliant will still put on a show.
In ancient times, people did not know what caused meteors. Often, they were thought of as stars voluntarily leaving an assigned place in the heavens—or being forcefully expelled. In some cultures, a shooting star was viewed as a messenger of good fortune; in others, a falling star was seen as an omen of bad things to come.
Today, astronomers offer an explanation devoid of mystery. Meteors occur when the earth's orbit causes its atmosphere to encounter specks of space dust and debris left by comets or other cosmic bodies that have crossed the earth's path. When these miniscule bits hit the earth's atmosphere, friction causes them to be vaporized. This process creates a fleeting trail of visible light. Occasionally, larger pieces do not burn up entirely, and fragments of space rock make it all the way to the ground. These kinds of rocks are called meteorites.
Some of the regularly occurring meteor showers have been linked to the passage of specific objects. The Perseid shower in mid-August sparkles with the dust left behind by comet Swift-Tuttle. The Eta Aquarids in May and the Orionids in October occur at the points where Halley's comet crosses the earth's orbit every 75 years (plus a few months). The Quadrantid shower in January and the Geminid shower in December are both associated with asteroids.
Although a scientific explanation offers essential details, it doesn't account for the thrill people experience when they see a meteor. Dates for anticipated showers can be pinpointed, but the appearance of each individual meteor remains an unpredictable surprise.
To view this year's Geminid meteor shower, pick a safe and comfortable dark spot and look up. It may help to look in a direction away from the bright moon. Although all of the meteors will have a trajectory that originates within the constellation Gemini, the meteors themselves can appear at any point. Be prepared to be startled. Be prepared for oohs and aahs as a straightforward astronomical phenomenon displays its more enigmatic character.