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Listen to the sound of falling meteors

A Geminid meteor shower, as portrayed by artist Duane Hilton  

(CNN) -- Hear something as this page loaded?

That was the radio echo of a Geminid meteor falling through Earth's atmosphere (If you didn't hear it, click here). The signal, as recorded by NASA's radio meteor detection system, can sound as mysterious as the origin of the Geminids themselves.

The echoes result from reflected radio waves, which bounce off the trails of fast-moving meteoroids. Each time a Geminid meteor blazes across the sky, the Marshall Space Flight Center in Alabama records an echo at its listening station. The radio meteor detection station can pick up 67 MHz video carrier signals from Channel 4 TV transmitters as radio signals from TV stations, RADAR facilities and AM/FM transmitters constantly bounce off short-lived meteor trails like the Geminids, according to NASA.


The only known meteor shower trailing an asteroid, the Geminids remain active from December 7 to 17 and reached their day-long peak Wednesday before dawn. While stargazers can usually see about 80 meteors per hour, they may have viewed about 20 to 30 per hour this year due to a nearly full moon that muted the Geminids' usual magnificence, according to NASA. Observers can watch a repeat show before dawn Thursday morning.

The yellow points of light streaking through the sky resemble other meteors, but their origin is decidedly different. A near-Earth asteroid called 3200 Phaethon spawns the meteor shower in its debris trail -- something asteroids don't usually have. Comets are the usual parents, with meteor showers becoming visible when Earth passes through a comet's debris trail.

sky map
The source of the Geminids is the radiant point of the constellation Gemini, about 60 degrees above the southern horizon at 4 a.m.  

Scientists theorize that a Phaethon's presence in the asteroid belt every 17 months may account for the debris trail, according to NASA. Phaethon is at its farthest point from the sun when it enters the belt, and a collision between Phaethon and a smaller object may have resulted in the debris stream. But other more detailed studies show that Phaethon may have released the meteoroids when it was close to the sun.

There is no mystery about the Geminids' visibility, which remains stable from year to year in mid-December. Rural observers will see more than suburban observers, but both will view the most before dawn Wednesday and Thursday morning. Geminids can appear anywhere in the sky, but their source will be the radiant point of the constellation Gemini, about 60 degrees above the southern horizon at 4 a.m.

In recent years the meteor shower has had a broad peak that slowly reaches two per minute before quickly dropping, according to Sky & Telescope magazine. In the 1940s, however, the peak rose rapidly and declined slowly. The change is attributed to the speed of the meteor shower's drift in relation to Earth's orbit.

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Sky & Telescope magazine
Space Weather

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