The Geminids Are Back

Event Summary

Join us at the Prairie Heritage Center Thursday, December 13, 2012 at 6:30 P.M. for a dark walk on the prairie – on foot or snowshoe – weather dependent.

The cold nights of December are a reminder of many things, such as festive holidays, food, and desserts. But if you look to the sky for several days before and after the night of December 13/14, you are likely to discover something more.

December is the month of one of the best meteor showers of the year. Known as the Geminid meteor shower, it gets its name because the meteors seem to originate from the constellation Gemini. The Geminids are also one of the strangest meteor showers for a couple of reasons.

First, several of the major meteor showers that are visible every year are recorded in historical texts that date back a thousand years or more. But the Geminids were only first recognized during December 1862. In fact, the Geminids went from a barely noticeably meteor display to a spectacular meteor shower in about a century. Since the hourly rates have remained fairly stable since the 1970s, astronomers believe they will soon start declining and that the Geminids will hardly be detectable by the end of this century.

Second, the parent object of the Geminids, known as Phaethon, is very mysterious because it is not a comet, but a minor planet. Most of the major meteor showers have well known comets associated with them and these comets help to replenish the meteors as they shed their dust and gas when close to the sun. There is no evidence that minor planets shed any of their material, so the actual replenishment of dust in the orbit of the Geminid meteor stream has been a mystery.

For the most part, astronomers have believed that Phaethon was probably an extinct comet. Its orbit takes it very close to the sun and the heat would likely have caused it to lose all of its dust and ice in just a century or two. But there is a curious consistency to the annual Geminid display that could only be explained by assuming something was still dumping dust into its orbit. A paper published two months ago may finally explain what is going on.

David Jewitt and Jing Li picked up on an alert that Phaethon was going to pass through the field of the STEREO-A spacecraft that constantly monitors the sun. The event was to occur during the period of June 17-22, 2009. As they studied the images of the minor planet moving through the spacecraft's field of view, they noted an unexpected brightening, which was due to dust being released. They noted that Phaethon was "too hot for water ice to survive, rendering unlikely the possibility that dust is ejected" in the same fashion as a comet. They concluded that the dust was released as a result of the sun cooking the minor planet, which caused rock on the surface to fracture. If just ten such events occurred each time Phaethon passed close to the sun, enough dust would be released to sustain the Geminids. Further observations will be needed to determine if this was a one-time event or not, but, for now, this is the best theory to explain what keeps the Geminids going.

The Geminid meteor shower produces hourly rates of 70-80 and appears to radiant from the northern portion of the constellation Gemini. Unlike most of the other major showers, the Geminids can be seen throughout the night, although the hourly rates really pick up after 9:00 p.m. This is not a perfect year for the Geminids, as the moon will be in the sky until early morning hours; however, the Geminids typically produce a lot of bright meteors, so moonlight can not totally block the display. Get a reclining lawn chair, lie flat so that you are gazing straight up into the sky, and remember to dress warmly!

Above information from: http://www.examiner.com/article/the-geminids-are-back

For more info: Check out Gary W. Kronk's article on the Meteor Showers Online web page at http://meteorshowersonline.com/geminids.html

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