What is a Geminid Meteor Shower

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The Geminid meteor shower is a particularly spectacular display that can be seen every December in the night sky. This shower is appropriately named because, although shooting stars can occur throughout the sky, many appear to originate from within the constellation Gemini.  In good conditions some 120 to 160 meteors can be seen per hour.

In December 2012, where the sky was not obscured by cloud, the display was particularly dramatic. Observers were treated to a large number of meteor trails set in a dark sky lit only by a new moon. Observers for NASA consider that the Gemini meteor shower shone brighter than the new moon at Cartersville, Georgia, in the early hours of December 14, 2012, and was the brightest display in four years of observation.

Whereas many meteor showers are associated with the gaseous tails of comets, the source of the Gemini meteor show remains unclear. Observations do not support the comet hypothesis and suggest that the shower may be associated with the breakup of a rocky object.

Unlike many meteor showers which have been seen for millennia - the Perseids were first recorded in 36 AD and the Leonids in 902 AD, for example - the Geminids were first observed in 1862. Moreover, the Geminid displays appear to be getting stronger by the year. The shower is of such intensity that scientists believe that between 5 and 500 times more mass burns in the upper atmosphere compared to other meteor storms. Additionally, meteors within the shower move slowly across the sky.

Some explanation lies in the discovery of a rocky object called 3200 Phaethon by the NASA IRAS satellite in 1983.  3200 Phaethon has a highly elliptic orbit and passes inside the orbit of Mercury every 1.4 years. In such close proximity to the sun, some of the rock is thought to burn off and leave 3200 Phaethon surrounded by a cloud of dust. The Geminid meteor shower is thought to arise when the Earth’s orbit passes through the dust cloud. 3200 Phaethon itself is thought to be a fragment from the disintegration of an asteroid, Pallas.

The 2012 Geminid display adds a peculiarity. On the night of 13 December 2012 it coincided with an additional display caused by the Earth's passing thought the gaseous tail of Comet Wartimes. This comet was first observed in 1948.

Although not yet proven to the satisfaction of scientific enquiry, the circumstances surrounding the formation of the Geminid meteor shower are rare. Asteroid fragments such as 3200 Phaethon that traverse the orbit of Earth could be the final relics of comets that have succumbed to tidal forces and desiccation in the inner solar system.

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