Royal Astronomical Society of New Zealand The Geminid Meteor Shower in December

Chart showing the sky surrounding the radiant of the Geminids.

The Geminid Meteor shower is one of the most active of the year, sometimes surpassed only by the Perseids in intensity. Although this year, the Leonids will certainly have out-performed them all.

The shower peaks on the morning of 15 December in New Zealand. The Geminids don't seem to have a sharp peak like the Leonids, and observations can be made for a week either side of the peak.

At it's height, the Geminids have a zenith hourly rate of about 80 meteors per hour. So, if for you the radiant was at the zenith, and you could observe the whole sky at once, you might expect to see 80 meteors an hour.

Alas, in New Zealand, the radiant is low. In fact it lies just a degree or two to the left of, and slightly below, Castor. So, in New Zealand we effectivly lose out on seeing 50% of the meteors before we start. But it is still a shower worth looking at. I have found from when I lived in Auckland, and if it was fine, seeing a dozen or more Geminids an hour around the peak was quite normal. And of course one cannot observe all the sky at once. Geminids are inclined to leave good trains, and some of those meteors travel long distances. One I observed appeared first near Sirius, and travelled overhead and a long way towards the southern horizon. Remember, meteors do not appear at the radiant, unless they are heading straight for you, but generally tens of degrees from it.

Best time to look for Geminids is any time after about 1 or 2 am through until dawn. Gemini will be approaching north. I would suggest you look for Geminids streaking through the sky in the region of Orion and the area of sky to the right of Orion. Make sure you have a dark sky from northwest sound to east, and at least up to the zenith. Keep glow from city lights to the south of you.

Most meteor showers are associated with cometary debris travelling in the orbit of the comets. The Geminids are a bit different. The appear to be travelling in the same orbit as Apollo asteroid 3200 Phaethon. Is this an asteroid that perhaps was once surrounded by and icy snowball of cometary matter?

The chart shows a field of view to the north about an and a half before sunrise. From the mid South Island of New Zealand, the other pair of the twins, Pollux (just above Castor) will have an altitude of about 20° and be nearly due north. For observers further north, Pollux will be a little higher.

In 2007 Mars will be 15° from the radiant and close to opposition. The Moon 31% lit, will set soon after midnight so have no effect when the radiant is highest

Chart prepared with the aid of GUIDE 7.0.

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