Behold, the Geminids are coming
Set the alarm for 2am for yearly meteor shower
On the night of November 1213 1833, people across the US were awakened in the early morning by bright light, shouts, and church bells ringing.
From 3am, the skies lit up with the Great Leonid Meteor Storm during which about 100,000 meteors – then called falling stars – could be seen each hour until dawn.
They fell “as thick as snow”. People prayed and were too frightened to go back indoors. There are dozens of predictable meteor showers each year, but very seldom do they approach the 1833 spectacle.
Last month, I explained that meteors are seen when a small grain of sand or stone orbiting the Sun collides with the Earth and burns up in the atmosphere, creating a streak of light.
On a typical night in a dark site with clear skies, a patient observer can see five to 10 meteors across the whole sky per hour. That’s not so exciting.
But in the major meteor showers each year it is possible to see roughly 100 meteors per hour. That is still one to two per minute, so patience is needed.
One of the best each year is the Geminid Meteor Shower that peaks during the night of December 12-13 this year. It will be best seen from about 2am onwards (so determination is required).
The meteors can be seen all over the sky, but they all streak away from a spot in the constellation Gemini, the twins, Castor and Pollux.
Those two stars will rise at midnight and be best seen to the north from 2am until dawn.
The moon is new then, so the sky will be dark. Find a spot away from lights, make yourself comfortable and look from the north right up across the sky.
You may see one meteor per minute (onC average). The Geminids are famous for bright fireballs, so you may see some good ones. I will be watching under the dark skies in the Amatola Mountains.
Why are there predictable meteor showers? Why do they come from one point in the sky?
Meteors come from comets.
There are trillions of comets orbiting the Sun far out beyond Pluto.
Over hundreds of millions of years, small gravitational tugs from passing stars cause some of them to fall into the inner solar system.
They are made of a mixture of water, ice and rock and are small, with very little gravity.
The most famous one, Halley’s comet, is only 8km across. Its gravity is so small that if you landed on the surface, you would only weigh about 20g!
When a comet comes into the inner solar system, the Sun heats it causing the ice to turn to water vapour that blows off the surface carrying the very light rocks away with it.
The wind from the Sun then blows the vapour and rocks into the famous tail of the comet.
Some comets have passed close to the giant planets Jupiter and Saturn, whose gravity caused them to be captured in orbits around the Sun in the inner solar system. That happened to Halley’s Comet which now orbits the Sun every 76 years. If you missed seeing it in 1986, it will be back in 2061.
The rocks and dust that have been blown off the surface of a comet continue to follow the path of the comet, and some intersect the Earth’s orbit once per year at a particular time.
As the comet debris crashes into our atmosphere, we see a meteor shower with many small particles burning up and streaking across the sky – but always from the same point where the orbits meet.
If you can get yourself out of bed at 2am on December 12, find a dark spot and watch for an hour or two. You may see a lot of meteors and even some of the famous bright Geminid fireballs.