Geminid meteor shower begins: watch out for fireballs
The mysterious Geminid meteor
shower lights the skies of Earth
between 12 and 16 December and is
visible from almost anywhere on the
planet. This year the peak rate is
estimated to be 100-120 meteors per
hour, rivalling the August Perseids,
which are usually the most
spectacular meteor shower of the
year.
A bright, waning moon will
render some of the fainter meteors
invisible for much of the night, so the
observed rate may be down by half.
Nevertheless, the Geminids can
usually be relied upon to produce a
good supply of bright meteors, called
fireballs.
After moonset, in the hours
before dawn, the visible rate should
climb towards the maximum.
To see the meteors, wait for a
clear night and then find a dark spot,
well away from any lights. Allow
your eyes to become fully accustomed
to the dark. This usually takes around
45 minutes. Then look straight up.
You may want to dust off the
garden recliner and climb into a
sleeping bag because in the northern
hemisphere it is going to get cold.
Even in the southern hemisphere,
things can get chilly in the middle of
the night at this time of year.
The Geminids themselves are
something of a mystery. Meteors are
produced when the Earth ploughs
through a stream of dust in space.
Usually those streams are produced
by comets, where the dust was once in
the tail. The Geminids, however,
come from asteroid 3200 Phaethon,
which was discovered in 1983.
American astronomer Fred
Whipple noticed that the orbit of
Phaethon was almost identical to that
of the Geminid stream. This solved the
mystery of the Geminids' parent body
but sparked another. The Geminid
meteoroid stream is the most massive
of those that create showers each year
at Earth, outweighing others by
factors of five to 500 . Yet Phaethon
itself is no longer producing dust at a
rate capable of feeding the stream.
This hints that the behaviour of
the asteroid has changed with time.
Perhaps an impact caused it to lose
much debris in the past or its regular
close passages to the sun produce
occasional outbursts.
One thing is certain, if Phaethon
doesn't start producing more dust
again, the Geminids will gradually
dwindle as the Earth mops them up.
OK, so it will probably take centuries
to make a noticeable difference, but
it still means that we should make the
most of them while they last.
