THE SKY GUIDE CHALLENGE
Can you spot and record a meteor train, which lingers after its trail has faded
August is great for meteors.
Given clear skies, a favourable
Perseid maximum will provide
many trails with other active
showers adding to the mix too.
This month’s challenge is to
try and record a phenomenon
often seen following a bright
meteor, a glowing entity
known as a meteor train.
A meteor trail represents
the death throes of a typically
small rock or meteoroid
ablating in our atmosphere.
Often incorrectly described as
burning, the actual process is
width and several tens of
kilometres in length.
A larger particle, say the size
of a grape or perhaps a golf
ball, produces a brighter trail.
It may also cause enough
ionisation for the column of
glowing atoms to persist for
some time after the trail has
faded, and this is known as a
meteor train.
The longevity of a train,
typically just a few seconds,
is related to the brightness
of the trail, brighter trails
producing more persistentAugust 2021 BBC Sky at Night Magazine 55more complex. As the
meteoroid enters our
atmosphere it compresses air
ahead of it which generates
KHDW7KHKHDWLVVXIƅFLHQWWR
vaporise the forward face of
the meteoroid. Liberated
atoms interact with
atmospheric atoms raising
their energy state. A short
time later, the excited atoms
return to their ground state,
releasing the energy given to
them as visible light. This is
what forms the trail, a line of
light typically a metre or so intrains. An important
observation is to estimate the
brightness of a meteor trail
and record the length of the
resultant train in seconds.
If you have enough data, this
can be used to predict the
persistence length of a train
for a given brightness of trail.
Trail brightness can be
recorded visually, but
photographically it’s
necessary to tie up a visual
estimate with a known
photographic trail. In this way
it is possible to roughly
calibrate your camera so you
can estimate visual trail
brightness from a
photographed trail.
The longer a train is visible,
the greater the chances it will
distort due to high-altitude
atmospheric winds. For meteor
imaging, keeping exposures
reasonably short, say to 20–30
seconds, may allow you to
record and animate these
distortions over time. It’s also
worth noting that this length
of exposure will allow you to
record a train for longer than
would be the case visually.
Photographic trains have
longer persistence due to
greater camera sensitivity.
If you manage to
SKRWRJUDSKDEULJKWWUDLOƆLFN
from the trail image through
the few that follow it to see
whether a train has recorded
too. Animating these images
will allow the movement of the
ionised gases in the train to
become quite obvious.< Capture a meteor train on
a camera and you’ll record it for
longer than you can visually.
To do so, keep your exposures
short at 20-30 seconds