ABSOLUTE BEGINNERS
This article was updated in
the November 2006 Beginners Magazine
METEORS
There
are two types of Meteor, the first are thought to originate
from the large lumps of rock left over when the planets formed,
known as ASTEROIDS which orbit the Sun between Mars and Jupiter.
Very rarely two Asteroids collide but when they do, chips
of Rock and Iron are thrown off and occasionally head towards
Earth. These may be a few millimetres across or up to tens
or even hundreds of metres across. They are quite rare and
are seen as individual 'fireballs' sometimes impacting the
ground as METEORITES and if big enough may even cause craters.
The second type originate from comets and are much more common.
As a comet, which can be thought of as a giant dirty snowball,
approaches the Sun, the frozen gases and water boil off and
are blown away by the radiation from the Sun. Dust particles
released by the melt are heavier and therefore continue more
or less on the same orbit. These particles spread out along
the orbit path and may eventually form a complete ring around
the orbit. Once a year the earth may pass through this stream
of particles which enter the atmosphere as Meteors. Travelling
at between 11 and 76 kilometres per second they burn up in
the thin atmosphere at a height of about 100 kilometres.
Different
particle streams may be inclined at different angles to the
Earth's orbit therefore meteors can enter the atmosphere at
almost any angle but each stream always appears to radiate
from the same area of the sky each year. The shower on the
end of October will appear to radiate from the constellation
of Orion that is why it is called the Orionids. See the chart
below. Orionid meteors are associated with Haley's Comet.
Meteor showers occur at the same time each year and appear
to radiate from the same point in the sky each year so each
shower is named after the constellation in which the radiant
point is located. No equipment is needed to observe meteors
just sit in a reclining chair or lay on the ground and look
up. On any night there will be a few stray meteors called
sporadic meteors but during showers there may be one or more
every minute. The shower usually lasts from a few days to
a couple of weeks, often with an extra peak in the middle
of the period. The following table lists the main meteor showers
and the date of the peak.
THE MAIN METEOR SHOWERS
PERIOD SHOWER NAME MAXIMUM
Jan 1 - 4
Quadrantids Jan 3
April
10 - 22 Lyrids April
2
May
1 - 8 Eta
Aquarids May
4
June
17 - 26 Ophiuchids June 19
July
15 - Aug 15 Delta
Aquarids July
27
July
15 - Aug 25 Capricornids Aug 2
Oct
15 - 25 Orionids Oct 21
Oct
26 - Nov 16 Taurids Nov
3
Nov 15 - 19
Leonids Nov 18
Dec
9 - 14 Geminids Dec13
Dec
17 - 24 Ursids Dec
23
OBSERVING METEORS
Before
rushing out into the garden to look for meteors, there are
a couple of things to consider for your own comfort, the first
a most important is clothing. The nights at the end of October
can be cold so it is essential to dress in warm clothes. A
number of layers of clothes is often better than one overcoat
so a vest or tee shirt, a second long sleeved shirt, one or
two jumpers, perhaps a body warmer and then an outer jacket.
Wax jackets are cheap and are good for keeping the damp out
if you will be observing from a position on grass. Two or
three layers on the legs are also necessary. Long leg thermal
pants are excellent for men or women although tights will
do but it must be said, tights look better on women. Track
suit bottoms are also good as an under garment. Then jeans
or a thick pair of trousers should be worn over the top. Water
proof trousers are also good for keeping the damp and wind
out. Two pairs of socks are a good idea and warm shoes, most
trainers these days are padded and are quite warm. A woolly
or padded hat is essential because up to 20% of the heat of
the body is lost from the head but peaked hats should be avoided.
Finally a pair of gloves must be worn. It is always best to
start warm and stay warm because once the cold has set in
it is very difficult to get warm again.
A garden
chair is an excellent piece of equipment especially the type
that can be reclined into a near laying position. This will
help avoid neck and back ache when looking up. When sitting
in a garden chair a blanket or old quilt can be used for additional
warmth. A sky chart will be useful to locate the part of the
sky where the meteor has been seen. To read the star chart
in a dark garden will require a torch but a bright white light
should be avoided. A red lamp such as a rear cycle lamp is
better, to avoid ruining the dark adaptation of the eyes.
Even this may prove too bright so adhesive tape and card can
be used to shutter off some of the light, a 10mm hole in a
card black out should provide enough light.
You
may wish to take notes of what you have seen or even mark
the positions of the meteors on your star chart so a pencil
should be taken out to the observing spot. If you intend to
have a long observing session, especially for a meteor watch,
then a hot drink in a flask would avoid missing some of the
show and avoid losing dark adaptation by going indoors to
make a hot drink.
Most
of all, ensure that you are comfortable before you start observing
and have everything you need to hand. It is very irritating
to have to keep getting up and try to find something you have
forgotten, especially if you need to go indoors to get it.
Once you are comfortable and settled, with everything you
need, then you are ready to start the meteor watch session.
Now
on to
where to position yourself. Use the patio or path if possible,
they are more comfortable and less prone to dampness from
dew. Obviously try to set up away from trees or buildings
but this may not be possible so set up in the best place to
view your intended target, you can always move to another
position later. Make sure you have everything to hand, a small
table or box by your side, will provide a convenient place
to put your chart, torch, spectacles or even a hot drink and
will save fumbling around on the ground for things.
To
start viewing allow about five minutes for your eyes to get
used to the dark. This period can be used to familiarise yourself
with the sky and work out where everything is. Try to turn
off all lights around you. If there is a street light bothering
you, it may be possible to erect a screen around yourself
using garden canes, step ladders, washing poles, string and
old sheets, curtains, towels or even news papers. Even lights
which appeared dim, when you first began your session, seem
to get very bright when your eyes are fully adjusted to the
dark.
It
is useful if you can observe from your own back garden because
you can quickly get used to the positions of stars from one
night to the next. It is not always possible to use your own
garden due to dazzling effect of street lights or perhaps
trees or buildings blocking the view. It may be necessary
therefore to go to a darker area away from lights. If this
is the case it is much better to go with a friend, if possible,
as it will be safer and more enjoyable. A remote observing
site also has the disadvantage of having to transport any
equipment. If it is decided to try a remote site always check
the weather forecast first this might save a lot of travelling
and anguish when the sky clouds over shortly after all has
been set up.
After
making yourself warm and comfortable and allowing enough time
for your eyes to become adapted to the dark it is time to
start observing. The first thing to do is to look around the
sky to find a familiar object, the most common thing used
is the constellation of Ursa Major also called the Plough,
The Great Bear or to the Americans The Big Dipper. This is
probably the best known of all the constellations and is always
somewhere in the sky from northern latitudes.
When
Ursa Major has been found there are two further steps to take.
First find Ursa Major on your star chart, remembering to only
use a dimmed red lamp. Next look again at Ursa Major in the
sky and satisfy yourself that you can identify the 'saucepan'
shape. Then locate the two stars forming the side of the pan
furthest from the handle. Follow an imaginary line upwards
from the two stars, away from the saucepan. About six times
the distance between the two stars away from them, there is
a lone star in an area with no other bright stars, this is
Polaris, the North Star. If you face the direction of Polaris
(it is not directly above) this is north. Turn completely
around and you will be facing south. When facing south, west
is to your right and east to the left. Now position your star
chart just above your eyes ensuring that the south position
marked on the map is at the bottom. What you see on the chart
should be what you see in the sky. Normally the centre of
the chart is the position directly above the ZENITH.
THE ORIONIDS
OCTOBER 15th - 25th
Orion
will be rising over the eastern horizon at about 11 o'clock
so will not be fully visible until about 1 o'clock in the
morning. The position where the Orionid meteors appear to
originate, the radiant, is above and to the left of Orion's
left shoulder. You will not need to use binoculars and a telescope
will be useless for observing meteors. They are best observed
with the naked eye. Position your chair so you can see the
sky from the eastern horizon to almost directly above. The
Orionids should appear to radiate up from the horizon. You
can start before midnight but there will most likely be less
meteors at this time. There are two reasons for this, first
the radiant is below the horizon so fewer meteors will appear
above the horizon and secondly after midnight Earth will be
ploughing head on into the main meteor stream. It will be
useful to familiarise yourself with the positions of the constellations
in the direction you are looking. There will be plenty of
time to do this while you are waiting for the meteors. You
can then use the constellations to record the track of the
meteors as they speed across the sky.
If
you feel quite enthusiastic about observing the meteors, you
may wish to make a log of every one you see, this can be done
in two ways. Notes can be made on a pad, detailing the time,
and direction and brightness. If will be necessary to note
which constellations the meteor passes through or at least
where it ended. These notes can then be plotted on to the
chart later. You could alternatively draw the path on your
chart and note the time and brightness on the line. The second
should be more fun because if the shower is good you will
soon see a pattern develop where the lines trace back to a
common point in Orion. There may also be some sporadic meteors
which do not originate in Orion these are also interesting
when marked on the chart. Here is an example of how the chart
might look, note the sparodic meteor marked in blue.
THE SKY AS IT APPEARS
AT 12:00 ON THE NIGHTS OF OCTOBER 21st AND 22nd
(The paths of Orionid
meteors are shown drawn on the chart)
The
Orionids tend to be very fast meteors because they hit the
atmosphere head on combining the speed of Earth (61000mph)
with the meteor (perhaps 50000mph) to make a combined speed
of 111,000mph. Some brighter meteors may leave a persistent
trail in the sky for up to 5 seconds after the meteor has
gone.
The
clarity of the sky will make a significant difference to the
number of meteors that can be seen. Any mist or hazy cloud
will severely reduce the chance of seeing the fainter meteors
especially if observing from a light polluted area. If it
is clouded there is of course no chance of seeing any meteors
at all. It is never possible to predict when the maximum peak
might appear and sometimes it may not appear at all. This
it because the dust from the comet that produces the meteors
moves through space in wisps and filaments so all depends
on whether Earth passes through a filament and how thick that
filament is. The only thing that is predictable about meteor
showers is they will always be unpredictable.
Just
hope for clear skies and a good meteor shower.
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