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- Bolide. A term sometimes used to describe bright meteors
which break up.
- Curved Meteors. Meteors whose paths are not straight. In some
cases it may be that by chance a second meteor
appears at the point where another meteor has
just ended. Other explanations involve the
meteor being a bat or night flying bird
lit up by streetlights. Unfortunately visual
observations of curved paths will always be
suspect: a satellite followed against the star
background will appear to wander slightly from
side to side!
- Dark meteors. These are meteors which appear darker than the
sky background. Although some could be meteoric
in origin, other possible explanations involve
floaters in the eye and unilluminated objects
(e.g. birds, insects) being seen against the
less dark sky background.
- Daylight Showers.These are meteor showers whose radiants are only
above the horizon during the hours of twilight or
daylight and so can only be studied using radio
methods. Several are active during May and June,
including the Omicron Cetids and Beta Taurids.
- Diurnal Variation. This is the tendency for meteor rates from the
sporadic background to be significantly higher
late in the night than early in the night. It is
due to the fact that before midnight an observer
is looking in the direction from which the Earth
is travelling (and so some meteors are being
left behind) whereas after midnight the
observer is on the side of the Earth facing the
direction of travel (and the Earth is 93catching
up94 with some meteors).
- Fireball. Although occasionally used for any meteor of
negative magnitude, this term is usually reserved
for much brighter meteors. The International
Meteor Organisation defines fireballs as being
meteors of magnitude -3 or brighter. The meteor
section of the British Astronomical Association
on the other hand has a much stricter definition,
requiring the meteor to be magnitude -5 or
- Flare. The sudden brightening of a meteor, most commonly
near the end of its path when it is referred to
as a Terminal Flare.
- Limiting Magnitude. A measure of the darkness of the sky during a
meteor watch. It is defined as the magnitude of
the faintest star visible in the area of sky
- Meteor Storm. The rare occasion (a few times per century) when
the sky is filled with meteors. It is usually
defined as when the meteor rate exceeds 1000 per
- Minor Shower. These are the lower activity - usually defined as
ZHR less than 10 - meteor showers. Unfortunately they can
be difficult to identify reliably using visual
methods and consequently lists of minor showers
are usually littered with many spurious showers.
- Nebulous Meteor. Meteors that appear nebulous rather than being
sharply-defined are occasionally reported.
Various explanations have been suggested, ranging
from very fragmentary meteors, through night
flying birds and bats, to ball lightning.
- Path. This is the route of the meteor through the
atmosphere when projected against the star
background. (cf trajectory)
- Poynting-Robertson Effect. This is an effect of solar radiation which
affects low mass particles more than
higher mass particles. It changes the
orbits of the particles slightly. A result
of this is seen in some showers for which
the peak rates of faint (low mass) meteors
occur earlier than the peak rates of
- Radiant. This is the area of sky from which the meteors
of a particular meteor shower, when their paths
are projected backwards, appear to have radiated.
It marks the direction in space from which the
meteor stream is approaching the Earth. Although
meteor shower lists often give the impression
that the radiant is a point in the sky, it is in
practice an area of sky a few degrees across.
- Seasonal Variation. This is the tendency for sporadic meteor rates to
be significantly higher in the autumn than in the
spring for northern hemisphere observers (and the
reverse for southern hemisphere observers). The
reason is that the direction in which the Earth
is travelling is higher in the sky in the autumn
than in the spring (e.g. Gemini in September
Sagittarius in March).
- Sounds. Sonic effects are sometimes reported from bright
fireballs minutes after the visual sighting.
However, some observers sometimes report sounds
from more ordinary meteors simultaneous with the
appearance of the meteor. Descriptions include
swishing sounds, cracks, hissing.
Although some observers believe the sounds to be
genuine, possibly involving some (unspecified!)
part of the electromagnetic spectrum, the
prevailing view is that the sounds reported are
purely psychological - an analogy with fireworks.
- Sporadic Meteor This is a meteor which does not belong to a
meteor shower. In practice, the sporadic meteor
background will include meteors from unidentified
- Spurious Meteors. These are objects seen during meteor watches
that appear similar to meteors but aren't.
Examples include flashing satellites and planes,
twinkling bright stars near the edge of the field
of view and birds illuminated by streetlights.
Other cases may be due to flashes of light
within the eye-brain system.
- Spurious Showers. If the paths of two meteors are projected
backwards there is a 50% chance that they will
intersect somewhere in the sky. By chance, other
the paths of other unrelated meteors may also
project back into this area of sky and the
discovery of a new meteor shower is claimed.
The higher the sporadic rates, the greater the
likelihood that such chance lining-ups will
occur and a few misidentified major shower
meteors can also be included.
- Stationary Meteor. A meteor that is travelling head-on towards the
observer and thus appears as a flash of light at
a point in the sky.
- Trail. An ambiguous term - it is better to use either
path or train.
- Train. The ionised dust and gas along the path of the
meteor which remains visible for a number of
seconds after the meteor has passed.
- Trajectory. This is the actual route of the meteor through
the atmosphere. (cf path)
- Wake. A meteor train that is so short lived that it
appears to move along with the meteor.
- ZHR The Zenithal Hourly Rate of a meteor shower is
the number of meteors from that shower that a
single observer with an unobstructed view would
see in one hour if the meteor shower radiant was
directly overhead and the Limiting Magnitude was
6.5. Under less favourable observing conditions,
the number of shower meteors seen is likely to be