Glossary of Meteor Terms 
 

The following glossary defines (somewhat loosely) the terms associated with meteor science. Detailed definitions are not provided, and those given are defined in a sense pertaining to meteor astronomy.
 

Absolute Magnitude:    The stellar magnitude any meteor would have if placed in the observers zenith at a height of 100 kms.

Bolide:   A bright exploding meteor.

Burst:   A sudden increase in brightness along the path of a meteor.

Fireball:   Bright meteor, arbitrarily defined as exceeding magnitude -4.

Flare:   Alternative to burst, meaning a sudden increase in meteor brightness.

Geocentric:   Earth centered

Heliocentric:   Sun centered

Inclination:   In the solar system, the angle between an orbit and the plain of the Earth’s orbit (ecliptic)

Ionisation:   The addition or removal of electrons to/from an atom. For a meteor entering the earth's atmosphere, the friction of entry may induce the ionisation of surrounding atmospheric gases, resulting in a visible glowing train.

Maximum:   The date of peak activity of a meteor shower. Often quoted in stream lists.

Meteor:   A particle which passes through the atmosphere and which, because of friction, burns up and produces a bright path across the sky. Also commonly known as a "shooting star".

Meteor Stream:    A number of meteors with approximately parallel trajectories. The meteors belonging to one shower appear to emenate from their radiant. See ‘Stream’ and ‘Shower’

Meteorite:   A meteor which survives passage through the atmosphere to reach the Earth's surface. Successor to a meteor.

Meteoroid:   A small solid particle in space. Precursor to a meteor.

Micrometeorite:   A small particle which remains unaffected by passing through the Earth's atmosphere.

Observed Hourly Rate:    The rate of meteor activity for a meteor radiant when it is situated on the observer's meridian. Often quoted in Stream Lists, and serves as a guide to the relative activity of a particular stream.

Path:   The projection of the line of motion of the meteor on the celestial sphere, as seen by the observer.

Photographic Observations:    These meteors are captured on a photographic film or plate. The accuracy of the derived meteor coordinates is very high. Normal lens photography is restricted to meteors brighter than about +1. Multiple station photography allows the determination of precise meteoroid orbits.

Poynting-Robertson effect:    A dissipative force due to the anisotropic loss of momentum by a particle through re-radiation of solar energy.  This causes aphelion collapse such that a circular orbit is soon attained; thereafter the particle spirals slowly towards the Sun.  Small particles (below 1cm) are most severely affected because the force
caries as the reciprocal of its size.

Radiant:   A direction in the sky from which, by perspective, meteors appear to come if they share a common orbit.

Semimajor Axis:    Half the length of the major axis of an ellipse, a standard element used to describe an elliptical orbit.

Shower:   Meteors active over a defined period of time and belonging to the same radiant are defined as shower meteors. Shower meteors enhance the meteor activity over and above that of the normal sporadic meteors.

Sporadic:   A meteor not belonging to a defined stream.

Storm:   A period of very high meteor activity.

Stream:   A group of meteors having similar orbits.

Telescopic Meteors:    Meteors witnessed with optical aid.

Trail:   A short term train, the bright streak across the sky left by a meteor.

Train:   Glowing column of light produced as a meteor ionises the surrounding air as it enters the atmosphere. Trains may last for half a minute or much more. As opposed to a trail or wake, a train persists after the bright streak of the meteor vanishes. A train appears either as a bright or dark streak left after the bright streak of the meteor path across the sky vanishes.

Universal Time:   The local mean time of the prime meridian. It is the same as Greenwich mean time,
 counted from 0 hour beginning at Greenwich mean midnight.

Wake:   Alternative name for a trail.

Zenithal Hourly Rate:   The theoretical rate of observed meteors for an observer viewing a meteor radiant at the zenith, under skies limited by magnitude 6.5. Often quoted in stream lists and used as a relative guide to stream activity.

 


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