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(meteorobs) Meteor related terms



The exact terminology of meteor astronomy was set up in 1961 by the IAU. Here is
the list of terms with their appropriate meanings. I hope you find it useful.

Rainer
---------------------------------------------------------------
Rainer Arlt -- Visual Commission Director
International Meteor Organization
100114.1361@compuserve.com
Home page of IMO: http://www.imodot net
---------------------------------------------------------------

Definition of terms by the IAU Commission 22, 1961.

A. meteor:     in particular, the light phenomenon which results from the
               entry into the Earth's atmosphere of a solid particle from
               space; more generally, as a noun or an adjective, any
               physical object or phenomenon associated with such an event.
B. meteoroid:  a solid object moving in interplanetary space, of a size
               considerably smaller than an asteroid and considerably
               larger than an atom or molecule.
C. meteorite:  any object defined under B which has reached the surface of
               the Earth without being completely vaporized.
D. meteoric:   the adjectival form pertaining to definitions A and B.
E. meteoritic: the adjectival form pertaining to definition C.
F. fireball:   a bright meteor with luminosity which equals or exceeds that
               of the brightest planets.
G. micrometeorite: a very small meteorite or meteoritic particle with a 
               diameter in general less than a millimeter.
H. dust:       when used with D or E---finely divided solid matter, with
               particle sizes in general smaller than micrometeorites.
I. absolute magnitude: the stellar magnitude any meteor would have if
               placed in the observer's zenith at a height of 100 km.
K. trajectory: the line of motion of the meteor relative to the Erath,
               considered in three dimensions.
L. path:       the projection of the trajectory on the celestial sphere, as
               seen by the observer.
M. train:      anything (such as light or ionization) left along the
               trajectory of the meteor after the head of the meteor has
               passed.
N. persistent: an adjectival form for use with M indicating durations of
               some appreciable length.
O. wake:       train phenomenon of very short duration, in general much
               less than a second.
P. radiant:    the point where the backward projection of the meteor
               trajectory intersects the celestial sphere.
Q. earth-point:the point where the forward, straight line projection of the
               meteor trajectory intersects the surface of the Earth.
R. zenith attraction: the effect of the Earth's gravity on a meteoric body
               increasing the velocity and moving the radiant towards the
               zenith.
S. orbit:      the line of motion of a meteoric body when plotted with
               reference to the Sun as origin of co-ordinates.
T. shower:     for use with A or D---a number of meteors with approximately
               parallel trajectories.
U. stream:     for use with A or D---a group of meteoric bodies with nearly
               identical orbits.

When the words visual, photographic, telescopic, radio, photo-electric are
combined with A they should indicate only the method of observation, and 
should not be used as an indication of brightness or size. For the latter
parameters it is recommended that simple words be used such as bright,
faint, large, small, etc.


Recommended symbols for velocities:

V_a (instrumental velocity)   the uncorrected velocity as recorded by an 
                              instrument.
V_0 (observed velocity)       V_a corrected for instrumental errors of all 
                              types.
V_\infty (no-atmosphere vel.) V_0 corrected for deceleration in the Earth's
                              atmosphere.
V_g (geocentric velocity)     V_\infty corrected for rotation of the Earth,
                              and the gravitational force (zenith
                              attraction) of the Earth.
V_h (heliocentric velocity)   V_g combined with the vector of the Earth's
                              motion around the Sun to give the motion of
                              the meteoric particle relative to the Sun.