[Prev][Next][Index][Thread]
Re: (meteorobs) Re: Radiant Diameters
About radiant diameters:
We have to distinguish between two radiant diameters. One is the physical
diameter which results from orbital dispersion of the meteoroids and is a
few degrees usually. I quote some values for the median (a measure similar
to a average) of total radiant deviations from L. Kresak, V. Porubcan in
Bull. of the Astron. Institutes of Czechoslovakia Vol. 21, pp. 153-170:
Perseids
--------
Harvard I 1.18deg
Harvard II 1.13
Ondrejov 1.25
Odessa 1.36
Dushanbe 1.26
before max: 1.39
maximum: 1.10
after max: 1.33
total 1.26
Geminids
--------
Harvard I 0.44
Harvard II 0.44
Ondrejov 0.53
Odessa 1.00
Dushanbe 0.44
beore max: 0.56
maximum: 0.37
after max: 0.44
total 0.49
First you find the results of several photographic projects, then the
radiant radius before, at and after the maximum of the shower. Other
showers:
Leonids 0.32deg (9)
Orionids 0.84 (30)
Lyrids 0.25 (7)
Quadrantids 1.13 (16)
Southern delta Aqr 1.41 (28)
Northern delta Aqr 1.62 (8)
Southern Tau 2.20 (46)
Northern Tau 1.94 (25)
(Draconids 0.07 (2))
The numbers in brackets are the numbers of meteors involved.
Now for the other radiant diameter: In order to determine the activity of a
minor shower from visual observations, we face two problems. Out meteor
plots will not be too accurate. Therefore, we cannot adopt the physical
radius of the radiant given above to our shower association. We have to
increase the radiant size to an extent that the typical errors in plotting
meteors are accounted for. Then we face the second problem: The larger we
choose the radiant the more sporadic meteors will be erroneously associated
with the radiant. At a certain optimum radiant diameter, the actual shower
rate will be correctly represented by our shower association. That is, we
have to compensate the loss of a few shower meteors due to occasional
strong plotting errors by a few sporadics which accidentally line up with
the (extended) radiant. This optimum radiant diameter is much larger than
the physical one and has almost no relation to that. Appropriate radiant
diamaters for minor showers are:
Radiant distance Optimum
of the meteor radiant diameter
15deg 14deg
30deg 17deg
50deg 20deg
70deg 23deg
These diameters were derived from the plotting errors of experienced
observers and are based on doubly plotted meteors. The IMO Calendar does
not list the diameters of 5deg anymore, since thy have no practical
meaning. The physical diameter is smaller, and the diameter applicable to
the shower association of visual plots is larger, typically between 15 and
20 deg as listed above.
I hope I started to clarify the mystery of radiant sizes.
Rainer Arlt
---------------------------------
Visual Commission
International Meteor Organization
email: visual@imodot net
Homepage: http://www.imodot net
---------------------------------
Follow-Ups: