(meteorobs) Size of radiants.

[Rainer Arlt]

> Thank you Marco, Roberto and Al for your replies. Actually you answered 
> the question as I asked it, however I asked the wrong question. What I 
> had assumed was that the radiant is not a well defined point but is a 
> circle or ellipse from which the overwhelming majority of the meteors of 
> a particular shower radiate. I intended to ask the question of how large 
> is that circle. I have since assumed that ten degrees would be too large 
> for such a circle, but I would still like to propose the question, how 
> large is are radiants in general?

There are two answers to this question: One is the physical radiant
size resulting from precise video or photographic records. They
are between 1-2 degrees for 'normal' showers like the Perseids.

The other radiant size is the one, a visual observer has to assume
when discriminating shower members. Because of the natural errors
of the visual method, this size has to be larger. If you plot
the meteors seen in a star chart, you will see that you cannot 
get these meteors converge in a 1-degree circle. This is why
something like 10+ deg has to be assumed. For meteors farther
from the radiant, larger sizes (better term 'larger tolerance')
has to be adopted.

The ecliptical showers have a larger variety in orbital elements
and produce larger physical radiant sizes. These add to the
'torelance' which has to be adopted.

Hope this helps, best wishes,
Rainer


-- 
Rainer Arlt  --  Astrophysikalisches Institut Potsdam -- www.aip.de
Visual Commission - International Meteor Organization -- www.imo.net
rarlt at aip.de --  phone: +49-331-7499-354  --  fax: +49-331-7499-526