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(meteorobs) Re: Antihelion Radiant



Geert and All,

I believe "DIV" stands for DIVERSE. This covers all showers reported to the
IMO that is not on their current list.

When the Antihelion radiant lies close to another radiant, it is impossible
to distinguish between the two unless one plots and notes velocity
estimates. In that case it would be wise to assign all meteors to the
established radiant. Adding 1-2 additional shower members per hour usually
does not a problem until you start getting five or more shower members per
hour. This rarely occurs with these minor showers. The only showers possibly
affected by antihelion activity are the South Iota Aquarids and the North
Delta Aquarids.  The Alpha Caps are fairly close, but 15 degrees separation
should be sufficient to distinguish these two sources.

Clear Skies!

Bob Lunsford


----- Original Message ----- 
From: "Geert Barentsen" <geert.barentsen@pandoradot be>
To: <meteorobs@atmob.org>
Sent: Monday, July 21, 2003 3:21 AM
Subject: Re: (meteorobs) Observation 19/07/2003



>* Sagitarrids are "officially" over, but the Antihelion
>radiant remains (or not?), but I don't know what to call
>these meteors, so I'll stick to ANT

If I'm correct, the Antihelion source is somewhere in Capricornus right
now, and produces activity all year! (In fact its rates are considerably
higher from +-July til December. See IMO's visual handbook for more
information and references about this.)

The only guideline I know about the reporting-issue, can be found in
Mr.Lunsford's wonderful meteor outlooks; quote: "It may make sense to list
these meteors as antihelions or 'ANT' but a majority of meteor
organizations prefer that you list them from the constellation in which the
radiant is currently located or the constellation where the shower reaches
maximum activity."

The second way is probably the standard procedure to report any higher
activity coming from a certain area in the sky, not associated with a known
shower. My guess is that these rates are most likely added to the
"SPOR"-value right away, when you submit the data to the IMO visual meteor
database.. However, I see that the vmdb also contains meteors that are
classified as "DIV" (wich is obviously not a standard shower code). Can
anybody tell something more about this?

Btw; what if this interferes with actual meteor showers? You could, for
example, report both alpha-Capricornids and antihelion-meteors as "CAP"?
(Tho accurate plottings may enable you to distinguish both). The same thing
happens in August, when the Antihelion-source comes really (really!) close
to the aquarid-radiants.

I'm sure some people may be disappointed that sporadic sources are not
treated like 'real' showers in the processing, but they are probably just
too big (+20°!!), and not observed widely enough to use visual observations
for reliable statistics. Radio-observations have been used in the past to
determine the positions, structure and relative rates of the sporadic
sources (cf. some articles by Jones&Brown in mid-90's), but many questions
remained. Maybe video-observations can gather accurate trajectories and
rates?

Kind regards,
Geert



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