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Re: (meteorobs) Very Fast Sporadics
In a message dated 98-09-16 12:16:06 EDT, you write:
Lew>>Of course you can always make your own judgement calls, George - though
when
your plots are recorded by IMO, there's really no judgement call is there?
Either they match objective criteria for a shower or they don't?<<
You are mostly right...but there is still some judgement calling by the
observer. Such as estimating speed or meteor duration, distance traveled,
Confidence in the accuracy of the plot, how far away the meteor is to a
radiant which all goes into the plot and recorded by IMO. If I saw a meteor
that was about 8 degrees long and 20 degrees from a radiant and gave a it a
confidence plot accuracy of 1 and it happened to have the appropriate speed
for the radiant...but missed the radiant by 10 degrees....I wouldn't include
it as a shower member. It appears that the actual size of most meteor shower
radiants aren't very big...usually about 1 or 2 degrees in diameter.
Lew>>Think about it: if we relied on your interpretation of your plots to say
those
meteors were *not* DAUs, wouldn't we have to agree with George Gliba (or
anyone
else for that matter) if they interpreted their plots to mean there *were*
DAUs
on a given night, or Aries Triangulids, or Upsilon Pegasids, or Andromedids,
or
anything else for that matter??? Can't have it both ways...<<
Not all meteors belonging to a shower are going to line up with the radiant
for an observer. Hopefully with experience there will be less of these or at
least closer alignments. Or at least record the accuracy of one's plot as
honestly as possible. If you got a good look at the meteor and have the
privilege of it leaving a train to help with the alignment and perhaps a long
alignment tool (such as the two foot long cord I use) then these will be a 1
in accuracy. If I saw a meteor out the corner of my eye and had to turn to get
a look about the time it disappears...I would give it an accuracy of 2. And if
I got an impression that a meteor traveled off in a certain direction, but
didn't really know roughly where it lined up with the stars, I give these a 3.
The 3's are mostly to indicate that I saw a meteor heading a certain direction
in a generalized area. If I can't even get that...I don't plot it and simply
call it a sporadic. This usually happens when I see multiple meteors nearly
the same time or when I'm in the process of getting an alignment or plotting
and writing info down.
As for agreeing with Gliba for an interpretation of his results depends on the
reality of the shower in question. If he's claiming activity for a shower that
is a bonafide shower and most experienced observers are getting something
similar then it's believable. But if he is repeatedly claiming activity for a
shower that apparently has less rates than can be reasonably picked out from
the sporadic background and hardly anyone else is seeing it too, then it
becomes less believable. If an observer reports enough of these that can't be
verified by other observers, his interpretations of a shower might be of
suspect?
Lew>>Anyway, based on your assertion that ALL FIVE meteors appeared to
radiate from
"The Kids" (again 10o degrees from the DAU radiant), and that the DAU radiant
is probably relatively ill-defined even assuming it IS a single radiant, and
that even a well-defined radiant can (according to the IMO method) have
meteors
TWENTY OR MORE degrees in error assigned to it if they're sufficiently far
from
the radiant (of course you are familiar with that part of IMO's reduction
method)... Again, if we assume all this, it seems to point mighty heavily to
an
objective assignment of these meteors as DAUs. <<
For three of the meteors in question I agree...if the plots are sufficiently
far from the radiant area, but due to the trains giving me a very good
alignment for the other two I think it would be wrong to include them with the
DAU's. I will be listing at least those two as sporadics when I make up my
report.
Lew>>Judgement calls, committee
votes, or personal views aren't at issue, are they?<<
On those two I made a judgement call. Depending on how far away I plotted the
other three I will be making judgement calls on what I will designate them
also.
Whether I was accurate on my alignment or not doesn't matter...the fact still
stands that 5 ended up by chance in the kids...even if 3 ends up being called
DAU's. I do not consciously make an effort to make my plots align up with any
known or unknown radiant.
Lew>>Of course, I haven't seen your plots! It could be two of those meteors
were too
long to be DAUs, but weren't too long to match an apparent Kids radiant 10
degrees away... <<
One is too long...the one that passed thru the DAU radiant itself and left the
train. The other is sufficiently long enough to be coming from a radiant at
either place. But the two second train seems like an eternity when you have an
alignment cord in your hands. My eyes have already been drawn to this location
when the meteor appeared. The train simply made it very easy to make a good
alignment...Plenty of time to tweak the cord to satisfaction and see where it
lines up with.
Lew>>(BTW, isn't putting "radiant" in quotes spurious? You can argue
that every meteor actually DOES have a radiant, whether it's a shower meteor
or
not! Find the point of tangency of a meteor's orbit with our globe, and
project
that norm into space: there's your radiant.)<<
When I talk about radiant I'm assuming that there is an active point that
multiple meteors seem to come or radiate from. Obviously every meteor has a
trajectory and a point that it seemingly came from. But not every meteor will
have an apparent association with others in speed and the same radiant point.
I indicate radiant with the quotation marks to indicate that I'm assuming for
the sake of discussion that there is a radiant where multiple meteors are
related. When I'm talking about a fake or non established radiant, I use the
quotation marks to indicate this. If we are talking about a real or
established shower radiant, I will leave the quotation marks off.
George Zay