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(meteorobs) Re: FOV of Field definition
Lew and All,
You answered your question perfectly. If one looks directly at the
radiant you can see shower members traveling in all directions. If you
are facing 40 degrees away instead of 360 degree coverage you can only
see shower members leaving the radiant in a window of only 140 degrees
assuming a 100 degree field of view. In simpler terms, picture the
radiant as the face of a clock. By facing 40 degrees to the right of the
radiant you will only see the meteors leaving the radiant between the 1
and 5 o'clock position.
Let me make it perfectly clear that the IMO instructs observers,
especially those new to the field, to look 30-40 degrees from the
radiant. It just bothers me to look this far from the radiant when it is
high in the sky as I feel I am missing too much activity. This is just
my personal feelings. Like Lew said use the method that works well for
you.
I would have to respectfully disagree with Lew that shower association
is easier 40 degrees out. I feel that it is much easier and more
accurate to obtain data (length, duration, angular velocity) with short
meteors compared to long ones. Show me two meteors; one 3 degrees long
and the other 15. Have observers estimate their length. Are they really
going to estimate the length of the longer meteor more accurately?
Remember that 3 degrees is the length of the belt of Orion while 15 is
the length from Rigel to Bellatrix (Gamma Orionis).I would bet that most
people would be a degree or two off on the short meteor but at least 4-5
degrees off on the longer meteor.
I do agree wholeheartily with Lew that when dealing with multiple
radiant it is important to look somewhere between the radiants so that
accurate data can be obtained from both of them.
This issue is not of the utmost importance for major showers as there
will be activity wherever you choose to look. It is though critical to
look directly at a suspected or minor radiant in order to observe or
plot possible shower members from this area.
Best of luck with the Ursids tonight. The weather looks favorable here
in Southern California. I'll post my report as soon as I return home
Friday morning.
Happy Holidays!
Bob Lunsford
Lew Gramer wrote:
>
> This topic of where to put your Center of Field of View (CFV) relative to a
> shower radiant, is one we've been through a couple of times before - as with
> most meteor-related topics, probably, after 4 years and 20,000 emails. :>
>
> Bob Lunsford is of the opinion that facing the radiant maximizes perception
> and (he has recently mentioned) may enhance an observer's ability to do path
> shower association while observing. One reason for improved perception that
> I have heard in the past is the fact that shower meteors will appear slower
> (and maybe somewhat brighter on average?) near the radiant, due to the for-
> shortened appearance of these more "head on" meteors.
>
> I wasn't sure I had understood your point about easier shower association,
> Bob? Is it because watchers will be better able to "triangulate" on the
> radiant point, since they'll get to see meteors trace back to the radiant
> from "360 degrees around"? Maybe you can explain that one in more detail?
>
> In any case, many observers share Bob's point of view. (Pun intended!)
>
> Mark Davis writes in the NAMN Observing Guide, and many observers (like me)
> agree with him that facing 30-40 degrees away from the radiant will actually
> improve perception, as shower meteors will appear longer on average, making
> it easier for the eye to detect them. This is especially true for observers
> with narrower fields of meteor perception (say average DCVs of 20o or less).
>
> Also (I would propose), shower associations will be no less accurate, and
> possibly more so. This is because meteors of longer paths will show up the
> distinctive angular velocities of a particular shower better, relative to
> the sporadic background. Also, the path *length* criterion is much easier
> to apply to a meteor, if it is seen more than 20 degrees from the radiant.
>
> And of course, if you are watching MULTIPLE radiants, then having a leeway
> of 30-40 degrees may allow you to choose your CFV in such a way as to view
> more than one of those radiants to advantage at the same time.
>
> So naturally, many observers agree with Mark's view, as well!
>
> And of course, neither of these two views may be correct for everyone: in
> the past, for example, I have suggested to Bob that his meteor perception
> may actually be different from mine, in that he may be most apt to notice
> any *brightening* in the sky, whereas I'm more apt to pick up *motion*.
>
> So the final answer seems to be, "Choose whichever CFV is most comfortable,
> so long as you can see the radiant points of all the showers you're logging,
> well enough to do accurate shower associations". And of course, be sure to
> log your CFV carefully. Then maybe some day, someone can actually analyze
> the global meteor database to find a better answer to this very question! :)
>
> Clear skies!
> Lew Gramer
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