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Re: Estimating Velocities
Estimating Velocities,
After reading some responses to my question about "are estimated Meteor
Velocities used for anything other than shower association?", I feel
comfortable about the NAMN 0-5 scale. As Mark explained, to teach a new
observer "fresh from the Cabbage Patch" on how to make velocity estimates for
the sole purpose of shower association, it would be easier to have a simple
scale without all the mental gymnastics. I was with Bob when we observed the
1994 Alpha Aurigid outburst. The meteors were long and lasted about 2
seconds. Using the NAMN scale, I would give those nothing less than a 3. A
one would have taken about 15 seconds or more to accomplish. The scheme of
the NAMN scale is to allow a judgement on the odds of any meteor being a
shower member. The Alpha Aurigids for example, with a velocity of 66 km/s is
assumed a NAMN value of 5 for it's fastest expected possible appearance.
With velocities appearing to be slower as it originates near the radiant or
with a lower radiant elevation, I'd expect it to have a range of velocities
appearing somewhere between 3-5. As you know, velocity alone doesn't signify
a shower member. If I'm plotting or I note the alignment to come from the A.
Aurigid radiant, I'd then note what velocity scale number I gave it. If it
fell in the 3-5 range, the odds of it being an A. Auriga are quite high and I
note this. If the alignment was good and I got a 1 or 2, it immediately
becomes something else and most likely a sporadic. Another example would be
the Alpha Capricorns. It's listed velocity is 25 km/s. Using the NAMN
scale, it would be assigned a 2 for it's fastest appearance. Now again, if I
plotted or noted a meteor that aligned with the A. Cap radiant and assigned a
scale number of 1,2, or 3...I'd count it as an A. Cap. But if the scale
number I gave it was a 4 or 5..dot it immediately becomes something other than a
A. Cap. One more example...the Geminids . Its listed velocity is 35 km/s.
This would have a scale number of 3 for it's fastest appearance. If I
assigned a properly aligned meteor a scale number of 2, 3, or 4, it would be
designated a Geminid. but if the scale number got a 1 or a 5..dot it again
becomes something else.
Knocking one's self out on a deg/sec accuracy is fine and dandy, but it's
accuracy will never be good enough to determine anything other than shower
associations either. Definitely not good enough for orbits. The scale works
just as good as deg/ sec, but I believe it's much simpler for the purpose
used for. I find it cutting it kinda close to estimate sudden appearing
durations for 1/5 second. But an experience observer should be able to at
least look at any meteor and judge whether it appeared Very Fast, Medium or
Very Slow. And in short order, a new observer can make these kind of
judgements as well with a lot less frustration. There is no need making
various data gathering factors more complicated than what they will
ultimately can be used for. I'm not against anybody using Deg/sec if they
enjoy the mental exercises, but you must remember that it's whole purpose is
for shower associations. Neither method is accurate enough to do much
else...this is where various photography methods come into play.
George Zay