(meteorobs) Nice variety of Fireballs occured.

[Kai Gauer]

On 10/6/07, Ed Majden <epmajden at shaw.ca> wrote:
>
> On 6-Oct-07, at 3:12 PM, meteoreye at comcast.net wrote:
>
> > Thanx, Ed. I didn't know that the AMS had a reference for their
> > definition.
> > It's still a bit imprecise, but would suggest -4 or -5 as a cutoff.
> >
> > Appreciate you help.
> >
> > Wayne

Is it best to try & estimate the brightness of a bolide / meteor as
though it had a 0+ Degree diameter point-source? Or is it better to
"sum" across the average of the entire region? One of the reasons of
why somethings such as the Moon, Venus, Mars & other planets, the Sun,
comets etc appear to be bright is that they are not point-sources (the
planets being generally well-defined disc-shaped objects, comets &
(some) meteors generally looking either like faint fuzzies or with
some degree of tail, & other objects as being clearly non-zero area of
a luminosity source - except (many) stars) - a camera chip might call
this its saturation rate (or light-gathering power or similar) / per
point / per time interval of exposure, for example.

To me, the Sun & especially the moon appear brighter than others in
the logarithmic scale, but only when taking in to account the idea
that most measurements are not based off of point-sized comparitor
estimates. Or is it better to factor in the extra bonus details of
seeing the 2001-2 Leonid streak and smoke train tails, much the way
that heavens-above.com does for estimating some really bright
point-source artificial satellite estimators?

Probably a classic example of a hard-to estimate point source fireball
is the example below, without taking an averaging over the sum of the
region of which we consider the bolide to be:

http://apod.nasa.gov/apod/ap031001.html

Or does it really make all that much of a big deal for estimate
gathering? For comparing, one of the first 2001 Leonids I saw was
bright enough to cast my shadow, left quite a smoke train & light
tail, but was only a point-source or so wide, during the 10-20 seconds
or so that it lasted at peak. The howling dogs at the next door
farm-yard were also witness to the few other excited RASC Regina
astronomers that night, & soon got the blood rushing after a cozy warm
up in the shelter prior to the observations for most others. I'd heard
of others who'd went scouting down in S. America for telescope sites
that they easily found places whee the Milky Way was in some areas
bright enough to cast a shadow, but wouldn't have remained skeptical,
were it not for such a great meteor-counting night.

Curious amateur RASCer from Waterloo, Ont. area,


Kai


> Wayne:
>        When I first started observing meteors back in the early 1950's it was
> generally accepted that any meteor brighter than -2.0 magnitude was
> considered a fireball.  Today, the generally accepted brightness is any
> meteor brighter than the planet Venus or -4.7 magnitude or rounded off
> -5.0 magnitude.  The RASC Observers Handbook, Fireball Section, uses
> -5.0 or brighter.  Dr. Martin Beech, in his book Meteors and Meteorites
> uses the -4.7 mag number.  The cut off limit for a meteorite dropping
> fireball is around -6.0 or brighter.  One has to be careful here as
> high velocity Cometary fireballs do not drop meteorites as these burn
> up in the atmosphere.
> Ed