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Re: (meteorobs) Fireball mags...
-- [ From: Robert Lunsford * EMC.Ver #2.5.3 ] --
> But, how do you guys estimate really bright fireballs? I agree with
Marco that
> a -19 should probably be called a -20. For myself, I go by the
brightest stars
> and planets, then the moon, and have impressions of magnitudes in the
middle.
>
> When I was observing with Pierre Martin for the Perseids, I asked him
before
> the start of the max night, how he would call the magnitudes for
several
> mercury campground lights in the distance (<behind> where we were
facing!).
> Good exercise for both of us...
>
> I have seen a lot of fireballs under -10, but I think I'd call a -10,
not a -9
> if something was in that range. In other words, the judging gets more
> 'binned'. Something from -9 to -11, I'd probably call a -10.
Likewise, for
> some of the other mags for the bright stuff...
>
> Comments? Any guidelines??? Nighttime guidelines vs. daytime
guidelines, when
> sounds (if any) kick in, how much shadow cast, effect of colour on
guidelines,
> etc....
Experience is your best guide. Having a companion out there also helps
immensely. I use Venus as a guide for fireballs in the -5 to -8 range.
Not that Venus is out every time you see a bright fireball, but it is
fairly easy to recall its brightness and to use that in comparison.
For meteors brighter than -8 I go by the intensity of the flash it
creates and how bright the surrounding terrain is illuminated. I have
been out observing during all phases of the moon and this helps when you
know just how bright a full moon can illuminate the ground.
The duration of any resulting train can be of help. Unfortunately it is
not a strict rule that implies that brighter meteors produce trains with
longer durations. I have seen -4's and -5's with trains of longer
durations than those produced by fireballs in the -7 and -8 range.
Judging fireballs brighter than the full moon is a compromise. You will
have a range of magnitudes you feel comfortable with and usually end up
using a magnitude in the middle of this range. When I witnessed my
brightest meteor back in 1981 I initially gave it a range of -15 to -20.
After a good 10 minutes of hard thought thought I finally settled on -18
figuring it was a bit closer to -20 than -15. I agree with George Z. and
Malcolm that rounding off should be avoided. By the way, the train on
that Perseid lasted 13 minutes (naked eye) and would have lasted longer
had it not drifted into the cone of zodiacal light.
I hope this helps!
Bob