(meteorobs) Re: Question about fireball brightness

[Ed Cannon]

In reply to my question, George Zay wrote (in part):

> "How bright does a meteor must be to light up objects
> and produce noticeable shadows? " I believe a meteor
> in the neighborhood of -4 will produce shadows.

Thank you, George, for the reply.  Partly for my rule of
thumb I was interested in the factor of local limiting
magnitude.  If a -4 is bright enough where LM is +6.0
(i.e., ten magnitudes brighter than local LM at the time),
is -4 still bright enough where LM is +4.0 (only eight
magnitudes brighter than local LM)?

I mentally tried to compare it to the many bright Iridium
flares I've seen, which theoretically can be theoretically
as bright as -8 (rarely -9).  But as Jan wrote, above -5
or -6, it gets hard to tell.  I saw a very bright Iridium
flare once near the Moon, and it was obviously more
intensely bright than the Moon's intrinsic brightness, but
the Moon was no doubt brighter overall due to it being a
lot bigger, even if not as intense as the Iridium.

In relation to this it just came to me that if there's a
-4 fireball that stays -4 for one second, covering a number
of degrees of sky during that time, that's certainly
a different case in some way than the small stationary disk
of Venus.

I've inquired of amateur astronomers in Austin and San
Antonio, but none of them that I've heard of so far saw
this one.

Ed Cannon - Austin, Texas, USA