[meteorite-list] 1993/94 Perseids - The Night of Lights!

From: bernd.pauli at paulinet.de <bernd.pauli_at_meteoritecentral.com>
Date: 14 Aug 2010 11:54:04 UT
Message-ID: <DIIE.0000005500004EE0_at_paulinet.de>

Hello List,

Some of you may have been surprised when they read about more than
300 Perseids in the Sky & Telescope article I mentioned last night:

'Counts made from western Europe, the Canary Islands, and eastern North
America indicate the maximum zenithal hourly rate (ZHR) topped out at
more than 300 around 3:30 Universal Time on August 12th.'

This would make Kirk's and his friends' observation of 100 and even Greg's
183 look rather "average" but it's not like that at all because ZHR is the
total number of meteors an experienced observer with an incredible 360? view
would see under ideal conditions.

Let's see how ZHR > 300 translates into what was actually observed, i.e. the
actual HR (hourly rate or actual number of meteors observed). The formula for
computing the actual number is:

ZHR = HR x r^ (6.5-LM) / sinA

r = usually 2.5 for the Perseids (called population index)
6.5 = a real dark sky (limiting magnitude of stars you can see)
LM = limiting magnitude in the part of the sky being watched
A = the altitude of the shower's radiant

Assuming almost ideal conditions (on the Canary Islands for example),
let's use LM = 6 and an altitude of 60? of the Perseid radiant (around
01:00 hrs after midnight), ... so we have:

300 = HR x 2.5^ (6.5-6.0) / sin 60?
300 = (HR x 2.5^0.5) / sin 60?
300 = (HR x 1.58) / 0.87
HR = (300 x 0.87) / 1.58
HR = 261 / 1.58
HR = 165

That's the actual number a single experienced person may have been able
to see under favorable conditions, so Greg's Lindh's number (HR = 183) is
quite close to that mathematical result and Kirk's and his friends' HR of
100 Perseids is still a very respectable number of meteors!

Happy Computing,
Happy Observing,
Clear Skies,

Bernd :-)
Received on Sat 14 Aug 2010 07:54:04 AM PDT