Quote:
Originally Posted by astroron
Looking at this chart, it seems to me that distance equates to brightness 
As you may note the flair that is 41kms away is mag-0.
The flair that is 1km away is mag -8
ridium Flares | Home | Prev. | Next | Help |
Clicking on the time of the flare will load another page with more details,
including a map showing the track of the flare along the ground, and the
location of the nearest point of maximum
Search Period Start: 16:32, Monday, 19 January, 2009
Search Period End: 17:32, Monday, 26 January, 2009
Observer's Location: cambroon observatory ( 26.6394°S, 152.6928°E)
Local Time: Universal Coordinated Time -10 (GMT + 10:00)
Date Local
Time Intensity
( Mag) Alt. Azimuth Distance to
flare centre Intensity at
flare centre
(Mag.) Satellite
20 Jan 19:54:29 -0 60° 80° (E ) 41.4 km (W) -8 Iridium 65
21 Jan 19:48:26 -8 58° 79° (E ) 1.0 km (E) -8 Iridium 68
22 Jan 19:42:24 -0 57° 79° (ENE) 40.5 km (E) -8 Iridium 75
24 Jan 04:27:56 -2 61° 313° (NW ) 18.7 km (W) -8 Iridium 13
25 Jan 04:21:52 -2 62° 315° (NW ) 21.3 km (E) -8 Iridium 50
26 Jan 04:16:06 -3 60° 312° (NW ) 14.9 km (E) -9 Iridium 91 |
Thanks Ron! I'm a bit lost on this, and hope we are not talking at cross purposes! Forgive me if I've misunderstood you, wouldn't be the first time! Just ask Erick, LOL!!
Yes, the brightness that you observe is a function of the distance away (given in km by Heavens Above), but it is the distance away of the flare path on the ground, not the satellite in the sky. The distance away of the actual flare is related to the altitude in degrees given. The table you've provided proves that the brightness of the flare has nothing to do with how close the satellite is to you when it flares. That is, proximity to the zenith per your first post.
"...
the -8 mag is at the center of the flair and that magnitude is usually when the flair is fairly close to Zenith, as it gets further from this point the brightness tapers off"
Anyway, sorry too to you Vincent for hijacking this thread!
As Ron says, the peak of the flare is fairly short, although the entire cycle from when it first starts to brighten to when it dims right off is longer, maybe 15-20 sec.
Iridium flares get pretty addictive, so watch out!
Especially photographing them, which is akin to a precision military operation, LOL! Good luck with your viewing!!
Cheers