Heavens-above predicted a -8 mag iridium flare visible from my place this am. Waited for it with high hopes but it was very dim not even as bright as Sirius.I must say the time and location was accurately predicted though.
Any similar experience from this forum's members? Was it common for brightness turned out significantly different?
At mag -8 one would think it would be close to nearly overhead, so should be as expected
What time of morning and sky conditions did you have, and was it overhead?
I normally find that the place in the sky can be a little out for where it flairs
but find the mag to be quite close to the mark
Thanks for your reply astroron.It was 4:15am this morning. Altitude 47 degree in the west (far from overhead)travelling from south to north. This was my first iridium flare observation. I saw it brighten up but even at its max its still much dimmer than Sirius which was not far away.
Thanks for your reply astroron.It was 4:15am this morning. Altitude 47 degree in the west (far from overhead)travelling from south to north. This was my first iridium flare observation. I saw it brighten up but even at its max its still much dimmer than Sirius which was not far away.
Vincent, at 47degrees and at that time of the morning it would be a fair way away from you and the sky would have been getting brighter, 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
Keep watching, I am sure you will see mag-8 soon
We watched a -7 last night at 9:30, 62 degrees altitude in the east. It was pretty spot on, Venus was over in the West and it was much brighter than that. Sirius was nearby too, and it was much much brighter that it.
Hi Vincent! I'm a bit of an Iridium flare freak and have always found the info given on Heavens Above to be spot-on in time & magnitude. EXCEPT for one embarrassing episode at Snake Valley, Vic, where a promised mag -8 flare failed to eventuate. But I think that was 'pilot error' - ie I must have mucked up the location or something.
Re astroron's comment about mag -8 flares being close to overhead, I don't think that's quite right. They can be pretty much anywhere.
Hi Vincent! I'm a bit of an Iridium flare freak and have always found the info given on Heavens Above to be spot-on in time & magnitude. EXCEPT for one embarrassing episode at Snake Valley, Vic, where a promised mag -8 flare failed to eventuate. But I think that was 'pilot error' - ie I must have mucked up the location or something.
Re astroron's comment about mag -8 flares being close to overhead, I don't think that's quite right. They can be pretty much anywhere.
Cheers -
According to "Heavens Above" the further away from your location the flair is the dimmer it is for you at your location
If you where undernieth it it would be -8, subject to how much sunlight it may receive. It would not be mag -8 for you at your location if the flair was forty kilometers away.
That is my understanding of what" Heavens Above" is telling me.
I will stand corrected if anyone can more enlighten me
Hi Vincent! I'm a bit of an Iridium flare freak and have always found the info given on Heavens Above to be spot-on in time & magnitude. EXCEPT for one embarrassing episode at Snake Valley, Vic, where a promised mag -8 flare failed to eventuate. But I think that was 'pilot error' - ie I must have mucked up the location or something.
Re astroron's comment about mag -8 flares being close to overhead, I don't think that's quite right. They can be pretty much anywhere.
Cheers -
Thanks Ron & Rob for your input. What frustrated me was Heavens-above's timing and location in the sky was spot on. Only the brightness was way off. My place was predicted a -8 mag, same as the centre of flare which was only 1 km away. I wonder if altitude of location plays a part in all this?
My place is some 40m above sea level??
Vincent, the only thing I can think of is that the angle of the Solar Panels was a bit off and so was not as bright as predicted.
My place is 125m above sea level which makes no difference at all.
Cheers
It also has to do with which Iridium satellite it is.
There are some floating up there that do not have much in the way of attitude control and therefore the orientation of their panels is not what might be expected compared to those that are being used. Check which satellite it is, there is usually a marker of some sort on the information to give an indication of whether the satellite is active or not.
I have also recently witnessed the brightest satellite flare I have ever seen - it was way brighter than -8 and I could not find a prediction for it when consulting various predictive sites for a check of the back catalog as it were. It was spectactular and fairly short. Sometimes the orientation is just so. I can also imagine if I happen to have it cross my eyepiece at that time that I'd need some time to re-dark adapt!
I regularly see satellites cross the eyepiece these days to the point of being annoying rather than novelty. I did a quick check a few times to find out that most of the ones I was seeing were the bits and pieces of the former Chinese satellite that was engaged in an ASAT test. Translating one piece of space junk into many, yeah that is a good idea.
According to "Heavens Above" the further away from your location the flair is the dimmer it is for you at your location
If you where undernieth it it would be -8, subject to how much sunlight it may receive. It would not be mag -8 for you at your location if the flair was forty kilometers away.
That is my understanding of what" Heavens Above" is telling me.
I will stand corrected if anyone can more enlighten me
Thanks Ron, it's an interesting one. I went back & checked flare predictions at a number of my inputted places on Heavens Above. One particular place had a mag -8 at 11 deg altitude, and the next day a mag -2 at 71 deg altitude. So an Iridium can pass overhead, but you might only get a fraction of the full reflection. Or it can be some distance away (low) and you can cop the full reflection. I know from experience that none of the mag -8 flares I have photographed has been particularly high in the sky, but no doubt if I keep shooting them one will be on the law of averages.
Edit: In summary the brightness is a function of your closeness to the flare path, not the satellite (although obviously the amount of air you're viewing through must have a minor influence).
Cheers -
Last edited by Rob_K; 19-01-2009 at 04:24 PM.
Reason: Summary!
Here's a couple of shots of a mag -7 flare taken from my place on Christmas Day. Not quite mag -8, but it was incredibly bright anyway! As you can see from the second (uncropped) shot, it was very low to the horizon, barely over the tree-tops.
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 intensity.
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
Guys, what duration would you normally expect these flares to last. Is it only a split second, a few seconds, etc.
Usually they start to brighten and then flair then fade slowly over about 3 to 4 seconds.
If you have Bino's you can watch the satellite for a short while before it dissapearse into the Earth's shadow
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!!
Thanks again for both of you Ron & Rob for sharing your valuable experiences. I am only new in iridium flare chasing,saw only 2 dim ones so far. I looked up the disappointing one: it was iridium 19, a "spare satellite which orbit might be a bit unreliable" as warned in Calsky. From now on I will focus on those active ones hopefully get better result.
Cheers
not even as bright as Sirius.I must say the time and location was accurately predicted though.
Vincent, at 47degrees and at that time of the morning it would be a fair way away from you and the sky would have been getting brighter, 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
But I think that was 'pilot error' - ie I must have mucked up the location or something.
Especially photographing them, which is akin to a precision military operation, LOL! Good luck with your viewing!!
