Iridium, OBS, extremely bright glint evening after tomorrow

Walter Nissen (
Fri, 29 Oct 1999 14:37:41 -0400 (EDT)

A week ago, on the spur of the moment, I sent out a brief note to some
observers in Ohio, mostly northeastern Ohio, suggesting observations of a
glint from Ir P36  61.  I think the results are pretty interesting, and by
posting them to SeeSat-L, I hope to encourage others to observe
successively and in groups and to try to nail down the attitudes of as
many Iridia as possible.

On Sunday evening, another opportunity will occur.

My first target was chosen because she has earlier produced glints which
were brighter or fainter than predicted.  A summary of the OBS appears

Note that the glint measured by me was asymmetric.  It rose much more
slowly in brightness than it declined.  Why?

If any of you can improve on my conclusion, I would very much like to
hear your opinion or your calculation.  Here is my interpretation:  The
glint path passed well to the East of the predicted path.  How much?

If you are close enough in longitude to northeastern Ohio to be able to
participate with us, I would be happy to add you to my list of prospective
observers, but you should know that I am near Lake Erie where the next 4
or 5 months will be pretty cloudy.

Thanks to all.  Good job, observers.

The next opportunity for Ir P36 in this general vicinity is predicted for
Western Ohio, and points North and South of there, but perhaps it will
shift quite a bit to the East, as it apparently did last week.  How far??
Somewhere around here, it will be fabulously bright.  This one will appear
nearly halfway up in the SSW, 38 degrees altitude over azimuth 196
degrees.  You may wish to begin looking about a minute early at 23:23:30
UTC which after the so-called "time change" earlier that morning will be
6:23:30 pm EST.

                      Iridium Coordinates  Range   Sat   Solar
Peak  Std    Maximum Flare
Ir   Date      Time    Azm El   RA   Decl  (km)  N Ill Azm  Elev M FlrAng
Mag  Mag  Mag Latitude Longitude
61 99-10-31 23:24:10.0 199 43 19h41  -3.9 1082.3 D Lit 261 -11.2 R 11.48
5.9 -7.5  5.1  41.8538  -84.4046
61 99-10-31 23:24:30.0 196 38 19h45  -9.6 1178.9 D Lit 261 -11.3 R 10.33
5.8 -7.3  4.8  40.6830  -84.3201
61 99-10-31 23:24:40.0 195 35 19h47 -12.1 1230.3 D Lit 261 -11.3 R 10.40
5.9 -7.2  4.8  40.0970  -84.2797

Opportunities are continually occurring all over the surface of the Earth
for observing this object and others.  If you wish to participate, y'all
will have to organize yourselves, though I will try to offer what
assistance I can.


Walter Nissen         
-81.8637, 41.3735, 256m elevation


Did you know?:
A tumbling satellite may exhibit quite different flash patterns on
different legs of the same pass?


Summary of observations:

Observer     Location          time             observed
RD      -81.3437 41.5145  19991021 235715?      -5 or -6             -1.5
RR      -81.4320 41.0818  19991021 23           -4 or -5?            -7.7
"Akron" -81.5122 41.0833                                             -8.0
Copley  -81.65   41.1?    19991021 23           0 or -1??            -1.7?
WIN     -81.8637 41.3735  19991021 235715.42    0?                     .5
GN      -83.01   40.06    19991021 23           fainter than mag 2    4.1



Ir P36  61
located mag 6??                         19991021 2356 7.53
up to mag 5?                            19991021 235628.78
rose in brightness very slowly
up to mag 4?                            19991021 235652.62
glint mag 0? naked eye dtm              19991021 235715.42
down to mag 5?                          19991021 235734.73
lost mag 6?                             19991021 2358 6.03
personal equation of about .25 s not applied
dtm means time was difficult to measure, hence could be 2 to 4 s late

Ray Dabkowski, rayd, OBS:

Thanks for the "heads-up".  It was an awesome display.  I didn't have an
ultra-accurate clock with me, but here in Chesterland ( Lat. 41.5145,
Long. 81.3437) the glint occurred about 19:57:15 (+/- 5 seconds): about a
minute later than you had posted [I had suggested beginning about 1
minute early - WIN]. I would estimate the magnitude between -5 and -6.

Gerald H. Newsom, gnewsom, OBS:

There were scattered thin clouds here, with the waxing gibbous moon not
from the predicted location of this Iridium flare.  I didn't see any sign
of the flare, so it must have been fainter than at least mag. 2.  My
location is lat 40.06 N, 83.01 W.

BOB ROSE, robert.rose, OBS:

I'm in Akron at 41.0818, -81.4320 and was able to see the flare, but it
was though some light clouds right on the edge of fairly dense cloud
GSOC estimated -7 for my location. I don't think it was that bright. I
would guess it was in the -3 to -4 range through the cloud cover and maybe
-4 to -5, without the clouds. There were enough clouds to produce a halo
the entire time the flare was visible.

A friend of mine in Copley also saw it and said it was not very bright. He
has only seen a couple of these. I would give a wild guess at 0 to -1
on his description.

Thanks for sending me your notes.


Ir P36  61
1 25263U 98018B   99295.59810307 -.00000166  00000-0 -66338-4 0  1910
2 25263  86.4006 132.9497 0002645  81.8373 278.3126 14.34214911 82724


IRIDFLAR prediction for "Akron, OH":
Latitude:  41.08330  Longitude:  -81.51220  Altitude:  270.0 m
                      Iridium Coordinates  Range   Sat   Solar
Peak  Std    Maximum Flare
Ir   Date      Time    Azm El   RA   Decl  (km)  N Ill Azm  Elev M FlrAng
Mag  Mag  Mag Latitude Longitude
61 99-10-21 23:56:30.0 140 62 21h46  17.8  875.1 D Lit 269 -15.1 R 14.81
5.5 -8.4  5.7  43.6473  -81.7100
61 99-10-21 23:57:16.1 156 46 21h36  -0.4 1035.4 D Lit 269 -15.3 R  0.14
-8.0 -8.0 -8.2  41.0825  -81.4821
61 99-10-21 23:58:10.0 164 32 21h28 -15.1 1301.6 D Lit 269 -15.4 R 10.72
5.7 -7.4  4.9  38.0829  -81.2497


Text of my note which accompanied the elset and the prediction from Rob
Matson's IRIDFLAR:

Some of us are very likely to be irradiated, er, Iridiated, by a near
maximal Iridial glint this evening; about 20 times brighter than Venus;
magnitude -8.  The spacecraft in question, Iridium P36  61, has developed
something of a reputation as a rogue, giving off glints which do not
closely match the predictions.  Apparently it's tilted a bit more than
most.  If you can provide a rough, or better, magnitude estimate and your
exact location, preferably latitude and longitude, maybe we can find out
what the tilt is.  Nominally the center of the glint path goes straight
thru Akron from North to South, but I'm pretty sure that's not going to

I'm not sure when it will cloud up, but the event may occur early enough.
At 23:56:15 UTC, 7:56:15 pm EDT, trying to begin a minute early or so,
look halfway up in the SSE, 46 degrees over 156 degrees azimuth, and try
to remember how bright Venus looks in the morning sky, I guess.

Thanks for any data you can produce.


[End of message sent a week ago]

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