re: Iridium 20 rotation axis; OBS: 66 timed flashes
Walter Nissen (dk058@cleveland.freenet.edu)
Wed, 17 Jun 1998 12:53:16 -0400 (EDT)
> The bottom line is that more measurements are needed. For each data
> point I only require the following information:
Rob, and others interested,
Before I launch into my OBS, I want to point out, to beginners and those
who have hesitated to become involved with precise OBS, that all of the
below was done with an inexpensive stopwatch (albeit one with 100
splits/laps) and an inexpensive shortwave radio. If you want to skip the
radio, if you are in the CONUS (continental US), you can pay $.50 to call
1-900-410-TIME, or if you are in the UK, you can listen to the 6 pips on
BBC. As I understand it, for some time now, the 6 pips have been given in
UTC, not GMT, despite the incessant repetition of that epithet. Other
national time services have made other provisions for the distribution of
accurate time.
As it happens, I was in the process of puzzling over a detailed OBS I made
of 24871 when your message arrived, so I made a quirky adaptation
necessitated by my new stopwatch environment, and used an old program I
wrote years ago to facilitate reporting of rotation axis data to Bart, to
produce the report below to respond to your request.
It occurs to me, there may have been a simplified format proposed or
adopted for this data, but I'm not precisely sure where to look for that.
Between 19980616 025152.68 and 025448.49 UTC, an interval of 175.81 s, I
recorded every bright (this means perhaps mag 4? or brighter) flash from
24871. There were 66 of these. Mnay were at intervals of nearly 1 s,
though I haven't yet done a regression to obtain a mean for them. I'm
still thinking about the details of choosing the interval(s) for that, and
welcome suggestions.
The accuracy I recorded for these splits is .4 s, though I think the
internal consistency suggests .2 is more realistic. I have not applied
any personal equation, but .2 or .3 s would be appropriate.
During this interval there were 3 occasions when the intensity of the
flashes, or brightness, began to rise, reached a maximum and dropped
again. The flashes came so close together that, probably mistakenly, I
decided in real time not to try to use false "double" splits to mark the
maxima, so I have only my vague recollections recorded immediately after
the OBS to establish when these bright maxima occurred. Using splits,
numbered 0 to 65 as below;
there was one in the general area of # 7 thru #17, which reached mag -1?;
a second one in the general area of #42 thru #52, which reached mag 1?;
and a third in the general area of #57 thru #62, which reached mag 1?.
These interval numbers are probably +/- 5 or so. The range of numbers
given only mildly suggests how wide the humps of the maxima lasted, but is
intended to specify the possible times of the increased brightness. Had I
been looking naked-eye, I imagine the first of these maxima would have
looked a lot like an airplane with a strobe.
Probably most of the timed flashes were about mag 4? or so. There was
considerable variation noted even while the fluctuations were not definite
enough to record accurate timings. I had very little difficulty following
the object at mag 5 or 6 between flashes.
I would be happy to produce one or more PPAS-format reports of this OBS,
if someone would suggest the most desirable way(s) to do that. I know how
to report when the timings are consistent, but confusion confuses me.
Could the interval of 1.53 s between splits #44 and #45 be a synodic
anomaly, such as Bart and Patrick Wils have written about? If you think
24871 is a polished cylinder and look only at splits #35 thru #50, would
you have to think so? Of course, it's not a cylinder, but ...
(The computed mean is obviously nonsense).
The state of vulgar names being rather odious at the present time <as if
it were ever different ! 8->, I should point out that some of you probably
think Ir 20 is Ir 18, and maybe something else. Whenever a confusion of
vulgar names arises, please always specify the catalog # and COSPAR ID.
I also have have (somewhat less) detailed OBS of earlier passes of
tumblers Ir 11 and 27.
I apologize to many of you (especially to Mike) (and Bruno, too) for the
poor quality and timeliness of my correspondence.
Cheers.
Walter Nissen dk058@cleveland.freenet.edu
-81.8637, 41.3735, 256m elevation
---
Statistical stupidity: believing everything within 2*sigma is true and
everything beyond 2*sigma is false. E.g., 6 consecutive tails is impossible.
---
Subtract -0.49s
2 51 52.19 2 51 52.68
2 51 53.00 2 51 53.49 .81
2 51 53.96 2 51 54.45 .96
2 51 54.83 2 51 55.32 .87
2 51 55.80 2 51 56.29 .97
2 51 56.77 2 51 57.26 .97
2 51 57.80 2 51 58.29 1.03
2 51 58.74 2 51 59.23 .94
2 51 59.71 2 51 60.20 .97
2 52 0.69 2 52 1.18 .98
2 52 1.56 2 52 2.05 .87
2 52 2.51 2 52 3.00 .95
2 52 3.49 2 52 3.98 .98
2 52 4.42 2 52 4.91 .93
2 52 5.36 2 52 5.85 .94
2 52 6.44 2 52 6.93 1.08
2 52 7.49 2 52 7.98 1.05
2 52 8.40 2 52 8.89 .91
2 52 9.41 2 52 9.90 1.01
2 52 10.56 2 52 11.05 1.15
2 52 11.72 2 52 12.21 1.16
2 52 12.50 2 52 12.99 .78
2 52 13.44 2 52 13.93 .94
2 52 14.31 2 52 14.80 .87
2 52 15.26 2 52 15.75 .95
2 52 16.25 2 52 16.74 .99
2 52 19.25 2 52 19.74 3.00
2 52 20.69 2 52 21.18 1.44
2 52 23.08 2 52 23.57 2.39
2 52 24.15 2 52 24.64 1.07
2 52 25.00 2 52 25.49 .85
2 52 26.00 2 52 26.49 1.00
2 52 26.92 2 52 27.41 .92
2 52 27.70 2 52 28.19 .78
2 52 28.80 2 52 29.29 1.10
2 54 14.76 2 54 15.25 105.96
2 54 15.53 2 54 16.02 .77
2 54 16.36 2 54 16.85 .83
2 54 17.25 2 54 17.74 .89
2 54 18.29 2 54 18.78 1.04
2 54 19.26 2 54 19.75 .97
2 54 20.25 2 54 20.74 .99
2 54 21.36 2 54 21.85 1.11
2 54 22.36 2 54 22.85 1.00
2 54 23.47 2 54 23.96 1.11
2 54 25.00 2 54 25.49 1.53
2 54 26.01 2 54 26.50 1.01
2 54 26.91 2 54 27.40 .90
2 54 27.77 2 54 28.26 .86
2 54 28.78 2 54 29.27 1.01
2 54 29.83 2 54 30.32 1.05
2 54 34.52 2 54 35.01 4.69
2 54 35.51 2 54 36.00 .99
2 54 36.45 2 54 36.94 .94
2 54 37.42 2 54 37.91 .97
2 54 38.26 2 54 38.75 .84
2 54 39.24 2 54 39.73 .98
2 54 40.25 2 54 40.74 1.01
2 54 41.25 2 54 41.74 1.00
2 54 42.27 2 54 42.76 1.02
2 54 43.25 2 54 43.74 .98
2 54 44.25 2 54 44.74 1.00
2 54 45.36 2 54 45.85 1.11
2 54 46.18 2 54 46.67 .82
2 54 47.03 2 54 47.52 .85
2 54 48.00 2 54 48.49 .97
Total 175.81 / 65 = 2.70
98 6 Year and month (2I5)
41.3735 -81.8637 256. lat, long, hgt (3F10.0)
16 2 51 52.68 65 Start day,hr,mn,sec nbr timings
0.00 0
0.81 1
1.77 2
2.64 3
3.61 4
4.58 5
5.61 6
6.55 7
7.52 8
8.50 9
9.37 10
10.32 11
11.30 12
12.23 13
13.17 14
14.25 15
15.30 16
16.21 17
17.22 18
18.37 19
19.53 20
20.31 21
21.25 22
22.12 23
23.07 24
24.06 25
27.06 26
28.50 27
30.89 28
31.96 29
32.81 30
33.81 31
34.73 32
35.51 33
36.61 34
142.57 35
143.34 36
144.17 37
145.06 38
146.10 39
147.07 40
148.06 41
149.17 42
150.17 43
151.28 44
152.81 45
153.82 46
154.72 47
155.58 48
156.59 49
157.64 50
162.33 51
163.32 52
164.26 53
165.23 54
166.07 55
167.05 56
168.06 57
169.06 58
170.08 59
171.06 60
172.06 61
173.17 62
173.99 63
174.84 64
175.81 65
elset courtesy the new OIG Web Site (last 5):
IRIDIUM 18
1 24871U 97034C 98166.11603432 +.00000239 +00000-0 +77629-4 0 02100
2 24871 086.3997 042.5709 0015139 067.8538 292.4281 14.34525971048932