Iridiums 27, 31 and Delta Stage

Alexander Seidel (ase@mail.stelljes.de)
Mon, 12 Jan 1998 18:54:05 +0100

Today I report on three more Iridium observations from my site,
including Iridium 27, Iridium 31, and an Iridium Delta R stage:

In order of appearance:

(1) The Iridium Delta Rocket stage (#24874, 97-34 F) made a near
overhead pass (az 283 de, alt 79 deg) in the local evening twilight at
UTC 16:24, height 276 km. It was seen mag +1.0 steady, surprisingly
bright, as it was predicted to be somewhere in the mag +2 ranges.

(2) Iridium 31 (#24950, 97-51 G) performed "an ordinary" flare show at
UTC 16:43:36 (az 52 deg, alt 61 deg). Mirror angle was predicted to be
1.5 deg, with a mag 0.0 prediction from IRIDFLAR and a mag -2.0
prediction from the GSOC site in Darmstadt/Germany. What I really saw
was estimated to be something in between, maybe mag -1 for one or two
seconds.

(3) The "strober" Iridium 27 (#24947, 97-51 D) sureley was the most
exciting view of the three. As yesterday, the pass was nearly overhead,
with az 96 deg and alt 88 deg at highest elevation. I found it with 7x35
binocs east of the Andromeda nebula, high over the southern horizon, and
timed the following flash moments with my 100-lap-times stopwatch:

		UTC 16:51:27,05
		UTC 16:51:30,64
		UTC 16:51:34,17
		UTC 16:51:37,76
		UTC 16:51:41,37
		UTC 16:51:44,94
		UTC 16:51:48,55
		UTC 16:51:52,08
		UTC 16:51:55,74
		UTC 16:51:59,29
		UTC 16:52:02,86
		UTC 16:52:06,54

These timings refine the flash period, measured to be 3.55 (+/- 0.05)
seconds yesterday, to 3.59 (+/- 0.03) seconds this evening.

The satellite was producing sharp, bright flashes in the mag +0.5 to
+1.5 ranges, when I first spotted it, had one single very bright flash
of maybe mag -2 (hard to estimate) near zenith, and then continued to
flash sharply with magnitudes going down to somewhere around mag +3 when
I lost it east of Polaris, where my home=B4s roof intervened.=20
 =20
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Alexander Seidel        N53.5932 E9.4683  6m asl
Stade/Germany           Tel/Fax (+49) 4141 68772
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