Lacrosse 3 R/B, daytime Iridium, full moon
Matson, Robert (ROBERT.D.MATSON@saic.com)
Thu, 16 Dec 1999 12:19:45 -0800
Hi All,
Lacrosse 3 R/B has been making some nice passes the last few
nights in southern California. Its magnitude varies quite a
bit over the course of a zenith pass -- anywhere from 1st
magnitude to under 3rd. The effect is more than what would
be expected from aspect angle and range effects -- perhaps
the Titan is in a slow tumble.
Forgot to mention a couple weeks ago while I was in Aspen,
I managed to catch a -7 (predicted) flare from Iridium 25
on November 29th at ~10:52am MST. Since I was on the
centerline, the maximum flare brightness could not have
exceeded the predicted -7; however, it could easily have
been -6 if the satellite orientation was off a little.
Without references, there's no way to really judge the
intensity other than to say that it was definitely brighter
than -5 (Venus in daytime).
This is the closest to local noon that I've observed an
Iridium flare. I have the clear air and high altitude of
Aspen to thank for this observation -- no way it could have
been seen from the usually hazy daytime skies of the Los
Angeles basin.
And now, about this full moon business. I want to thank Ed
for posting those two links. They confirm the contrarian
remarks I've been e-mailing to the dozens of friends/colleagues
that have been forwarding this "brightest moon in 133 years"
baloney. Whenever I see a story like this, I take great
(perverse?) satisfaction in debunking it.
Yes, it will be a large, bright full moon, and certainly I'll be
watching (more the tides than the moon itself!). Years ago I
wrote a program to calculate and plot tidal force as a function
of time, and at least for my location there were 9 previous times
this century that the tidal force was the same or greater:
Local Relative
Date Stress
---------- --------
1- 4-1912 46.477
12- 7-1919 46.345
1-15-1930 46.384
12-16-1937 46.356
1-26-1948 46.410
12-29-1955 46.446
12-19-1964 46.412
1- 8-1974 46.478
12- 2-1990 46.390
versus:
12-22-1999 46.345
Granted, tidal stress is not the same thing as brightness, but
they are closely related. As indicated in the Sky & Telescope link,
the January 4th, 1912 event is the clear winner.
If you read the original Star Gazer story carefully, it DOESN'T say
that the upcoming full moon will be the brightest in 133 years! Even
the title is clear about this:
"The Astonishing Lunar Illumination of December 22nd, 1999!
The Brightest First Night of Winter in 133 Years! "
"Brightest First Night of Winter" not "Brightest Full Moon in
133 years". Somebody took that story out of context, unleashed
it on the internet, and now everyone thinks that they can drive
with their headlights off on the Winter Solstice! ;-)
Another amusing side note is that all these stories are saying
to look on Wednesday night, December 22nd. Maybe for Europe,
but not the United States! Ignore the solstice -- that has
absolutely nothing to do with moon's brightness. Full moon is
at 12/22 ~17:31 UT. But perigee is at 12/22 10:55 UT. So for
the east coast, full moon is at 12:31pm and perigee is at 5:55am.
Clearly *Tuesday* night the 21st/22nd is the peak night.
What would be interesting is to determine the point on the
earth that will experience the brightest moon. Presumably it
occurs sometime between 10:55 UT and 17:31 UT. Hard to say
which effect is more important: earth-moon distance, or moon-
earth-sun angle. Split the difference for now -- call the peak
time 14:13 UT. What's the moon's longitude and latitude at
that time? Works out that geodetic latitude 20.38 N, 144.26E
is the location on earth where the moon will be at zenith at
this time. This is a little west of the Mariana Islands in
the Philippine Sea.
I hope some enterprising individual will set up a "web cam" in
Piazza San Marco in Venice, Italy. The flooding there should
be most impressive! --Rob
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