Occultations and Grazes during the May 4th Total Lunar
Eclipse - updated 2004 June 28
Rare Naked-Eye Occultation/Graze during the eclipse imaged in
South Africa
Read Daniel Fischer's account of the German expedition to
Namibia for the graze
Movie files of similar graze recorded in Sudan in 1985 are
here
This is in 3 parts:
1. Overview of predictions, and results & pictures of the
alpha 2 Librae occultation and graze in southern Africa
2. Past and Future total eclipse occultations & grazes of
alpha 2 Librae, including my video of the 1985 graze in Sudan
3. Efforts for grazes during this year's May eclipse in Europe
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1. Occultations (total and grazing) of many stars occurred during the
total lunar eclipse of May 4 for observers throughout the Eastern
Hemisphere and northeastern Brazil. Occultations of two 6th-mag.
stars were visible from most of Europe, with grazes of both near
the Pyrenees Mountains (see the bottom of this page for more about
them). Eberhard Riedel's map shows the paths of all
grazing occultations of stars brighter than mag. 9.3 that
occurred against the umbra during the partial or total phases of the
eclipse. Numbers at the ends of the path identify the grazing
occultations that are listed here.
Detailed predictions for individual paths were available from
Eberhard Riedel at E_Riedel@msn.com .
Most remarkable was the occultation during totality of the
2.8-mag. star alpha 2 Librae = ZC 2118 = Zubenelgenubi for observers
in southern Africa, as noted on pages 104 and 106 of my article in
this January issue of Sky and Telescope (with northern limit shown on
the map on p. 103). Alfons Gabel led an expedition to the
deserts of Namibia to observe this rare event, and there were
efforts to observe it in South Africa, as well - for details of this
event, maps, and plans, click here.
Daniel Fischer has a detailed account of the Germans' expedition to
near Fish River Canyon in Namibia, claiming confirmation of the
star's duplicity. Observers in South Africa could get information
about efforts to observe the graze there from Brian Fraser at
fraserb@intekom.co.za .
An observer from Windhoek, Namibia travelled to a small town in or
near the northern-limit graze path for Zubenelgenubi and obtained
some pictures with a 20cm SCT, which I've requested. He expected to
find Alfons Gabel in that small town, but couldn't find him there.
I have some details of that at home. Apparently it was clear along
the graze path across most of southern Africa since I received the
following message from Port Elizabeth, S. Africa, on the s. coast:
From: "franlet"
Subject: Re Occultation during Lunar Eclipse
Date: Thu, 6 May 2004 23:19:23 +0200
I managed to photograph the grazing occultation of double star
Zubenelgenubi during the eclipse of 4 May 2004. Sony 505V DSC
afocally on 10" Meade LX200 SCT
Regards
Dr Francois du Toit
Port Elizabeth
SOUTH AFRICA
His spectacular pictures can be seen here and
here. I believe that Port Elizabeth was
north of the northern limits so that Dr. du Toit actually had a
close miss of both stars, since both are visible in all of his images.
Alfons Gabel reports the mixed results for the Zubenelgenubi
graze from Namibia, where sky conditions were not as good as in
South Africa:
Oh yes, after a wonderful trip across Namibia, an overload of
astronomical and private obligations, and finally some health
problems I'm really in debt to give you my preliminary report
about the graze observations of alpha-2 Librae, Zubenelgenubi,
during the lunar eclipse in May:
One day before the lunar eclipse five observers arrived in the
observing area at the north end of the Fish River Canyon, an
amazing landscape in southern Namibia. In an organizing
meeting, we decided the distribution of the five stations.
During the site inspections on May 4th, the sky was cloudy,
sometimes even overcast, but a loosening cloud cover gave us
new confidence in late afternoon.
Nevertheless the evening became a thriller! It's familiar to
us, that clouds are lit by artificial light, so we usually can
see their outlines, but not so in southern Namibia: Beautiful
sights of comet "NEAT" in the west, but in the eastern sky
where the eclipsed moon should be - nothing but a large
diffuse "coalsack" in the sky! When the critical time
approached, moon and star were sometimes recognizable, but so
scarcely from my station, the northernmost, that I had to push
the camera gain to maximum and to put up with a rather grainy
image. Additionally I needed more exposure time, therefore I
had to reduce the frame rate to 10 fps. Five minutes before
the graze the moon disappeared completely again. Just 26
seconds before the first graze event I could detect the star
on the screen again, but not the moon's rim. I wasn't sure,
whether the first event was an occultation by the moon or by
the cloud. Later inspection revealed that there is doubtless a
lunar occultation. But it will be very difficult to discern
whether dimmings and a possible step event are real. Finally
the situation was much better during the reappearance. A step
event of more than half a second is evident.
Michael Schmidt's and Daniel Fischer's stations were the next
in southern direction. Obviously we had to deal with low
altitude clouds. So Michael was located significantly closer
to the rim of the cloud, Daniel was just outside. So their
disappearance events were much less disturbed. Both had just
one disappearance and one reappearance. Their reappearances
showed a similar step event as in my video. The southernmost
stations of Brigitte Thome and Hans-Joachim Bode failed due to
different technical defects. Brigitte performed visual
timings, at least.
Daniel Fischer, astronomical journalist and publisher of
The Cosmic Mirror
meanwhile was in South Africa again, maybe he still is. We
plan a meeting for next month to evaluate all video results.
Thanks for all good wishes in advance, and for your patience
thereafter.
Friendly
Alfons Gabel
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2. PAST AND FUTURE ECLIPSE OCCULTATIONS/GRAZES OF ZUBENELGENUBI
The last time a star this bright was occulted during a total lunar
eclipse was on May 4, 1985, a 19-year Meton cycle earlier, when the
same star was occulted across most of Africa. In that case, the
southern limit passed over South Africa, where dozens of observers
organized by the late Dannie Overbeek observed the graze, some
without optical aid. The northern limit passed from Algeria to
Somalia; at that time, the only country crossed by that path with
friendly relations with the U.S.A. was Sudan, so Paul Maley, a few
other observers from Houston, TX, and I made arrangements to go
there to observe the event; we had valuable help from the physics
department of Kartuom University and use of a transit satellite
navigation receiver from a local oil company. I managed to video
record the occultation with a cluncky Ultricon camera attached to a
C5; you can see parts of that recording that are in large .avi files
that my wife, Joan, digitized from a time-inserted copy of the
orginal tape. The interesting first part of the graze, with 9
events, can be downloaded (it's 226 megabytes) here
(that's recommended, then view it from your hard drive, otherwise it
will load into your viewing software much slower than real time), and
the segment containing the final reappearance (53 megabytes) can be
downloaded here. I hope that someone can
record this year's event with one of the sensitive video cameras that
are available now (and much cheaper than the Ultricon!), possibly one
in color, to show the eclipsed part of the Moon much better.
Several years ago, Jean Meeus wrote an article about lunar eclipse
occultations, examining all possibilities up to 2050, and some
beyond. He and G. P. Konnen published it as "Occultations of Bright
Stars by the Eclipsed Moon" in Journal of the British Astronomical
Association, Vol. 85, No. 1, pp. 17-24 (1974). After May 4th this
year, there will not be another chance to observe an occultation of
a 3rd-mag. or brighter star until May 6, 2050, when Zubenelgenubi
will again be occulted by the totally eclipsed Moon. Unfortunately,
that event will be visible only from Antarctica, and at low altitude
from the Falkland Islands and Tierra del Fuego; the northern limit
passes entirely south of South Africa.
Jean Meeus also predicts a better Zubenelgenubi eclipse occultation
for 2069 May 6, a Meton cycle after the 2050 event. He writes:
"This will be a total eclipse of magnitude 1.32 or 1.33. Maximum
eclipse will occur at 09:07 UT. The Moon will be totally eclipsed
from about 08:25 to 09:49. The occultation of Alpha Lib will be
visible in a zone that is mostly over water (the Pacific Ocean), but
that will also include a part of South America."
It is a rather good event, visible from many South Pacific islands
(a good excuse to go to Tahiti or Easter Island!), and from the deserts
of Peru and northern Chile. A map showing the region of visibility
of this occultation generated with Occult by Denis Denissenko is here;
I was able to produce a similar map with Occult. Unless medical
science finds a way to stop aging, I won't make it (I would be 125
then), but maybe my son might observe it, and certainly any children
he has might see it.
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3. EFFORTS FOR ECLIPSE GRAZES IN EUROPE
Returning to this year's eclipse, the southern-limit graze paths for
both ZC 2111 (mag. 6.9) and ZC 2119 (mag. 6.5) cross the southernmost
part of France, near Pic du Midi Observatory, and the paths seem to
intersect just north of Andorra; it would be interesting to travel to
the intersection place to observe both grazes without having to move.
In northeastern Spain, Carles Schnabel of the Agupacio Astronomica de
Sabadell, e-mail planetari@ctv.es , wrote:
"We are preparing an expedition to observe the grazing occultation of
ZC 2119 on the [Mediterranean] coast, between Girona and Barcelona,
exactly between Malgrat and Calella. This event occurs during the
totality of the lunar eclipse, so it may be an extraordinary
phenomenon. You are invited to join our expedition."
I have not heard yet whether or not they were successful. I think
they were clouded out (some other observers in France reported bad
weather for the eclipse) since if successful, I think I would have
heard from them by now.
David Dunham