VIEWING THE ECLIPSE FROM BULGARIA
		
		KEN PHILLIPS (RUTHERFORD APPLETON LABORATORY)
		
			November 1999
			

Up till last year I had never seen a total eclipse of the Sun which is
remarkable considering I have made solar physics my career and was interested
in observing the Sun as an amateur astronomer back in the 1960's. The impetus
for going to the eclipse in February 1998, in the Caribbean, was really a
committee that had been set up at the laboratory where I work, Rutherford
Appleton Laboratory, to steer UK activities for the eclipse of August 11, 1999.
Someone had suggested that it would be a good idea to "showcase" UK solar
physics activities by conducting an experiment to observe the eclipse. Almost
simultaneously one of my colleagues had been drawing my attention to a new
electronic (CCD, standing for charge-coupled device) camera which could record
images at very fast frame rates (up to 70 frames a second) with digital output.
It was designed by EEV, the Chelmsford company making them for scientific, and
in particular astronomical, purposes. These cameras seemed very exciting, and
at the time I thought it would be highly useful to see if they could be put on
to a solar optical telescope to record the way the photospheric granules
evolve. But I also became interested in experiments that Prof. Jay Pasachoff
and colleagues from Williams College, Massachusetts, had done in searching for
fast changes in the solar corona. There was equivocal evidence from these
searches, made during a number of total eclipses in the 1980's, that there were
periodic modulations in the coronal intensity which pointed to the long-elusive
heating mechanism of the solar corona being magnetic waves
(magneto-hydrodynamic, or MHD, to be precise). The solar corona is the very
hot, but tenuous, "atmosphere" of the Sun which is not visible to the naked eye
at all unless the brilliant solar photosphere is blotted out by the Moon, i.e.
during a total solar eclipse. After 50 years of close study, both by
observational astronomers and theorists, the exact heating mechanism of the
solar corona is still unknown, though it is undoubtedly connected with the weak
magnetic field pervading the corona.

As interesting as solar granules are, it seemed to me, back in 1997 when the UK
solar eclipse committee was set  up, that searching for the modulations that
Pasachoff had reported  with the new EEV cameras would be highly
relevant to the long-standing solution of the corona's high temperature. Of
course, many very sophisticated experiments, many on spacecraft such as the
Japanese Yohkoh satellite and the ESA/NASA mission SOHO (Solar and Heliospheric
Observatory), have looked at the same question in the past. However, all
previous experiments have really concentrated on getting the maximum "spatial"
(or angular) resolution rather than the crucial question of time resolution.
The reason time resolution is of such importance is that theory predicts that
if magnetic waves are really important for solar coronal heating, the periods
of the waves should be very short -- perhaps only a few seconds. However,
imaging with the ultraviolet and X-ray instruments aboard Yohkoh and SOHO, for
instance, is necessarily a slow business. Images are generally built up by
scanning or by CCD cameras adapted for the X-ray range, and with the
limitations of spacecraft telemetry, images of even small portions of the
corona will take about 2 minutes or so to form. So a wave travelling through
one of the numerous loop structures making up the corona or causing modulations
in the intensity with periods of a few seconds will be completely unnoticed in
spacecraft imaging. 

With my colleague Pete Read at RAL, then, we drew up a preliminary design for
an instrument that could image the solar corona during an eclipse with the new
EEV cameras at very fast rates and with a spatial resolution matching those of
spacecraft. I dubbed it the "Solar Eclipse Coronal Imaging System", or SECIS.
One development that gave great impetus to our work was the offer of a clever
software means of "grabbing" the images from the cameras and putting them into
the disk storage of a specially adapted PC. This was done by a small computer
firm in Maidenhead, 4C's (Carr-Crouch Computer Company) who have done a
marvellous job for us in making equipment and designing software that could be
carried out into the field for doing our experiments. Of course, like any
science research enterprise where the output is uncertain we had problems with
the funding of the instrument, but we eventually got some funds for the
equipment itself from RAL. At a late stage, I decided that going to the eclipse
in February 1998, visible in the Caribbean, would be a very good idea,
preparatory to the 1999 eclipse, so we hurriedly made preparations to go to the
French West Indies island of Guadeloupe. By this time I was joined by my
colleagues at Queen's University Belfast, where I have a visiting professorship
through the head of the Astrophysics Group there, Prof. Francis Keenan. Prof.
Keenan got funding for our trip to the Caribbean through the Leverhulme Trust. 
Peter Gallagher, then a PhD student, joined me in the Guadeloupe expedition
along with Francisco Diego, an experienced "eclipse chaser" familiar to lots of
people from many television appearances before the 1999 eclipse. We met up with
Dr Serge Koutchmy, also an eclipse chaser, from the Institute of Astrophysics
in Paris, who organised a site for us in the island. We were lucky enough to
have extremely clear skies but in the event very unlucky as almost literally at
the last minute there was a failure in the power supplying our and everyone
else's equipment at the site. It was not a pleasant scene!

Not too deterred by this, we then made plans to use the SECIS cameras on a
coronagraph at the National Solar Observatory/Sacramento Peak, situated in
southern New Mexico. This was at the invitation of Dr Ray Smartt who works
there and whom we met in Guadeloupe. Peter and I and Pete Read went out there
in August 1998 and, though the trip wasn't without problems (one of the cameras
developed a fault and the skies were surprisingly cloudy) we eventually got
some nice images of the corona (Fig. 1). Peter Gallagher was in fact the one
who got these images,  as I had to return home for a conference by September.
He did a very preliminary analysis and on the face of it there is evidence for
modulations in coronal intensity in the coronal loops above an active region
(associated with large sunspots) on the Sun's west limb visible in the figure.
So this was encouraging.

We were now joined by a team of seasoned solar observers from the Astronomical
Institute, University of Wroclaw, in south-western Poland, consisting of Prof.
Bogdan Rompolt, Dr Pawel Rudawy, Arek Berlicki and Adam Buczylko. They had
funds approved to build a high-precision heliostat or tracking mirror (Fig. 2)
which could provide a horizontal beam of sunlight for the SECIS instrument
which we now designed to be built on a horizontal optical bench. We were still
not quite sure that the cameras would be sensitive enough to record the solar
corona despite the tests in Sac Peak, so we did some more tests in Poland last
May on the full Moon (which has approximately the same surface brightness as
the corona) in Poland, using the Wroclaw heliostat. Things seemed to work out
reasonably well. Unfortunately there was a delay in the despatch of the SECIS
instrument back to the UK and this had serious impact on our final preparations
for the August eclipse. In fact things were very fraught indeed in the days
leading up to the despatch of the equipment out to Bulgaria, where by agreement
with Prof. Vlado Dermendjiev at the University of Sofia we had arranged to view
the eclipse. Thing after thing seemed to go wrong -- at one point we even had a
minor fire; one of the tiny cooling fans on the cameras had a short and the
wires melted and the insulation caught fire! I had arranged to fly out to
Bulgaria myself on July 31, some two weeks before the eclipse, and eventually
Peter Gallagher from Belfast, Robin Barnsley from the JET Laboratory in Culham,
plus our Wroclaw colleagues, were all ensconced in hotels or beach bungalows in
the site, a small seaside village called Shabla, on the Black Sea. At first
things were not auspicious at all: the weather started off very stormy, and
Peter and I were amazed one day sitting at a beachside cafe drinking our
cappucinos  to witness a fully fledged tornado out at sea! Fortunately it
didn't come our way. The Polish heliostat arrived and Pawel and colleagues set
it all up, using time-honoured ways of aligning it to the local meridian. But
no sign of our equipment! There had apparently been a most unfortunate delay in
the UK in the "Carnet" process that was supposed to steer the equipment through
UK and Bulgarian customs. We had a desperate time trying to persuade people to
hurry the thing along, using the one and only pay phone in Shabla. I was most
grateful to Dr Maria Madjarska, who is a postdoctoral fellow in Prof.
Dermendjiev's group, who did a lot of shouting and screaming down the phone
line for me, in a mixture of English and Bulgarian. 

Eventually our kit arrived, the morning of August 10, the day before the
eclipse! To add to our troubles, the hotel we were staying at threw a wobbly
and after much stress I decided to check out and go into other accommodation.
One good thing -- the weather had brightened up considerably and we were
blessed on the morning of the eclipse by perfect weather. The totality was
predicted for 1410 local time. By mid-morning the SECIS equipment and the
heliostat were all at the ready. Anyone who has been to an eclipse will know
the feeling of suspense that we experienced that morning. Through the hotel
hiccup, I had skipped breakfast and didn't much feel like lunch either. When
totality came, still with cloudless skies, everything seemed to work like a
charm. We started exposing the cameras at precisely the moment of second
contact, and ran for precisely 2 minutes and 20 seconds, the predicted duration
of totality. There were ooh's and aah's from the many people at the site around
us during the totality whilst I and my colleagues were ourselves gaping at the
incredible spectacle in the sky. I am not sure whether my conscious mind was
properly in gear at all at that moment but I do remember being awestruck by not
only the marvellous intricacy of the corona through binoculars but the
seemingly enormous number  of bright pink prominences distributed all round the
solar limb. Fantastic! Peter and others were whooping with joy the instant
totality was over, and I do vaguely remember Bulgarian high-alcohol beers being
handed around in profusion. Drinking on an empty stomach is not, as I remember
from student days, an activity to be recommended! The rest of the day fades
almost into oblivion, but one thing I do remember, with great delight was when
Peter played the SECIS images back on our computer monitor and there, in both
channels, was the corona and in one of the channels all the prominences we had
witnessed with our eyes moments before. We had captured 12,728 images in the 2m
20s of the totality, and could look forward to lots of data analysis and
learning about Fourier transforms. 

Figure 3 shows just one of these thousands of SECIS images, compared with SOHO
ultraviolet images either side (they show the corona and chromosphere on the
solar disk as well as the solar limb). Right now, we are all busy trying to
search for modulations or other fast changes. Looking at the movie, one could
perhaps make the claim that there are tiny "coronal mass ejections" taking place
in one of the coronal active regions, though we need to look at this more
carefully. Unfortunately Peter Gallagher has joined the brain drain and has
taken up a postdoctoral appointment in New Jersey, but I hope we will still have
his expertise at least remotely. Our Polish colleagues have been busy in looking
at flat-fielding issues and the like, while Peter's replacement at Queen's
University, David Williams, is making progress in the analysis also. Our first
paper, basically on the instrument including the heliostat, was accepted for
publication in the European journal Solar Physics  and results have been
presented already at various conferences. I hope you will be seeing more and
exciting results from the SECIS data in the coming months. In the meantime have
a look at our SECIS web site and also my own personal one where there is a movie
of the August 11 eclipse images. The BBC eclipse web site also has features by
me and Peter Gallagher along with other eclipse chasers. See below for details.

SECIS web site: http://ast.star.rl.ac.uk/secis

KJHP's web site: http://ast.star.rl.ac.uk/kjhp/kjhp_page.html

If you have problems in displaying the movie, it can be obtained from David
Williams' ftp site at Queen's University Belfast: 
ftp://star.pst.qub.ac.uk/pub/drw2/sec_best.mpg

BBC web site: http://www.bbc.co.uk/eclipse/solar_detectives/

Figure Captions:

Fig. 1: SECIS image from the Evans coronagraph at National Solar
Observatory/Sacramento Peak (left) with corresponding images from the Yohkoh
X-ray satellite (middle) and the TRACE ultraviolet imaging satellite (right).

Fig. 2: The University of Wroclaw heliostat (mirror not in place). The heliostat
can operate at any latitude and tracks the Sun at precisely the solar rate of
motion across the sky to form a horizontal beam of sunlight. The mirror (by
Zeiss Corporation) is flat to 1/10th wave and made of low-expansion glass.  

Fig. 3: (centre) SECIS image (one of 12728), white-light channel (views coronal
structures and prominences) compared with images from the EIT instrument on the
SOHO satellite (left in He II light, showing chromosphere and prominences; right
in Fe XII light, showing corona). 

				--ooOOoo--