K.J.H. Phillips
Space Science and Technology Dept., CLRC Rutherford Appleton Laboratory, Oxon., U.K.

A total solar eclipse is perhaps the most wonderful sight Nature affords to us here on Earth. Very few people get the opportunity to see this remarkable phenomenon in a lifetime since the band on the Earth’s surface within which a total eclipse is visible is usually so narrow that it is rarely passes through highly populated areas like cities or large towns. The 1999 eclipse, the last of the Second Millennium, was an extraordinary exception – the path of totality passed right through some of the most densely populated areas of the world, namely Europe, the middle East and the Indian subcontinent. Unfortunately, western European weather being what it is, not many people were able to view the eclipse from locations west of Romania, but those who gathered at the little seaside town of Shabla, on the Black Sea coast of Bulgaria, were rewarded with a spectacular view in weather conditions that can only be described as near-perfect – cloudless, windless, and a highly transparent atmosphere. This was indeed lucky in view of the fact that there was a violent thunderstorm just a few hours later that threatened to dampen the spirits of the conference delegates during the excellent entertainment to celebrate the occasion put on by our Bulgarian colleagues. The gathering at Shabla was a huge one, not only professional and amateur scientists but also sightseers from all over the world. They will have very vivid memories which they will treasure for many years.

Total solar eclipses are excellent opportunities to study a whole range of phenomena, so scientists are eager to catch these opportunities to make measurements or take photographs. One aspect is to study the Sun’s atmosphere that becomes visible as the Moon blots out the bright photosphere – something that has been done since the early eighteenth century at least, but which became very popular in the nineteenth century following a remarkable description of an annular eclipse by Francis Baily, a British astronomer who happens to have lived in my home town in England -- Thatcham, in Berkshire. The eclipse he observed, in 1836, was a near-total one where at mid-eclipse the Sun’s light turned into a mass of “Baily’s beads”, as they have become known as since then, round the Moon’s limb. The rest, as they say, is history. Great teams of astronomers have gone forth into the wild unknown to observe total eclipses, hoping to find yet more keys to the mystery of the Sun’s atmosphere. The incredible story of the French astronomer Pierre Janssen escaping Paris by balloon in 1870 to escape the siege the city was then experiencing is worth re-telling. He managed to get to northern Algeria, the site of the eclipse, with all his equipment, but his luck ran out as the skies were cloudy for the whole of the totality! I think this intrepid man deserves sainthood for his efforts. But there are many other aspects that people have studied in the past – not only astronomical but also biological (the effects of a sudden darkening and cooling on the animal kingdom) and meteorological (the response of the earth’s atmosphere to the swiftly passing Moon’s shadow).

Many of the astronomers and other scientists who were at Shabla – the class of ’99, we might call them – had a memorable reunion a year later to discuss their findings. The conference, held near the city of Varna, to the south of Shabla, was an opportunity to share the results from initial analyses and measurements. These Proceedings summarize the many papers presented. As can be seen, the range of topics is very wide indeed. I hope in this short account to summarize, or maybe more accurately make a short selection of, the principal results.

Our hosts at the 1999 eclipse and for the Varna conference were members of the Bulgarian Academy of Sciences in Sofia, and did a wonderful job in the very complex arrangements. First and foremost were Academician Dimitar Mishev and Professor Dr Vladimir Dermendjiev to whom I think everyone who came to Bulgaria from abroad must owe an enormous debt of gratitude. It is particularly poignant that so soon after the Varna conference Professor Dermendjiev suddenly and most unexpectedly died. I personally feel I did not thank him enough for the tremendous effort he undertook on behalf of my SECIS team in 1999 when we were anxiously awaiting the arrival of our equipment. Vladimir Dermendjiev was obviously an extremely popular figure in Bulgarian astronomy. I will always treasure the hour or so spent with him during the conference when he took me to a mass at the gigantic Orthodox Cathedral that dominates the city centre of Varna. He went to such lengths to explain all the ceremony and the architecture of the building and the paintings, then after the service was over he told me about his deep knowledge of and interest in historical astronomy. I was moved back then by the presence of this great man on that sunny September afternoon, but the significance of this memorable occasion seemed so much deeper when I learned to my shock and dismay of his death shortly after the new year, 2001. I am sure many of our Bulgarian colleagues who knew him so much better and for so much longer than I did will testify to his enormous charisma. Our sympathy must go to Vladimir’s wife and family whom I had the pleasure of meeting while we were all at Shabla.

The Local Organizing Committee and the secretarial help were very impressive in assembling all the conference delegates and making everything run smoothly. The conference was generously sponsored by the Evrika Foundation in Sofia which promotes the dissemination of scientific knowledge in Bulgaria. The Conference was opened by Academician Mishev and we were all honoured and delighted to have Professor Pantev, Governor of the City of Varna, address us and wish us well in our deliberations. It was pleasant to have recognition from a national television station and members of the press who were also present at the opening ceremony and who interviewed some of the delegates during the course of the week.

One of the principal reasons astronomers are interested in eclipses is still, after many years of study, the nature of the sun’s outer atmosphere or corona. One can observe the corona on any daylight occasion with the right atmospheric conditions using coronagraphs, but eclipses afford a much better view, especially of the corona beyond about 2 or 3 solar radii from the sun. The two papers which opened the conference, on the SECIS instrument, were about looking for fast modulations in the corona’s light with CCD cameras. Pawel Rudawy’s paper summarizes his study using Fourier techniques that seem to indicate the possible presence of such modulations, which would point to the presence of MHD waves and so implicate them in the heating process which has long eluded solar physicists. However, the modulations are not pervasive and our preliminary conclusions are that MHD waves, though they may play a role in the heating, are not the dominant heating mechanism.

During the 1998 eclipse visible in the Caribbean, Professor R. Gulyaev discovered a new component of coronal emission and he followed this up with successful observations from Shabla in 1999. The well-known K component results from Thomson scattering of photospheric light off free electrons, while the F corona corona is due to photospheric radiation scattered off circumsolar dust particles. A T component, observed in the infrared and resulting from the thermal emission emitted by dust particles heated by the sun, has been known for some years. Gulyaev’s discovery is of the so-called S component, which results from the sublimation of circumsolar dust particles and is evident in particularly the Ca II K line. Gulyaev not only confirmed his 1998 observations but also observed, in the interferograms which he describes in his papers in these Proceedings, the Ca II K emission from all over the sky. He attributes this interesting observation to dust from the Perseid meteor stream which by coincidence reached its maximum on the day of the 1999 eclipse, August 11.

The K corona, resulting from Thomson scattered radiation, is highly polarized, and observations over the years with both ground-based and space instruments have given us a clear picture of the nature of coronal structures. The group led by M. T. Ozkan which was based in Turkey during the 1999 eclipse have made interesting measurements of polarization with up to 50% amounts in the white-light corona, with the direction of polarization often following coronal structures like helmet streamers. The details are described in their paper. Their group also made several other observations, among which are observations of what they believe to be polar plumes though comparison with spacecraft data is needed to confirm this. V. I. Kulijanishvili from the Ambastumani Observatory in Georgia used his instrument to get similar polarization results and also temperatures and particle number densities for two coronal streamers assuming hydrostatic equilibrium. Ambastumani have had a long and distinguished history in the observation of solar eclipses, clocking up over an hour’s worth of coronal observations during a large number of eclipses in various parts of the world.

The Ludendorf or ellipticity parameter is often used to characterize the shape of the corona during eclipses, using isophotes at various levels. Its value normally varies between zero and unity over the eleven-year solar activity cycle. The observations by N. Petrov and colleagues and V. I.. Kulijanishvili confirm a very small or even negative value, which is what is generally seen near solar maximum. The shape of the 1999 corona seems to have been influenced by the presence of high-latitude helmet structures.

As even naked-eye observers will have been aware, the 1999 eclipsed sun was remarkable for the number of bright prominences visible. The paper by J. Kokotanekova et al. in these Proceedings is a description of the twelve prominences these observers recorded with their photographic instruments, together with locations which are predominantly equatorial though two are high-latitude. The “suspended” prominence on the south-west limb was especially unusual. It was recorded in many photographs that Bulgarian amateur and professional observers displayed at the conference and incidentally is a feature of images from the Extreme-ultraviolet Imaging Telescope on the SOHO satellite. An hour after totality in Shabla, Serge Koutchmy and colleagues observing from Iran saw quite a different shape to the prominence. The paper by N. Popescu and colleagues from Romania (including C. Dumitrache) gives an account of the motion of this small but interesting prominence.

Eclipse predictions seem to be so precise it would seem that there is very little modifying needed of the various ephemeris parameters involved in making the calculations. Even so at every total eclipse there are attempts at finding the exact track of totality on the Earth’s surface or the timings of one or more of the four contacts between the Sun and Moon. Two papers (by Popescu et al. and Werner et al.) describe such measurements.

The People’s Observatory at Stara Zagora in Bulgaria spent a lot of effort and time organizing preparations for the 1999 eclipse, and as a consequence a large number of observers were involved in a varied programme. A summary is provided by A. Stoev, but individual contributions also included here give more details. Some of these are meteorological, and concern the microclimate that is formed as the Moon’s shadow races across the Earth. It was fortunate for some of us with delicate instruments that the slight breeze that was blowing before and after the eclipse died down completely during totality. This effect is quantified by extensive measurements taken by the Stara Zagora group (see also the paper by Ivancheva et al. on radiation changes during the eclipse). Other contributions by this group were biological – there is a fascinating tale of the behaviour of bats that live in coastal caves that is well worth reading. Humans too seem to have a response that is difficult to understand (articles by A. Stoev et al. and I. Stoilova et al.). Measurements done by other groups (papers by Miloslavov et al. and Mardirossian et al.) do not show significant changes in either gamma-ray background levels or in geomagnetic and seismic parameters during the eclipse.