SOLAR and LUNAR ECLIPSES : Part 4
MY SOLAR ECLIPSE EXPEDITIONS
The adventure in trying to get to observe any solar eclipse is just as exciting as seeing the eclipse itself! As such eclipses occur very infrequently at any fixed location throughout the world, so you would have to be very lucky if the eclipse path to travel your rooftop or city, and sometimes even your country. Solar eclipses average about eighteen months between them, and this means that the eclipse chaser will have to travel to some exotic locality — often using their precious annual holidays. Frequently this will takes you places that you never have dreamed of going; nor ever found in some glossy travel brochure. So just going to any total solar eclipse is only one part of the real opportunities for even the most casual of amateur astronomers. Yet unlike most holidays or vacations, when you have the luxury of choosing the place and time you want to go, the solar eclipse determines exactly the time and place to be there. Even actually seeing the eclipse is not guaranteed. Often the weather may intervene, so it may be cloudy or raining on the day. Worst is that if you arrive late for some reason or another, the eclipse just does not wait for you. However, if you do see one — you will absolutely remember seeing the eclipse for the rest of your life!
Usually the choice of place within the path is the centre line of totality to gaining the maximum possible time of eclipse darkness. To find where you have to be on the centre line is the tricky part, becoming the same problem for everyone. It is much better to have your accommodation, at, or very near where you want to see the eclipse nearby. Some people the location is even more critical. For example, I have been involved in the Bailey’s Beads Experiment expeditions during the 1980s and 1990s. The accurately known place of the observer is very critical including your precise latitude and longitude and importantly is being able to identify it on some map. Yet even this places several limitations on travel and location based on the extreme limits of totality. Trying to achieve this is often just where the adventure starts.
Over the years some twenty Australian observers have conducted an experiment to observing Baily’s Beads during eclipses throughout the world. Francis Bailey (1774-1844) lived was first noticed bright spots on the lunar limb. These were later named beads, being the sunlight shining along the slithered arc along the edge of the line of the moon. They only are seen just before and after totality, and Bailey thought that these could be of scientific use. Bailey was first to deliberately observed this event at an annular eclipse, but subsequently observed this at the next total solar eclipse from Scotland on the 15th May 1836, and again from Italy in 1842. It is the rough edge of the Moon produces the beads such that sunlight shines through the valleys on the lunar surface. The relevance of the location within the eclipse path is that it determines the number of beads that will be seen and described. Although Bailey was not the true discoverer of the bead phenomena, his description of the event itself was so entrancing and thrilling, that he sparked general ripples of interest in the phenomena of solar eclipses; and something which continues day.
Those on the very central line of the path will see only the two beads and these occur at 2nd and 3rd contact — the times when the solar eclipse starts and finishes. Observers will see this twice — being the renown and spectacular Diamond Ring. Both of these contact points will be exactly 180 degrees apart. By moving north or south changes the position of points of contact, until either at the very northern or southern limit there can be only one visible theoretical ‘solo’ bead — setting the true edges of totality. We find that the number of beads near the limits should be the same regardless of your position in the path. The rough lunar terrain produces the so-called Watts profile, makes significant difference in bead production and where and when the beads will be seen.
It is also depend on the slope of the arc of the Moon against the solar disk. The general idea is to decrease the velocity of the beads along the arced-disk as they occur increasing the chances of seeing and recording more of them onto audio tape.
Also the closer you are to the eclipse path limits the more time you have to see and record them. Closer to the centre-line, both contact points in the final stages exhibits too many beads at once along the disk. These cannot be described because the curved arc produced by the Sun and Moon moves much too fast. To see beads properly, some compromise has to be made. So to see more beads you have to sacrificing some of the precious totality.
Living on the edge of the eclipse path allows more beads to be observed. More often than not usually some twenty-five to fifty are expected. My observations in New Guinea on 22nd November 1984 found an amazing 104 timed events. At that time I was merely 175 metres from the northern limit! More difficulties can arise at the extreme limits, in fact the real possibility exists to miss the event completely! As the eclipse path is not exactly known and it is possible for shifts up to 0.8 to 1.2 kilometres — hence at this theoretical place could be risky if you were foolish enough to be there. It position area could be named the Suicide Point due to the dire consequences of missing totality all together. I have strong desires to be within this area mainly because the events are really very exciting and has things that cannot be seen at the centre line. However, I have gain an even newer goal since this wonderful eclipse — I would like to photograph the transition between the light intensity of sunlight to darkness which I glimpsed on the hillsides in 1984. In Banka Island, this was my intent, but was near impossible because of the difficulty getting to the assigned site locations.
With an element of risk, and fairly close to the actual truth, as sung in song “Danger Zone” by Kenny Loggins, from the 80’s movie Top Gun;
“Living on the
So why measure beads of light? The primary purpose is that the solar diameter can be measured with a high degree of accuracy. After saying this, the most common question I get is why can we not measure this directly?
The artist or painter knows the reason. This is that the light falling on some shape darkens significantly towards the edges. In astronomy, the stars and the sun similarly exhibit this phenomena, which is termed limb-darkening. For hot bodies this is correlated with the effective temperature of the object. For our Sun, these effects our estimations of physical diameters — effects that are impossible to predict for the sun because of various incalculable effects. First ever to produce observations of this phenomena was Bailey in the 18th Century, and he also used his results to determine the solar diameter. For many years, the technique was not used again, and the Bailey’s bead turn out only to be an idle curiosity. However, subsequent observations during the 1970’s found that the diameter seemed much less, inferring that the diameter appears to be shrinking. Consequences of such changes might explain the climatic changes seen Earth. In the mid-1980’s, the now late Dr. Alan Fiala of the U.S. Naval Observatory in Washington, D.C. combined with the advanced amateur David Herald of the Canberra Astronomical Society started to organise expeditions to measure the solar diameter using Baily’s beads. They appealed to the amateur community where several Australian amateurs took up the challenge — including me. All these observations over the years have proved the value of such experiments.
The Solar Eclipse of 18th March 1988
The night prior to an eclipse can be difficult and rather torturous due to the fact that the excitement usually gets you first and sleep becomes just a chore. This night was no exception. I had to go to bed early as our adventure to the eclipse site was a horrid 1.00 a.m. in the morning. My mind thought of all the problems that could occur, and worse of all I had not even seen my site (if I was to get there at all).
Eventually sleep fell upon me, when no sooner than fleeting moments had past my small alarm on my watch sounded in the darkness. I dwelt for moments then my mind flashed instantly — Eclipse Morning. At almost the same time my room companion, Rob McNaught (Mr Supernova and since 2007, Mr Comet), told me to get up and go. A few more moments I was up, getting dressed and checking my gear. Out the door with my suitcase (minus the clothes) and to the lobby of the ‘Country Club’ where we were staying. I don’t remember being too enthusiastic about breakfast, but I did gulp two cups of coffee to motivate me ever-onwards.
We had organised a four wheel drive vehicle, and David Herald and his first wife Ann were ready to go, though both his two children, Aaron and Judith, were not so excited because of the time in the morning. The 4WD was already packed upwith all the essential provisions and equipment. Both kids were on one seat in the back, me sitting length wise on the opposite one with my back to the driver. Cramped together we set off to the eclipse site, wherever that may be. The dirt roads were gruesome and all the back seat passengers were very aware of it! I was grimly holding on to the bags, while the kids attempted to sleep. Several times I had to protect their heads from bumping into the walls of the 4WD. During this time and I talked to David about eclipse sites and he contingency plans for the southern limit.
The adventure stakes for the journey were raised some what in an attempt to get to the south side of Banka Island a task that made us a little apprehensive. Our previous attempt the day before was thwarted by the 400 metre long bog. We were going to attempt again at 2.00 am. in the morning — and this was only one of three bogs which we had to circumvent! A line of fifteen vehicles, trucks and buses, etc., were ahead of us. The driver got out and discussed our dilemma and asked if we could try to negotiate the bog before them because usually, you were supposed to wait your turn! They all kindly said in Indonesian something like “sure, go ahead”. However, they said, there was a vehicle stuck about half-way, and you have to work that out when you got there. So to the head of the queue we went, and after a momentary pause in the depths we went. The vehicle descended about 1.5 to 2 metres into the muddy long channel. Mud flung in all directions, even leaving a deposit of mud on the roof! In the dark sitting backwards all I could see was the wall of mud left and right, and pitch black behind. We reached the broken down old truck in the middle of this bog. The driver attempted to drive into the 1.5 metre wall of mud. “No, No, No, No!” quickly muttered the driver. There was no way past. Quickly, not wanting to get trapped himself, he transferred the drive into reverse and he backed out of the bog in the pitch darkness (the lights, too, now totally covered in mud). This is where I imagined attempting to walk out of the bog my own two feet. This was all too much excitement for one night, and if it wasn’t for the eclipse, I would have gone home there and then in disgust!
Back on solid ground again, David Herald and the quickly discussed the dilemma now facing us. This blow to get further south was almost fatal for our plans, having no way to travel to our expected sites. At best, we could only get half-way to the southern limit. Quickly we made the instant choice to try to make it to a place best called Tandijung Berikat, where no roads exist on my map! Back to the mining camp of Koba, and then to travel west to another camp near Lubuk-Besar. By now it was 3.15am in the morning and less than four hours to go. After taking new directions, and in wonderful starry skies, mind you, we arrived at the camp. The driver got out and awoke the mining camp director no less. He told us of the road to the location some thirty kilometres away but that we might find that some of the bridges might be down. Nothing to lose, so off we went again. After negotiation little more than a track and one or two bridges in some degree of disrepair we arrived at a spectacular point of land, with a lighthouse and a beautiful beach. It was now 6.00am in the morning. Dawn came quickly in the tropics, and the eastern horizon brightened spectacularly — including a island with palm trees. Paradise indeed!
David quickly discussed the class="qa">“so concentrate on the south ones!” He left my bag of telescope equipment case to set up then went off to another site some 150 metres further up the beach. I was finally alone. I had to set up very quickly as it was already three-quarters of an hour since we had arrived. Preparation then fell in a heap, and I tried to set up quickly. Nothing seemed to work. As the shadow marched across the Sun frustration turned to annoyance. More badly prepared than I wanted to be, I it set up the recorders and off I went.
Dave Herald’s daughter Judith approached me wanting to observe the eclipse with me. I unfortunately barked at her, and she returned to her father. I regretted this more than the events that followed, as I would have enjoyed ‘young eyes’ at the first eclipse she had seen. However, the stress and lack of sleep did not help.
Nevertheless, the clock marched on, and now it was ten minutes to go. Being set up as best I could, I scrutinised the edge of the limb for the first sign of beads. My mind wished to be somewhere else, and I cursed my poor preparation. If the eclipse was yesterday or tomorrow, I know I would be more confident, I ebbed into dismay, as if waiting for the electric chair to zap me and for me to die.
Then it was on for young and old. At 07h 26m local time I saw visually a rainbow arcing around the Sun, a quick photo, and back to the projection screen of my 50mm. f/12 refractor (now veteran of ten solar eclipses — two without me.)
The crescent then rapidly thinned. By 7h 28m 44s.91 saw my first southern bead, ten seconds were posted, and then another. A whole forty-five seconds lapsed and then I saw another. In quickening steps, then beads started all over the place. Some to the south then north or even at the same time. Nineteen events, then a quick breath, and the race was on again. My pulse quickens and the adrenalin again activates in my system. After the 69th event, I saw the chromosphere, four or five smallish beads and then second contact occurred at 07h 32m.
At last totality! You hear the exclamation on the tape,“Oh, my God!” Three prominences could be seen with the naked eye. One shaped like a ‘honey-pot’ or even one on top of the other! Both eyes and mouth were wide open. Quickly I looked around, then turning the projected eyepiece and looked shocked through the telescope at the stupendous sight. Structure in the corona, then the image was gone. I had knocked over the tripod. Profanities rain supreme. “How could you be so stupid”, I exclaimed. I wasted nearly thirty seconds correcting it.
Just like that, ½ one-and-a-half minutes were gone, and I realised that I must take some photographed. I looked through the camera eyepiece of the 400mm. telephoto. Quick adjustments, then, click, click, click. The Sun was going to come back, I could see the chromosphere. Click, click, then third Contact came back, two minutes and three seconds had past. My last eclipse was eight seconds, and I did less!
My plans had come to zero, and I cursed as I attempted to adjust the tripod. By 07h 34m, I had returned to some normality, and observed another twelve beads, and by the 37th minute, no more beads were seen. Depressed, (you can hear it on my tape) I cursed my own stupidity.
Judith then came along and talked to me on what she had seen in pure excitement, which made me slightly happier. Fifteen minutes later David Herald came along, with a big grin from ‘ear to ear’. I told him of my misadventure, but I had recorded eight-four events! He was apprehensive though because of the calculation involved in the usefulness of the results we obtained — months of painstaking calculation work still lay ahead for him.
Our thoughts then told of what we had seen, and we discussed the events in some detail. I packed up my case and then loaded, the three hour trip in the back seat to Koba. I cursed for most of it, but some enthusiasms remained to find out how the others went. In the mining camp’s dining room by 11.00 a.m. we sat and gossiped busily for an hour or so. I celebrated with three full glasses of my favourite alcoholic drink, the wee Scottish liqueur Drambuie and went and had my well deserved long sleep. We relaxed the remainder of the trip and each brought his or her memories of an excellent and successful eclipse expedition!
Last Update : 26th November 2012