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Journal

No. 50 - November 2006

The March 29 eclipse from Libya

The solar eclipse of 2006 March 29 was total along a band that stretched from the NE coast of Brazil, across N Africa to Turkey and onwards through Asia to end in N Mongolia. Anyone viewing the event from Britain experienced only a shallow partial eclipse, with only the southern 20 % of the Sun's diameter hidden by the Moon at mid eclipse as seen from Edinburgh.

Like many in the UK, my first experience of a total solar eclipse came with the one on 1999 August 11. Unlike many in the UK, though, I chose not to risk the uncertain, and ultimately largely leaden, skies of Cornwall. Instead, I noticed that Edinburgh had a direct air link to Varna in Bulgaria, close to the centre line of the eclipse where it crossed the Black Sea and where the weather prospects were rather better. A holiday was duly arranged at the resort of Albena, and my wife Gillian and I, with our two (then) teenage offspring, enjoyed a superb view of totality with the Sun high in a cloudless sky.

I had never thought of myself as being afflicted by an eclipse-chasing bug, but something of the sort must have struck about then. The same seems to have happened to my good friend, Russell Eberst, a colleague at the Royal Observatory and a fellow satellite-enthusiast. Russell, together with his wife Margaret, had been frustrated by the Cornish experience, so we resolved to take a more active interest in forthcoming eclipses. That is how we found ourselves, with Gillian and Margaret, in an Orkney field in the early hours of 2003 May 11 in the hope of catching the annular solar eclipse at dawn. Sadly, all we saw was cloud, though the piper, the band and the bar helped the event go with a swing.

The Pickups and Ebersts share rather more than this interest in eclipses. Coincidentally, we have the same wedding anniversary and, remarkably, both Gillian and Margaret have the same birthday. The fact that this is March 29, the date of this year's eclipse, reinforced our determination to make the most of it, but this didn't stop Russell and Margaret tripping off to Madrid to catch the annular eclipse last October 3.

The March 29 eclipse was attractive for other reasons. For one thing, it had the longest duration of totality of any total eclipse between 2001 June 21 and 2009 July 22. In addition, land based observing sites with good prospects of clear weather were quite easily accessible from Europe. Our Google map of its track plots the point of longest eclipse, 4 minutes 7 seconds, just as the Moon's shadow enters Libya from Chad. By the time the umbra reaches the coast of Turkey observers could still expect a respectable 3 minutes and 45 seconds of totality.

Turkey, in fact, was probably the most popular destination for eclipse-chasers. Although the weather prospects were more uncertain than locations south of the N African coast, Turkey already had a thriving tourist industry, with many "eclipse packages" available and I expect that a number of ASE members took advantage. In the end, Turkey provided clear skies and a superb view of the spectacle. Horst Meyerdierks, for example, returned with several excellent photos of the event from his observing site on the southern Turkish coast and the BBC's Sky at Night cameras could not have been far away.

eclipse track
The track of the March 29 eclipse.

The Pickup-Eberst quartet, though, pushed the boat out, almost literally. We booked a cruise through Explorers (http://www.explorers.co.uk) that included a stopover in Benghazi with a journey inland to a chosen observation site in the Libyan Desert south of the Jalu Oasis. The cruise aboard the MV Perla also took in the ancient Minoan site of Knossos in Crete, linked to the myths of the Labyrinth and the Minotaur, as well as the Greek ruins of Cyrene E of Benghazi and the World Heritage site of Leptis Magna, the well-preserved Roman city near Tripoli. We also called at Santorini and, finally, Athens.

It became clear after we docked at Benghazi that the Libyan authorities were a little unaccustomed to, and uncomfortable with, the prospect of 700-plus foreigners trooping off the view Cyrene on March 28, the day before the eclipse. A trip that might have taken only a couple of hours each way, took twice as long, largely because our buses were required to travel in convoy, and to be escorted within the city limits of Benghazi. Also, if any bus needed a refuelling stop, then the whole convoy ground to a halt. The lessons learned on that day caused a rethink of our schedule for Eclipse Day, with our departure for the observing location brought forward by several hours.

As it was, the journey of some 500 km S from Benghazi took nine hours, which felt even longer for most of us since few of our 20 (or so) buses had working toilets. In various states of discomfort, then, we made it to our eclipse vantage point with only minutes to spare before first contact, the moment when the Moon's disk began to nibble away at the Sun's edge. Fortunately, we had been within the total eclipse track for the final few hours of our journey as we encountered more and more traffic along the well-made, and normally very quiet, roads into that part of the Sahara. The scenery was of flat sandy desert, with occasional distant views of the smoke and flaring stacks of the Libyan oil industry for which, probably, the roads were constructed in the first place. Increasingly, though, the desert was peppered with the vehicles, tents, vans and telescopes of eclipse watchers from all parts of the world. The only camels we saw were sitting smugly in the back of a passing truck.

In fact the place where we piled out of our buses fell a couple of kilometres short of our target destination, an encampment that the Libyans had built for the day and dubbed Eclipse City. Here were food, drink and toilets, but also more activity and wind-blown dust to the extent that we were probably better off where we were. We did call there after the eclipse, collecting, among other things, our free eclipse T-shirts.

For the anoraks among you, our actual observing site (plotted on our Google map) was at latitude 28 degrees 14.6 minutes N, longitude 21 degrees 31.0 minutes E, which placed us just 1.93 km S of the central line of the eclipse. There we enjoyed (to put it mildly!) 4 minutes 3 seconds of totality between 10:26:38 and 10:30:41 UTC, with the Sun 65 degrees high against a cloudless sky.

Our chosen observing equipment was limited to binoculars and our naked eyes. We are not astrophotographers, and suspected that anything we could produce would be outshone many times over by others around us. Also, my experience in Bulgaria suggested that there was more than enough to see and absorb without worrying about forgetting to remove the camera lens cap or, as in one sad report we heard after we returned to the ship, experiencing a camera memory card declaring "I'm full" just as totality got underway.

awaiting totality
The author awaiting totality.

I did ensure, though, that I had a pair of tripod-mounted binoculars, with a shade and screen to allow a reasonably sized projection of the Sun's disk. This proved a popular choice for it allowed many more people to follow and view the progress of the eclipse than was possible using properly filtered (of course) cameras or spotting scopes. It was also quick to set up and the image scale was such that we were able to confirm first contact within seconds of the expected time.

We drew a steady stream of visitors to our little outpost, many of them enthusiastic and friendly Libyan nationals eager to record the progress of the eclipse using their mobile phone cameras and, no doubt, transmit the pictures to their less fortunate friends. Something we did notice was that, Libya being a Muslim country, from time to time during the partial phase there were several long rows of men in different parts of the desert all paying homage in the direction of Mecca, though it was also obvious that there was no universal agreement about what direction that should be.

For most of the 78 minutes between first contact and the beginning of totality at second contact, the gradual fading of the light could almost pass unnoticed, presumably because the eye is so good at adjusting to the changing level. It was interesting, though, to judge the visibility of the planet Venus which was shining at magnitude -4.3 in the SW and rather lower than the Sun at the time. Soon after first contact, Venus was just visible to the unaided eye, but took some finding. Fifteen minutes before totality, it was obvious to anyone who glanced in that direction. By then, too, the shadows had become much sharper than normal because the E-W extent of the visible Sun was down to only 6 arc minutes from its usual 30 arc minutes. It was also about this time that changes in the micro climate ahead of the Moon's shadow generated a few stronger gusts of wind along with a few passing clouds, the latter probably of dust. Otherwise, there was only a light wind flowing across the site from the SW.

As excitement built towards second contact, my attention was on the diminishing arc of projected sunlight on my screen. Suddenly, the cry of "shadow bands" echoed around the desert which became alive with dancing bands of light and shade. To my eyes, they appeared as a multitude of fleeting torpedo-shaped ovals, a metre or two long in a N-S direction and tending to drift slowly to the NW, in the same direction and at about the same speed as the wind. The explanation appears to be that cells of different density in the atmosphere acted like lenses to refract the final slender rays of sunlight so that they sometimes augment, and sometimes detract from, the flux of light reaching any point on the ground. As the cells drift in the wind, so do the shadow bands. The mechanism is probably very similar to that which causes stars to twinkle at night.

I suspect that the shadow band phenomenon lasted for 30 seconds or more, though I missed its beginning and soon turned my attention back to my projection as mountains on the Moon's limb broke up the final sliver of the Sun's photosphere into a chain of points, the phenomenon of Bailey's Beads. As these disappeared, totality began, cheers rang out from all around, and it was time to turn a second pair of binoculars sunwards. The corona was immediately obvious, reaching out in streamers to E and W of the disk. With the Sun now approaching the minimum in its 11-years solar cycle, this was much as expected, signalling that the Sun's overall magnetic field is now less disturbed than that near solar maximum. Also obvious at first glance was a crimson prominence near the 10 o'clock position which (probably no coincidence) seemed to sit at the base of the longest coronal streamer. Spikes radiated outwards from the Sun's polar regions, reminding me of iron filings near a magnet in those long-ago physics experiments at school.

To the naked eye, the spectacle was awe-inspiring. The corona seemed to extend for several times the Sun/Moon's diameter, further than in most photographs I have seen, with the Moon's disk appearing as a stunning jet-black gem at its heart. The sky all around was dark like a deep twilight, but the lower few degrees in all directions was a much brighter red-to-yellow hue as we looked beyond the umbral shadow. After my experience in Bulgaria, I was not surprised that no stars were obvious in the eclipse sky. Venus was unmistakable, though, and I could make out Mercury (magnitude 0.9) with my naked eyes about halfway between Venus and the Sun. Forming an equilateral triangle with Mercury and Venus was Fomalhaut at magnitude 1.2, but this I failed to see. Russell saw both Mercury and Fomalhaut, but only through binoculars.

diamond ring and corona
Left: Third contact and the terminal diamond ring imaged by Dr Peter Morgan, a fellow eclipse chaser from Bradford.
Right: The corona. A montage of images with exposure times ranging from 1/1000 to 1/4 second, each unsharp masked. By ASE's own Horst Meyerdierks.

As the eclipse progressed and the Moon's disk drifted E in front of the Sun, the 10 o'clock prominence was obscured and several lesser prominences became visible above the Sun's W limb, each at the base of another coronal streamer. All too soon third contact was upon us as direct sunlight flashed into view through a couple of valleys, the double diamond ring effect soon giving way to a single dazzling diamond that drew gasps and more cheers. Over the following seconds, the corona faded and I tried (but failed miserably) to grab a decent photograph of the Moon's shadow as it raced away to the NE. Euphoria got the better of common sense in another way, and I neglected to check again for those shadow bands for which I, for one, will always remember this eclipse.

I have to admit, that we did not linger on the sand until fourth contact, but rather packed up and embarked on a (successful) hunt for a bus for our return trip, one with a functioning toilet! The talk on our long journey back to our ship in Benghazi, and for days afterwards, was of the experience we'd shared and the prospects of doing it all again at the next favourable eclipse, perhaps in the Gobi Desert in China in 2008. Oh, and Gillian and Margaret had a really happy birthday.

Incidentally, there were several enthusiasts from the BAA, the British Astronomical Association, among our shipmates, and the BAA is planning to produce a DVD with images and movies taken during the eclipse. Details at http://britastro.org/baa/content/view/82/2/.

Alan Pickup


Contents

Cover page

Presidential news

The March 29 eclipse from Libya

Let there be rock - The story of the Hambleton meteorite

Let there be rock - addendum

Brown dwarfs

About the ASE Journal


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