Obscured Splendour
A personal account of the total solar eclipse of 11
August 1999
by William Gould
(This article was written in September 1999.)
- Introductory background
- Once in a lifetime: The rarity of a total solar eclipse
- What we were expecting
- The mechanism of a solar eclipse
- Darkness on a summer morning: what we saw
- Conclusion
- References and links
Introductory background
Cornwall and Devon in high summer are among the UK's prime holiday destinations. Generally good weather with plenty of sunshine, fine beaches and excellent coastal walks draw in active people of all ages. Stately homes and museums cater to art and culture lovers, while seaside resorts, wildlife parks and amusement parks provide fun for all the family. In 1999, though, Cornwall and south Devon were set to attract an even greater number of sun-seekers – would-be witnesses of the great total eclipse of the Sun on 11 August.
Although those with a more than passing astronomical interest had booked their accommodation at least two years in advance, general interest in the eclipse seemed slow to rise. The full media hype did not get rolling properly until a few months before the event. The government sought to discourage people from directly observing the eclipse in the interests of preserving their eyesight (laudable, but somewhat ill-informed and over the top), and the local authorities feared a traffic deluge and, according to some, failed to put their backs into promoting the area as an "eclipse venue." There was some remarkable misinformation given out by officials. At Hope Cove, south Devon, near where I stayed to experience the event, the coastguard told people that when the eclipse started, it would go dark for two hours!
At the start of August, with the eclipse just days away, those offering accommodation complained that they still had places to spare. Some people were evidently offering rooms and camping sites at grossly inflated prices and got few takers. Glastonbury-type pop and new age music festivals proliferated and probably saturated the market for that sort of thing. In the event, far fewer people turned up for these fringe events than had been expected, and a lot of money was lost. But on eclipse day, there were a lot of people who just made a day trip to the southwest to witness the phenomenon, and within minutes of the end of totality, traffic jammed the roads out of Devon and Cornwall.
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Once in a lifetime: The rarity of a total solar eclipse
Everyone realized the rarity of the eclipse, the media saw to that. There had not been a total solar eclipse visible from anywhere in the UK for 72 years. Footage was unearthed of the last one, which had been seen in North Wales and northern England in June 1927. It got plenty of screenings. Press and advertisers hailed the August 1999 event as "the last total solar eclipse of the millennium!" The rarity factor was actually a significant issue: the UK would not see another total eclipse of the Sun until 2090.
This fact, despite being true, rather obscures another one: that total eclipses are not in themselves particularly rare. In any year there are on average two or three solar eclipses; the maximum is five. Most are partial eclipses, with the Moon hiding only part of the Sun's dazzling photosphere (central disc). But over a period of eighteen months to two years, there is likely to be at least one total solar eclipse visible somewhere in the world. In such an event, the black disc of the Moon would entirely cover the photosphere, allowing a glimpse of features normally swamped by the Sun's glare – its inner atmosphere, or chromosphere, and its faint, rarefied outer atmosphere, the beautiful corona.
The operative phrase is "somewhere in the world." What makes total eclipses seem uncommon is the fact that they only ever occur on that very narrow region of the Earth upon which the inner cone of the Moon's shadow falls. As the Moon moves, its shadow traces out a narrow track over the Earth's surface. This track is called the path of totality.
This map shows the paths of totality for recent and upcoming eclipses. Their narrowness shows that you have to be in the right place at the right time to see a total eclipse.
Only the places on the direct line of the path of totality will experience the total eclipse. Because of the Moon's complicated motion about the Earth, successive total eclipses take different paths of totality, in most cases over the sea. Given such limitations, it's perhaps not surprising that we hail eclipses as once-in-a-lifetime events. When they do happen, though, they offer us a chance to see one of nature's most beautiful spectacles. The 1999 eclipse promised to be just such a spectacle.
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What we were expecting
I had seen a couple of partial solar eclipses but I had only seen total ones on television and read descriptions of them in books. The August 1999 eclipse was to be my first "live" experience of the phenomenon. Eclipses occur because of a miracle of perspective. By a happy accident, the Sun, though 400 times bigger than the Moon, is also 400 times more distant from the Earth. So for an Earthbound observer, the discs of both the Sun and Moon appear about the same size. An eclipse happens when the Moon in its orbit moves in front of the Sun and cuts off part or all of the light from its photosphere. From the time of "first contact," when the Moon begins its passage in front of the solar disc and the Sun appears to have had a "bite" taken out of it, a total eclipse gradually progresses through a partial phase during which the Sun is seen to diminish to a thin crescent. The sky gradually gets darker, and shadows on the ground become sharper. Hundreds of crescents of light appear under trees. As the Sun's light continues to fade, you may be lucky enough to see rippling shadow bands produced by the Earth's atmosphere. If you are standing on a hill or a clifftop overlooking the sea, you may see the shadow of the Moon rushing toward you out of the west at 2,000 kilometres an hour. Then, as the Sun's disc finally disappears behind the Moon's, there is a dazzling "diamond ring" effect.
Top: A London Times picture of the corona during the August 1999 eclipse. Note the pink-tinged chromosphere, the Sun's inner atmosphere on the left edge of the Moon's disc. At about seven o'clock on the disc there is a flame-like prominence visible. Bottom: This set of images taken a few minutes apart appeared in The Daily Telegraph of 12 August. It shows the stages leading to totality, from diamond ring to corona.
If conditions are right and clouds are absent, the sky becomes as dark as night. Mercury and Venus and some of the brightest stars may be visible. For a brief moment, the last rays of the disappearing Sun are fragmented by the Moon's mountains and valleys, producing an effect known as "Baily's beads" (in honour of Francis Baily, the 19th-century English astronomer who first described them). These points of light may ring the edge of the Moon's black disc, appearing like some circlet of tiny sparkling jewels in the dark sky. Then suddenly, as the eclipse enters totality, the pearly corona flashes into view. Its eerie light – about as bright as the full Moon – covers the scene. What look like flames may be seen to flare from behind the Moon's black disc. But these are not flames; they are prominences, vast strands of luminous hydrogen gas thousands of kilometres long erupting from the solar surface.
As the Moon moves on, the corona vanishes and the "diamond ring" returns. The eclipse re-enters its partial phase and the thin crescent of Sun reappears. More and more of the Sun's disc is gradually revealed. The whole process from first contact to last contact (when the Moon finally moves out of our line of sight to the Sun) may take about 2½ hours, with totality lasting for anything from a few seconds to several minutes.
That was the display that I hoped to
be seeing as my wife Tessa and I travelled down on 8 August to the Port Light
Hotel, Bolberry Down, just at the head of Bigbury Bay, northwest of the town
of Salcombe along the south coast of Devon. The Port Light, a former golf
club, had also in its day been a radar station for the RAF and was perfectly
sited for observing a solar eclipse, with uniterrupted views to the south. If
the sky stayed clear, the spectacle would be marvellous.
Although I had never had the resources to chase eclipses across the world like dedicated professional and amateur astronomers do, I had always been interested in them. This one had been at the back of my mind for about 40 years, ever since I had seen it listed in a table of future eclipses in a popular astronomy book I had as a child. Now, weather permitting, I was going to see it.
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The mechanism of a solar eclipse
As Tessa drove the car, I thought about the complexities of eclipse science. It takes a lot for nature to set up the perfect conditions for a total solar eclipse. But everything runs to a meticulous timetable, and if you can do the mathematics you can know exactly when an eclipse will occur and where to be to see it. The ancient Babylonians were among the first to be able to predict eclipses. They even worked out that eclipses of both Sun and Moon follow cycles. Each cycle lasts almost exactly 18 years and is called a saros. At the end of each saros, the Sun, Moon and Earth are in more or less the same positions relative to each other and the cycle of eclipses begins again in roughly the same terrestrial latitudes. These eclipse cycles are not repeated infinitely, however. Eventually, the universe moves on, and the relative positions of Sun, Moon, and Earth have changed too much. After 71 saros periods for the Sun and 48 for the Moon, a new cycle begins. Several cycles are in operation at any one time.
So much depends on the strangely complex movements of the Moon. The Moon travels around the Earth at an average distance of 384,500 kilometres. Its diameter is only a little more than a quarter as big as the Earth's. While the Earth's shadow extends 1.6 million kilometres into space, the Moon's only goes a quarter as far. The Moon's shadow in fact takes the form of two cones. The outer cone, or penumbra (half-shadow), has its apex facing toward the Sun (see the illustration), while the inner cone of dense shadow – the umbra – has its apex pointing away from the Sun.
A sketch of what happens in a total solar eclipse. This sketch is not to scale but it tries to give an idea of how the Moon's shadow is cast upon the Earth.
During a solar eclipse, the base of the penumbral cone forms an extensive "footprint" on the Earth's surface, within which some light from the Sun is visible and observers witness a partial eclipse. The penumbral "footprint" is several thousand kilometres in width. How much of the solar disc is obscured depends on how close the observer is to the region of the umbra. At total eclipse time, the apex of the umbra just reaches as far as the Earth to form a much smaller "footprint" on the Earth's surface inside the one produced by the penumbra. The footprint of the umbra is usually barely 300 kilometres wide; the one for the August 1999 eclipse was only 100 kilometres wide. Within the umbra, all light from the Sun's disk is cut off and any observer located there will see the eclipse as total. The umbra's footprint is therefore known as the zone of totality.
During a total solar eclipse, the Moon's shadow, moving at an average speed of about 35 kilometres a minute, tracks from west to east over the Earth's surface along the path of totality. The speed of the Moon's passage, plus the west-to-east rotation of the Earth, means that the total phase of any eclipse can last no more than 7.6 minutes. The maximum length of totality for the 1999 eclipse, seen over Romania, was a bit under 2½ minutes.
The narrow path of totality of the August 1999 eclipse across Europe. It travelled on over Iran and India. The footprint of the umbra on the Earth's surface was just 100 kilometres wide.
The picture of the Moon revolving around the Earth is a simple one for us all to grasp but is some way from describing the real situation. Actually, the Earth and the Moon have an unusual relationship. The Earth is 81 times as massive as the Moon and is very much the dominant partner, but the position of the Moon among natural satellites in the solar system is unusual. With the exception of Charon, the lone satellite of Pluto, the Sun's outermost planet, no other satellite – not even the huge planet-sized Ganymede or Titan – is as big in relation to its primary as the Moon is in relation to the Earth. As a result, the two bodies waltz around a common centre of gravity and orbit the Sun as a kind of double planet.
The Moon's path around the Earth is angled at just over 5° to the plane of the Earth's path around the Sun (seen edge-on in the above illustration). As viewed from the Earth, the plane of that path is defined by the apparent year-long passage of the Sun against the constellations of the zodiac. The great circle traced out by the Sun in this way is called the ecliptic. The Moon's orbit crosses the ecliptic (the Earth's orbital plane) at two points, the ascending node and the descending node. Eclipses can only occur when the Moon is at or very near one of these nodes during its "new" phase.
The Moon's distance from the Earth varies between 356,410 kilometres and 406,740 kilometres. The actual path or orbit that the Moon follows as seen from the Earth is set at an angle of 5° 9 ' to the plane of the Earth's orbit around the Sun. As seen from the orbiting Earth, the Sun appears to trace out a circular path against the background of the zodiac constellations. This path is called the ecliptic. The two points at which the Moon's orbit crosses the ecliptic (the Earth's orbital plane) are called the nodes. The gravitational pull of both Earth and Sun on the Moon causes the Moon's motion to be disturbed by numerous side-effects. One result of these disturbances is to cause the nodes to regress. In other words, it takes the Moon increasingly shorter time intervals to move from one node to the other and back again. Looking at the situation geometrically, the nodes of the lunar orbit physically move around it, completing one 360° revolution in 18.6 years.
Clearly a solar eclipse can only happen when the Moon lies between the Earth and the Sun. At this point in its orbit, the Moon is designated "new" by astronomers. Usually the three bodies do not line up because the new Moon is either above or below the Earth's orbital plane. This is why we don't get an eclipse every month. For the alignment to be accurate, the Moon has to be passing through or very close to the ecliptic while positioned between Earth and Sun. So eclipses can only ever happen when the Moon is both on the Sunlit side of the Earth and at or very near a node.
Most eclipses are partial because the alignment of Sun, Moon, and Earth is just slightly off, allowing only part of the penumbra to touch the Earth while the umbra passes it by completely. In such a case, the solar disc is only partly hidden. A type of eclipse called an annular eclipse occurs when the Moon is very distant from the Earth. In such an event, the umbra would fall upon the Earth but the apex of its cone cannot quite reach our planet . For those in line with the umbra's cone, the centre of the solar disc is hidden, leaving part of the photosphere visible as a dazzling "ring of fire" around the Moon's black disc. Conditions have to be just right for a total eclipse, and Earthbound watchers have to be in the right place at the right time.
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Darkness on a summer morning: what we saw of the 1999 eclipse
We feared a difficult car journey battling hordes of other eclipse-chasers to south Devon, but things turned out to be much easier than we had thought. Traffic ran quite smoothly, probably because it was a Sunday morning, and we arrived to a warm welcome at the Port Light. Our main concern was the good old British weather. After a hot and sunny July in southern England, August was already ushering in some worrying changes. While we and other would-be eclipse watchers were arriving from the east and north, a weak front was heading in over the Atlantic from the west. A week before eclipse day, the UK Met Office was forecasting a 60 per cent chance of clear skies over Devon and Cornwall for the eclipse. By Tuesday, 10 August, the eve of eclipse day, the chance had fallen to between 20 and 30 per cent. That Tuesday evening, the skies were cloudy, but there seemed to be enough breaks to allow us to be hopeful. There was a pinkish tinge to the sky that evening that reminded us of the old rhyme "Red sky at night, shepherds' delight."
We awoke at about 07:00 BST on Wednesday 11 August; the Sun was shining weakly through cloud, and we harboured some hopes. But over the next three hours the cloud cover increased. The Port Light's excellent location, with clear views over a couple of fields to the sea, was going to avail us nothing. Nevertheless, we and our fellow hotel guests joined crowds of other men, women and children in the hotel grounds looking toward the southern horizon. With so many people around, there was bound to be a party atmosphere. By the time of first contact (09:57 BST), the skies were fully overcast – "leaden," as Patrick Moore called them. For the next hour we saw nothing of the partial phase and knew in our hearts that the breathtaking spectacle of totality, about which I had learned so much, was going to be denied to us.
Close. but no corona. These murky images of a cloud-obscured Sun during the partial phase of the August 1999 eclipse were all that the photographer, Ian Cameron Smith, saw from Cornwall. The one on the left was taken at 10:55 BST, the other one eight minutes later. But the clouds came back to conceal the two minutes of totality that began at 11:11. From where we were in south Devon, we did not even glimpse the Sun until about half an hour after the Moon had completed its passage in front of it.
Over the hour after first contact, the sky must have darkened, but the effect was so gradual that our eyes adjusted to compensate for the process. By 11:00, though, we could see that the light level had dropped appreciably. The light became eerie in a way that is hard to describe. The cloudy skies appeared suffused with a pearly yellow colour. Totality for us in our location was set to arrive at 11:13. As that time approached, a deeper darkness seemed to gather on the western horizon. Suddenly, right on time, the Moon's shadow was upon us. Above us the sky was as dark as a cloudy night. The western and eastern horizons were ribbons of pale golden light, and some of this same light was scattered through the overcast sky. The temperature had dropped. Totality and the deep shadow of the Moon were sweeping over us. Everything went quiet, although we heard cheers from some of the boats on the sea. Our dog Holly was quiet too; sometimes, it is said, dogs howl during totality, but she didn't. I confess I was awe-struck at that moment and could not help thinking that, even though we humans had predicted this event, there was nothing we could do to stop or change it. Nature was doing its own thing, and we were irrelevant.
In less than two minutes, it was over. The shadow swept on to the eastern horizon and the still overcast sky lightened as if someone had turned up a dimmer switch. Totality was over at Bolberry Down. It would not be back this way again for 91 years.
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Conclusion
At 1 p.m., nearly half an hour after last contact, the Sun put in an appearance at last. As a bystander near me put it, nature was "taking the piss." Forty years of looking forward to seeing a special and rare natural event meant nothing in the great scheme of things. As people settled down to party for the rest of the day, Tessa and I had lunch and then walked with Holly down to Sawmill Cove, one of the local beaches. Life was getting back to normal, and we were left to ponder the experience we had been through.
In purely astronomical terms, the eclipse of August 1999 had been an unqualified disappointment for me. Although the media tried to "talk it up" as an experience of unparalleled excitement, I could not help feeling cheated. We had not been vouchsafed even a glimpse of the full effect. TV broadcasts showed wonderful views of the eclipse from an RAF Hercules flying above the cloud over Cornwall at an altitude of 10,050 metres, but it wasn't the same. News bulletins later showed the views people got in Romania and Turkey. I was envious. I still am. It makes me feel that I should save my pennies and try to get to southern Africa for the next one in 2001, or even Australia in 2003. But could I face such a disappointment again?
But if I am honest I did take something away from the eclipse experience. I may have missed the full glory of a total eclipse on this occasion, but the actual experience of the atmosphere and the awe and sheer helplessness I felt at the moment of totality do remain in my memory. Cloud may have obscured the splendour I wanted to see, but I, like thousands of others on that August day in England's extreme southwest, had been touched by the Moon's dark umbra. It was a privilege to be there.
References and links
With the exception of three illustrations that I did myself, the images used in this article come from other sources and some are copyright.
The Times and Telegraph pictures are from the Internet editions of those newspapers for 12 August 1999. Register online with The Times and The Daily Telegraph
The map showing the paths of totality for eclipses from 1996 to 2020 is adapted from the one at rainbowsymphony.com. (Note: This link is no longer acvtive – WG May 2007).
The map showing the extent of the August 1999 total eclipse is based on one by Fred Espenak. You can find it at his Eclipse Homepage.
The excellent map showing the path of the eclipse across Europe comes from a site that I cannot find at present. I shall post the link if and when I come across it again.
The two photos by Ian Cameron Smith come from his eclipse site at www.hermit.org.
In addition to these fine resources there are a host of eclipse sites still operating as of 8 September 1999. You can find them at The UK Eclipse Group. This is the essential site, which mixes the popular with the scientific. Its comprehensive list of links needs no duplication from me.
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