GCSE Astronomy

Solar Eclipse in Portsmouth, August 1999

As I write this, in 1998, how many people are aware of the forthcoming solar eclipse of Wednesday August 11. 1999 , the first in this country since 1927 and 98% total from Portsmouth. Indications from the interest in Hale-Bopp, and indeed from the intense interest aroused in 1927, point to enormous enthusiasm by the time the eclipse actually occurs. And in 1927 the total eclipse only lasted for 20 seconds - this time it will be 2 minutes.

Added to that, the eclipse is the first in Europe since 1961 (if we exclude one restricted to Finland in 1990) and will be the last one anywhere in the world this century. Europe will have to wait until 2081 for the next one, and Britain the 23. September 2090, again in Southern England.

The eclipse will be total in most of Cornwall (and South Devon) where apparently accommodation is already scarce and doubts are being expressed about how the county is going to lever in all the extra visitors on top of the normal holiday influx.

It will be necessary to be within about 10 kms either side of the center of the 80km. wide path of totality to see the total eclipse for the full two minutes. Elsewhere it will be less e.g. in Torquay, one of the last places on the British mainland to see the total eclipse, it will last for about one minute. Roughly speaking, the farther you go into Cornwall, the nearer you get to the center of totality.

During discussions with a colleague from the Open University, Dr. Barrie Jones, veteran of several eclipses, he has informed me that a total eclipse is a totally different experience from a 98% eclipse, so you would be missing out on something by observing it from Portsmouth.

Unfortunately, Cornwall has another problem apart from over-crowding - its street lights will come on automatically (it s too expensive to shut them all off), affecting the seeing if you are near a built-up area. Obviously this streetlight effect will be even more unfortunate from an area like Portsmouth.

There are alternatives. The Royal Astronomical Society is holding a special gathering in Alderney although this will presumably suffer similar problems to Cornwall. Much better for people from Portsmouth might be to pick somewhere along the path of totality in Normandy and Northern France , the eclipse will be seen in Cherbourg and Le Havre, passes about 20kms. north of Paris, and then thru Reims, Metz and Luxemburg town. Having said that, if you have access to a boat of some description, the Channel south of the Isle of Wight might be a good vantage point away from the streetlights (although I am latterly lead to believe that "freak" weather conditions might occur around eclipse time, so be careful. Especially in view of the great strain that the emergency services will be under - there will be a HELL OF A LOT of small boats out in the Channel on that day).

A bit further away, the path will pass thru both Stuttgart and Munchen, although here you are going to have to presumably steer clear of the lights from the big cities. From there the path goes thru Austria (south of Vienna), Hungary (south of Budapest) and Romania passing thru Timisoara and the capital Bucharest. It then heads off thru Turkey and across Asia to the Bay of Bengal.

The overall message is that, if you fancy going, anywhere, you ought to think about booking now. Even then, it might be too late in many areas.

There is a slightly bizarre side to all this interest and activity insofar as there is more than a good chance that the eclipse will be clouded out. But what might you possibly see for all this effort ?

The effect has been described as akin to deepest twilight rather than night. The overhead sky is dark, and the stars are out (the stars lower down being stars normally onlyn visible in winter), but sunset colors are in evidence all around the horizon.

Most intriguing will be the sight of the Sun's corona (the extended outer atmosphere ), normally invisible above the solar surface, but actually as bright as the full Moon, and stretching out to a couple of solar radii. The nature of the corona is baffling given that it is at a temperature of at least one million degrees, much higher than the 5800 degrees of the solar surface. To those of you with a bit of scientific knowledge, you will realise that this very high temperature cannot be caused by straightforward heat transfer because it contradicts the Second Law of Thermodynamics. Those without any such knowledge will still appreciate that, normally, the further you get from a source of heat the colder things become, not hotter. This high temperature of the corona was discovered in the 1940s and scientists still do not know the reason for it, unless the recent theories emanating from people working on the SOHO solar-research satellite prove to be correct. The eclipse will be especially useful for corona research - the high solar activity will give scientists a view of the most active corona they have seen since 1990 ( This time around, scientists have three solar satellites on hand to help them in their work ).

It is possible to view the chromosphere, the thin lower part of the atmosphere, which receives its name because of its pink or reddish color. The chromosphere has an uneven appearance due to the existence of arc-like prominences above the photosphere or surface of the Sun, individual prominences lasting anything from a day to several months. These prominences are different from the more short-lived flares which can last about a hour. Just like sunspots, both these phenomena are more common during periods of high solar activity and since the eclipse of 1999 will indeed occur close to a period of maximum activity in the Sun s 11-year cycle, there should be some good prominences to be seen even with the naked eye during 100% totality. Viewing will be greatly improved with binoculars or a telescope.

Immediately before the eclipse and just as it ends, the effect of sunlight shining thru mountains on the Moon's surface can cause the two related phenomena of Baily's beads (or diamond necklace) and the diamond-ring effect. Both have names which are maybe self-explanatory : first comes Baily's beads resulting from sunlight shining thru several lunar valleys. These "switch off" one by one, eventually leaving the Diamond Ring as the Sun shines brightly thru just one gap.

There is the apparently eerie atmosphere produced on Earth itself, as animals, including pets, start reacting as though it was night-time (or else acted confusedly). These apparently includes nocturnal species, like bats. And there is an unusual chill in the air.

I ought to state that the eclipse will start and finish about one and a half hours either side of totality. It is only when the Sun is about 80% covered, 15 minutes before totality, that things will start to become noticeably darker. Totality itself will be about 11.20 in the morning.

The last British eclipse on 29. June 1927 (at about 6.30 in the morning,) lasted only for 22-24 seconds and was indeed clouded out over most of its path across North Wales and Northern England. Obviously things still went dark but that was little compensation. Among the disappointed were many on the summit of Snowdon, the steam railway working from the early hours to transport many to the peak (an apparent advantage of viewing from an altitude is that you have a good view of the shadow advancing. Apparently from the ground, if you look West just prior to totality, you will still see an onrushing shadow ). More lucky were the estimated quarter of a million people on Southport beach who saw the eclipse in full (after engaging in night-long festivities), but as it headed towards North -East England, clouds tended to prevail again. One national newspaper reported : Sun completely eclipsed here - as usual .

I ought to modify my previous remarks because there was actually a total eclipse over the northermost part of the Shetlands ( fully total in the Faroes) in 1954, which I believe was about 70% total down in Southern England. Very few people mention this eclipse in the current literature, although there are obviously many British people who can remember it. In fact, my remarks about the 1927 eclipse being clouded out probably need to be modified to include the fact that many British people outside the zone of totality appear to have had decent enough weather to get a good view of an "almost total" eclipse.

Any report on the eclipse needs to include a warning about looking at the Sun directly. It has been known for schools to keep children indoors during an eclipse because of the perceived danger, but normal reflex action and/or basic intelligence SHOULD stop you looking at the Sun for too long with the naked eye. Nevertheless, I believe that any reflex action is not as "active" during the partial phases as it is normally, so people need to be warned - do not look at the Sun during the partial phases, and wait until the diamond ring effect vanishes before removing any eye protection, etc.

Basically, there is no point in looking directly at the Sun with the naked eye during its partial phase anyway, you are not going to see anything worthwhile. If you transgress this rule, you will feel a sensation analogous to the after-effect of looking at a light bulb for too long, except that the "after-image" will not go away. LOOK AT THE SUN FOR TOO LONG, AND YOU WILL BE LOOKING AT IT PERMANENTLY.

The Sun is so bright that even when 99.99% covered it can still cause eye damage.

However using a telescope or binoculars directly is a totally different situation and WILL cause immediate damage to your eye. The simple way to actually use a telescope or binoculars is to project the image of the Sun on to a screen. Since this will be a period of maximum solar activity, many sunspots should also be visible on the screen and you may be able to detect that they are not actually as dark as you might think when compared with the darkness of the moon s shadow - they will look more brownish (the fact that the sunspots are dark is an illusion due to contrast with the Sun s even brighter surface).

A more sophisticated way is to use specially-designed filters but the beginner should never use these without direct supervision and guidance. Not all filters are appropriate for viewing the Sun., they may reduce the light sufficiently but will not reduce the harmful infra-red radiation , the effects of which you will be unable to detect straight away.

None of this actually applies during the period of totality of course, it is perfectly safe to view the Sun after the Diamond Ring has vanished, but be aware of the Diamond Ring Effect at the end of totality, and divert your eyes before this occurs.

You could even project the Sun onto a screen using a pinhole of some description . The disadvantage is that the image will be fairly small and faint. In fact, the dappled effect produced in wooded areas is a projection of the Sun caused by twigs acting like some sort of a natural pinhole - this means that, during the partial eclipse period prior to and after totality, little images of the partially-hidden Sun will be projected on to the ground in the vicinity of trees (I believe you can re-create this effect using something like a cheese-grater). Another possible effect is shadow bands, similar to the wave-effect on the bottom of a swimming pool - look for these just after totality ends, when light from the Sun can still be considered to be coming from a point source.

A better method, possibly, than the last-mentioned is to use a mirror to project the Sun onto a card, or wall, or whatever. Experiment beforehand - if the mirror is too big, then a suggested method to try is to cut a small hole (maybe 2 cms. diameter) in an envelope, slipt the mirror in, and try that. But whatever you do, do not flash the mirror in people's eyes - please do not suggest this method to anyone who might be, in any way, immature in this manner.

Timetable (Cornwall)

January 1999 : There appear to be various stories cropping up which might be in the nature of urban myths - it is hard for me to check up. For example, there are claims of inadequate (or no) assistance from the central government for policing and extra facilities etc.. Claims of local councillors "burying their heads in the sand" are even harder for me to assess as to their veracity.

I have heard claims that the Tamar Bridge will be closed on the day, although that would not be an insuperable problem given that the total eclipse is visible from parts of Devon. However a good tip appears to be to station youself on the European mainland, listen to the weather forecast the day / evening beforehand, and then choose your location accordingly. Again, with no personal experience of the road / potential traffic situation in Europe, I can only put this idea forward as a suggestion which appears to offer a better bet than Cornwall / Devon. Intriguingly, the autobahn between Stuttgart and Munchen lies entirely within the zone of totality.

On top of everything else, there is also an air show at RAF St. Mawgam on the same day. This show claims to be the world's biggest military show, with usually 100,000 visitors per day.

Latest : The above airshow has been cancelled, officially because of the Air Force's commitment in the Balkans. However, there will be a short display off Newquay - the Red Arrows are scheduled to put in an appearance just after the Eclipse has taken place.

Astronomical Footnote : This period coincides with the annual Perseid meteor show which will peak on August 12. with the general peak of high activity predicted for the period 10 - 15 August.

The next total eclipse will be on 21. June 2001, visible from Angola/Zambia/Zimbabwe/Mozambique/Madagascar. There is however an annular eclipse potentially viewable from Northern Scotland on 31. May 2003. Weather permitting, this eclipse will be seen from places like Inverness, Thurso, Durness, Stornaway, the Orkneys and the Shetlands. At Durness, the eclipse will take place at 03:47, the Sun will just be over the horizon and will be 94% covered. The entire eclipse will be almost all over by the time the Sun rises over the rest of Britain.

References etc

August 11

It is 8:55 local time, Wednesday 11. August, and it is definitely Sunny here. Clouds in the distance, but don't look TOO threatening at the moment. Very, very hopeful situation for the eclipse.

9:55 Conditions have definitely taken a turn for the worse. Not just more cloud, but dark clouds appearing

10:30 Can see the Sun, and that the eclipse has started, but quite a bit of cloud around still

Well, despite over 90% cloud cover, the Sun showed itself quite often. As a first experience of an eclipse, it was quite disappointing - it was similar to twilight for a very short time, about 5 minutes straddling this, it was like the light levels on a winter's day. And the rest of the time it was little different from normal. It was obviously surprising how much light the Sun gave out despite being almost covered. No stars were out etc. - definitely need to go for 100% eclipse for the full experience.

Links to 1999 Eclipse