MIRA 52
Winter 2000



Future solar eclipses 1996-2020

From the Editor

Welcome to a new MIRA and a new millennium, it will take me a while to get use to writing 2000 on dates and putting just 00 for the year (it does look a little strange).  I hope you enjoyed the new year and are experiencing clear winter skies to enjoy the stars and planets.
Last year for me was very memorable, I not only got to see the total eclipse in Austria (see MIRA 50), but also earlier in the year I had travelled with two colleagues to northern Sweden on a photographic shoot.  During the weekend there we motored up to the Artic Circle at 66·33°N.  This is further north than the whole of Iceland!  We had crossed into Norway at this point and drove up on the main highway arriving at the large Artic Circle visitor center; surrounded by vast rolling snow covered hills glistening in the May sunshine, it was really magical.  Around the center are markers showing the position of the Artic circle for different years.  This is slowly moving and alters its position, going north or south owning to wobbles in the Earth's rotation.  At the moment it is moving north as the Earth spins more upright at a little less than 23½°.  Over hundreds of years this can change by several degrees owing to the changing pull of the Sun and the Moon and movements in the Earths core.
For those of you who would like to see another total solar eclipse (count me in), or those folk who were clouded out last August, above is a map showing where to go for your holidays during the next 20 years!  This map is off the internet and shows the location of just the total solar eclipses world wide.  Africa seems to be the best bet for most of the next few eclipses and is fairly easy to reach with no jetlag.  The next two eclipses cross over southern Africa and the June 21st 2001 one will last over 5 minutes, the December 4th 2002 one will start off the African coast and end in the outback of Australia at sunset.

Ivor Clarke
Editor



Astronomical Observations in Anglo-Saxon England

by Mike Frost 

Astronomy in England has a distinguished history.  Observational astronomers such as Flamsteed and Herschel, theorists like Newton and Halley, led the world in their respective fields.  But what of astronomy before the scientific renaissance of the sixteenth century?  Suddenly the history becomes much patchier; but not completely empty.

There is a substantial historical record of life in England in the centuries either side of the last millennium.  Astronomical observations form an important part of this record; both as notable events in their own right and as presages of political events.  Are the observations accurate? What gets recorded, and what gets missed out?  Answering these questions involves a rewarding mix of astronomical and historical research.

There are two comprehensive historical sources covering the centuries around the last millennium.  The Venerable Bede, a monk based in north-east England, wrote an ecclesiastical history of England, which was completed by his fellow monks, four years after Bede's death, in 735 AD.  And the Anglo-Saxon Chronicle, of which several original copies still exist, is a year-by-year record of life in medieval England by scholars in the monasteries of Winchester, Canterbury, Peterborough, Abingdon and Worcester.  There are of course any number of other documents still in existence, but Bede's history and the Chronicle have the advantage of covering the span of time with reasonable consistency and ostensible completeness.

The appendix shows all the astronomical references I managed to find on reading through the two histories (fortunately they aren't too long!).  You can see that the anglo-saxon chroniclers took particular notice of unexpected events involving the Sun and Moon, also the arrival of new visitors to the skies.  From our perspective, it is easier to interpret some observations than others.  Let's see what we can make of them.
The most frequent and probably the clearest references in the Chronicle are references to solar and lunar eclipses.  For example, the Anglo-Saxon Chronicle for 1140. "Afterwards in Lent, the Sun and light of the day was eclipsed about noon when men were eating, and candles had to be lit for them to eat by.  This happened on March 20th, and men marvelled greatly".

Can we check if there really was an eclipse on March 20th 1140?  The answer to this is rather intriguing.  We can predict the dates of total solar eclipses with extraordinary accuracy, because the underlying theory of gravity is simple and very well understood (we can even use Newton's laws of gravity without the need for the tiny correction for relativity).  Nowadays there are commercially available computer programs to do the calculations.  And, yes, there was a total eclipse on March 20th 1140.

However, although we know with great accuracy WHEN eclipses occurred, we aren't able to calculate WHERE they occurred with anything like as much precision.  This is because of the irregular rotational period of the Earth, due to it not being a solid body.  You might be surprised that the rotation of the Earth IS irregular. But perhaps you'll recall that every once in a while (typically once in eighteen months or so) an extra second is added to or removed from the day to keep clocks in synchronisation with the Earth, which has speeded up or slowed down because of settling within its core.

One second in eighteen months doesn't sound like a large error, but each tiny change has a cumulative effect over the centuries.  The upshot is that we know the time of an eclipse with great accuracy, we also know at exactly what latitude the shadow touched the Earth, but the longitude of the eclipse depends upon precisely how much the Earth slowed down or speeded up in the centuries between the date of the eclipse and the present.  Consequently, historical records such as the Anglo-Saxon Chronicle can be used to estimate how much the Earth's rotational period has changed over the centuries.  So the eclipse predictions verify the historical record, and the historical record then tunes the eclipse predictions — very satisfying!

Furthermore, we can also use eclipse predictions to help resolve inconsistencies in the historical record.  Take for example the total eclipse of 2nd August 1133.  "In this year", the Chronicle says, ”King Henry went over sea at Lammas, and the second day as he lay and slept on the ship the day darkened over all lands; and the Sun became as it were a three night old Moon, and the stars were about it at mid-day. Men were greatly wonder-stricken and were affrighted, and a great thing should come hereafter.  So it did, for the same year the king died on the following day after St Andrew's Mass-day, December 2nd in Normandy."  The interesting thing here is that the Chronicle is for the year 1135, when there was no eclipse.  What's going on?

There are a number of possible explanations. First, the eclipse calculations might be wrong; however, as we've seen, the eclipse barely seven years later is correctly calculated by our present day computer programs.  Besides, there are other chronicles which confirm that the eclipse occurred in 1133.  Second, it isn't always straightforward for us to work out what account belongs to what year, as there are inconsistencies between the various copies of the chronicles.  Third is the possibility that the chroniclers might have been mistaken over the date of the eclipse; the Chronicle was at this time written retrospectively many years after the event.  What is more intriguing is the fourth possibility  that the recorded date of the eclipse was adjusted to line up with subsequent political events.  Maybe, as far as the chroniclers were concerned, King Henry's death needed to be foretold, and if the eclipse happened too soon then the historical record needed to be adjusted.

The association of phenomena in the heavens with events on Earth is apparent elsewhere.  After the deaths of Aelfwald, king of Northumbria in 789, and Ralph, archbishop of Canterbury in 1122, lights are recorded in the night sky.  Ralph, in particular, gets a spectacular send-off, "a great and extensive fire near the ground in the north-east which continuously increased in width as it mounted to the sky.  And the heavens opened into four parts and fought as if determined to put it out."  Almost certainly this is an aurora borealis.  Most memorable of all is the ”hairy star" which made its way across the sky in April 1066, which we now know to be Halley's comet.  This of course was recorded visually in the Bayeux Tapestry, but the Chronicle is in no doubt of its importance.  It was a "portent such as men had never seen before" and the arrival of William the Conqueror three months later confirmed this diagnosis.  However, if no invasion had been forthcoming, I suspect that the 1066 comet would have joined the other eleven comets in the Chronicle, none of which were regarded as portents of anything!

The Chronicle is usually not so much manipulative as selective.  For example, total solar eclipses are very rare in any given location, but total lunar eclipses can be observed much more often, on average every five years or so.  Yet lunar eclipses are chronicled much less frequently than this.  Why?  In part it is because they are rather less spectacular  a clear view of a total solar eclipse is completely unforgettable, but an eclipse of the Moon is less impressive. However, the recording of lunar eclipses in the Chronicle is very uneven.  For example, there are four lunar eclipses recorded in the twelve years from 795 to 806, three between 1110 and 1121, but none at all for 175 years between 904 and 1078.  The recording of lunar eclipses seems to go in and out of fashion, probably as the writers of the Chronicle change.  Whoever was writing the Chronicle in the early twelfth century was keen to record lunar eclipses, but had little idea as to their cause.  Two of the three lunar eclipses are recorded as happening on the ”fourteenth day of the Moon".  The chronicler presumably didn't notice that the third eclipse recorded, just like every other lunar eclipse, also occurred at full Moon.

We can see that Anglo-Saxon chroniclers were quite capable of selecting the astronomical observations they wished to record; but did they ever go one step further and make up astronomical events to suit their political narrative?  To their credit, it is difficult to pin a forgery on them, although some of the transient sky phenomena are impossible to prove one way or another.  Is it really true that "the sign of the holy cross appeared in the Moon" one Wednesday in 806?  It's possible — there are certain phenomena associated with ice crystals which can produce cross-like effects — but of course we will never know for certain.  We can make a better assessment of eclipses, where we have our own calculations of what actually happened.

I compared the list of solar eclipses recorded in the Anglo-Saxon Chronicle and Bede's ecclesiastical history, with the list of eclipses in Sheridan Williams's comprehensive ”UK solar eclipses from Year 1".  The two contemporary sources mention five of the eight total and annular solar eclipses over England in the period 664 to 1140.  The missing eclipses are in 758, 968 and 1023.  In the earlier parts of the Chronicle, however, there are references to solar eclipses, in 538, 540, 756 and 809, which are not listed by Mr Williams.  These may have been partial eclipses (which Mr Williams does not tabulate), but, as you may have realised from the partial phase of August's solar eclipse, partial solar eclipses need not be very noticeable. Perhaps the most interesting of the early eclipses is 756, where an appendix to Bede's history records an eclipse of the Moon two weeks after the eclipse of the Sun.  Because of the favourable geometry, a lunar eclipse is quite likely to happen at the full Moon immediately before or after a solar eclipse; indeed, the August 11th eclipse was preceded by a lunar eclipse at the end of July (although in this case it was only partial and not visible from the UK).  So I am inclined to give the benefit of the doubt to Bede's successor, and suggest that perhaps Mr Williams missed an eclipse! 

We might conclude that the Anglo-Saxon chroniclers were quite fastidious about recording extraordinary astronomical events, even if they were sometimes prepared to fudge the dates for political reasons.  But I would like to finish by pointing out that there was at least one event that the chroniclers should have recorded but didn't.  In view of their track record for observing everything else, the omission is, in my opinion, quite astonishing.  The missing record from the Chronicle is the supernova of 1054, which created what we now know to be the pulsar in the Crab Nebula, in Taurus.

Supernovae are very rare but very spectacular. In our own Milky Way galaxy, we only know of four for certain during the last millennium (there have probably been others hidden by the dust clouds in the galactic centre).  The only two supernovae recorded in Europe were in 1572 (observed by Tycho) and in 1604 (observed by Kepler).  The 1054 supernova is the only other one which could have been seen by the naked eye from Europe this millennium; the remaining candidate, the 1006 supernova in Lupus, was too far south in the sky for Europe.  Both the 1572 and 1604 supernovae were easily visible to the naked eye for weeks, reaching the same magnitude as the brightest stars in the night sky. With our knowledge of the distance from Earth to the supernova remnants, we expect the 1054 supernova to have appeared brighter still.

The primary source of observations for the supernova of 1054 is from Chinese astronomers, who claim that the supernova was visible during daylight for three weeks during July 1054.  Had the supernova occurred during the winter, it would have been visible in the night sky for months.  Moreover, in recent years, corroborative observations have come to light from Hopi Indian rock paintings in Chaco Canyon, New Mexico and elsewhere (the Hopi did not have written records).  So, if the Chinese and Hopi astronomers considered the event worth recording, why didn't the Anglo-Saxon chroniclers?

We can only guess, of course, but there are a few possible explanations.  The weather, for a start.  Cloudy weather over England has ruined many an eagerly anticipated astronomical event — not least the last two solar eclipses!  But it would have to be a particularly poor summer for the sky to be continuously cloudy for three whole weeks.

Could it be, instead, that the Anglo-Saxons weren't very capable astronomers?  Many people today would be completely oblivious to a new arrival in the sky — at least, not until it had featured on television.  However, I don't believe this explanation.  I am certain that a star visible by daylight would have been noticed (perhaps with superstitious trepidation) by a majority of the population.  Moreover the 1054 supernova was without question much brighter than Halley's comet, which was recorded only twelve years later.

I am more inclined to believe that the supernova WAS observed from Britain, but that its exclusion from the Anglo-Saxon Chronicle was a editorial decision by the chroniclers.  I think there are two pointers to this.  First, there is a noticeable gap in astronomical events recorded during the first half of the eleventh century  nothing at all from 995 to 1066, even though there was a solar eclipse in 1023.  This gap probably corresponds to the Danish invasion of Britain in 1016 and the subsequent chaos as bands of Danish pirates pillaged the country. Second, an impressive arrival in the sky would surely have been interpreted as an omen.  Did anything of sufficient political importance happen in the years following 1054?  To my eye there is no outstanding event in England occurring during the 1050's.  (I'm told, however, that 1054 was a year of great significance in the middle-east — see the acknowledgements).  It's difficult, of course, to guess from our perspective what the chroniclers considered to be the significant events at the time.  But I can't help thinking that if the 1054 supernova had occurred just twelve years later, it would have been recorded in the Anglo-Saxon Chronicle, and, no doubt, the Bayeux tapestry too, as a portent foretelling William's invasion.

So perhaps the 1054 supernova was common knowledge amongst the general population, but its recording for posterity was blocked by the anglo-saxon equivalent of the spin-doctors.  Or maybe they simply had a cloudy summer!  Either way, an intriguing prospect occurs to me.  Whatever the weather, whatever the chroniclers' attitude, I find it impossible to believe that nobody in England managed to observe the 1054 supernova.  So could there be an obscure account filed away in some library or archive, from someone who observed the daylight star of 1054?  Perhaps it was during a brief break in weeks of bad weather, perhaps it was viewed with superstitious terror.  But, if there was an observer somewhere who had the foresight to commit their observations to paper, I'd love to find their account!
 


This article arose from a conversation with Dr Julia Crick, lecturer in medieval history at Exeter University.  Julia's husband, Dr Andrew Gilbert, spoke to our society last October, and I visited Andrew and Julia in Devon last August, standing beneath the cloud cover with them in Totnes on eclipse day.  I'd like to thank Dr Crick for her assistance with (and comments on) this article. The wilder speculations, however, are all mine! 

Dr Crick also points out that 1054 was a very significant year in the middle-east; it marked the Great Schism, the rift between the eastern orthodox church and the church of Rome.  So chroniclers in that part of the world (with, probably, much clearer skies) would have had both an event of historic significance on Earth and an impressive celestial spectacle to attach to it.  Unfortunately, I am not aware of any references to the Taurus supernova in middle-east chronicles.  But it should be noted that Arabic astronomy was relatively advanced at this time.  Perhaps the archives of the Arab scholars would be a fruitful source for a historian of science.
 

Sources / Further Reading:

The Anglo-Saxon Chronicle             (trans/ed G.N.Garmonsway,   Everyman 1953)

Bede's Ecclesiastical History of Britain       (trans/ed J.A.Giles, Bell 1894)

UK Solar Eclipses from Year 1             (Sheridan Williams, Clock Tower 1997):




Appendix:

Astronomical Observations from Anglo-Saxon England:

Sources:

ASC       Anglo-Saxon Chronicle.       There are several versions of this, kept at several monasteries around England, and covering different periods of anglo-saxon history.
      Version A is from Winchester, later moving to Canterbury
      Versions B and C are from Abingdon
      Version D from Worcester
      Version E from Peterborough
      Version F from Canterbury            (I've indicated which versions contain which quotes. When slightly different accounts of the same event are given, I've indicated the quoted version in upper case (e.g. A, E indicates that essentially the same account is in sources A and E, whereas C, D says that I've quoted source D but source C mentions the same event with a slightly different description).

VB        Bede's Ecclesiastical History of Britain

SW        Sheridan Williams, Eclipses from Year 1


Solar Eclipses:

Sheridan Williams tabulates all total and annular eclipses crossing the British Isles — I've noted here all the eclipses which cross England.

538      16 Feb      ASC (A,E) & VB      "In this year the Sun was eclipsed on 16 February from early morning until nine in the morning"

540      20 Jun      ASC (A,E) & VB      "In this year the Sun was eclipsed on 20 June, and the stars appeared very nearly half an hour after nine in the morning"

594                    SW predicts eclipse at dawn on 23 Jan, total over Northumbria

639                    SW predicts eclipse at dawn on 3 Sep, total over Midlands

664                    ASC (A,E) & VB confirmed by SW (1 May)            "In this year there was an eclipse of the Sun"

733      14 Aug      ASC (A,E) & VB confirmed by SW (annular only)                   "In this year Aethelwald captured Somerton; and the Sun was eclipsed, almost all the orb of the Sun seemed to be covered with a black and horrid shield"

756      9 Jan       VB            "In the fifth year of King Eadbert, on the Ides of January, there happened an eclipse of the Sun"

758                      SW predicts eclipse on 12 Apr, total along south coast

809      16 Jul       ASC (F)            "In this year there was an eclipse of the Sun at the beginning of the fifth hour of the day, on 16 July, on Tuesday, the twentyninth day of the Moon"

878                     ASC (A,E) confirmed by SW (29 Oct)                  "The Sun was eclipsed for one hour of the day"

968                     SW predicts eclipse 22 Dec, total across Cornwall (recorded by continental chronicler)

1023                   SW predicts eclipse on 24 Jan, total across most of Wales & England

1135      2 Aug      ASC (E) confirmed by SW (but dated to 2 Aug 1133)                "At Lammas (1 Aug) of this year king Henry went oversea; and the following day while he lay asleep on board, the light of day was eclipsed over all lands, and the Sun looked like a Moon three days old, and there were stars around it at mid-day"

1140      20 Mar     ASC (E) confirmed by SW                  "Afterwards in Lent, the Sun and light of the day was eclipsed about noon when men were eating, and candles had to be lit for them to eat by. This happened on March 20th, and men marvelled greatly"


Lunar Eclipses:

734      31 Jan      ASC (A,e) & VB      "In this year the Moon was as if it was suffused with blood"

756      24 Jan       VB                     "On the 9th before the kalends of February, the Moon suffered an eclipse, being most horribly black"

795      28 Mar      ASC (F)            "In this year there was an eclipse of the Moon between cock-crow and dawn on 28 March"

800      16 Jan      ASC (E)            "In this year there was an eclipse of the Moon at the second hour of the eve of 16 January"

802      20 Dec      ASC (E)            "In this year there was an eclipse of the Moon at dawn on 20 December" 

806      1 Sep       ASC (E)            "In this year there was an eclipse of the Moon on 1st September"

827      25 Dec      ASC (E)            "In this year there was an eclipse of the Moon on christmas morning"

904                     ASC (C)             "In this year was the Moon eclipsed"

1078      30 Jan     ASC (D)           "In this year the Moon was eclipsed three days before Candlemas"

1110      5 May      ASC (E)            "On the fifth day of May, the Moon appeared in the evening shining brightly, and afterwards little by little its light waned, so that as soon as it was night it was so completely extinguished that neither light, nor circle, nor anything at all could be seen of it, and so it remained until almost daybreak when it appeared at the full and shining brightly. In this same day it was a fortnight old"

1117      11 Dec     ASC (E)            "and for a great part of the night of 11 December, the Moon appeared to turn all bloody and was afterwards eclipsed"

1121      5 Apr      ASC (E)            "The Moon was eclipsed on the eve of 5 April, when it was fourteen days old"


Comets:

678      August       ASC (A)            "In this year the star 'comet' appeared in August, and for three months every morning shone like sunshine”

729                      ASC (a,E) VB       "In this year two comets appeared"

892                      ASC (A)            "after Easter, during Rogationtide or earlier, appeared the star which in Latin is called cometa; likewise men say in English that a comet is a long-haired star, because long beams of light shine therefrom, sometimes on one side, sometimes on every side"

903                     ASC (C,D)          "In this year a comet appeared"

975      Autumn      ASC (D)         "In the autumn of that year appeared that star known as comet"

995                       ASC (e,F)          "In this year appeared the star called comet (that is the long haired)"

1066      24 Apr     ASC (a,C,D)        "At that time, throughout all England, a portent such as men had never seen before was seen in the heavens.  Some declared that the star was a comet, which some called the 'long-haired star': it first appeared on the eve of the festival if Letania maior, that is on 24 April, and shone every night for a week”

1097      4 Oct       ASC (E)            ”Then after Michaelmas, on 4 October, a strange star appeared, shining in the evening and setting early.  It was seen in the south-west and the trail of light that shone out from it towards the south-east appeared to be very long, and was visible like this for almost a whole week.  Many men said it was a comet."

1106      16 Feb     ASC (E)            ”In the first week of Lent, on the Friday, 16 February, a strange star appeared in the evening, and for a long time afterwards was seen shining for a while each evening.  The star made its appearance in the south-west, and seemed to be small and dark, but the line that shone from it was very bright, and appeared like an enormous beam of light shining north-east; and one evening it seemed as if the beam were flashing in the opposite direction towards the star.  Some said that they had seen other unknown stars about this time, but we cannot speak about these without reservation, because we did not ourselves see them”

1110      Jun        ASC (E)            ”a star appeared in the north-east, its rays shining before it to the south-west; it was observed like this for many nights; later on in the night, when it rose higher, it was seen moving away in a north-westerly direction”

1114      May        ASC (E)            ”In this year, towards the end of May, a strange star was seen, shining with a long trail of light for many nights”


Meteors:

744                      ASC (E)            ”In this year there were many shooting stars"

1095      3 Apr      ASC (E)            ”Then after Easter on the eve of St Ambrose, which is on 4 April, almost everywhere in the country and almost the whole night, stars in very large numbers were seen to fall from heaven, not by ones or twos, but in such quick succession that they could not be counted”


Aurorae (?):

774                    ASC (A,E)           ”And a red cross was seen in the sky after sunset"

789                    ASC (E,F)           ”In this year Aelfwald, King of Northumbria, was slain, and a light was frequently seen in the sky where he was slain”

926                    ASC (D)             ”In this year fiery rays of light appeared in the northern sky"

979                    ASC (C)             ”This same year a cloud red as blood was seen, frequently with the appearance of fire and it usually appeared about midnight; it took the form of rays of light of various colours, and at the first streak of dawn it vanished”

1098                 ASC (E)             ”Before Michaelmas the sky appeared almost the whole night as if it were on fire”

1117      16 Dec    ASC (E)             ”Also on the night of 16 December, the heaven was seen very red, as if there was a conflagration in the sky”

1122      7 Dec     ASC (E)             ”On 20 October, Ralph, archbishop of Canterbury, passed away. Thereafter there were a great many sailors on sea and on inland water who said that they had seen a great and extensive fire near the ground in the north-east which continuously increased in width as it mounted to the sky.  And the heavens opened into four parts and fought against it as if determined to put it out, and the fire stopped rising upwards.  They saw that fire at the first streak of dawn, and it lasted until full daylight; this happened on 7 December”

1131      11 Jan     ASC (E)             ”In this year after Christmas, on Sunday evening, just after bedtime, all the northern sky appeared like a blazing fire, so that all who saw it were more terrified than ever before; this happened on 11 January”


Haloes (?):

806      4 Jun         ASC (E)

806      30 Aug     ASC (E)             ”On 4 June, the sign of the holy cross appeared in the Moon one Wednesday at dawn; and again this year, on 30 August, a marvellous ring appeared around the Sun”

1104      June      ASC (E)             ”On the following Tuesday [after Whitsuntide, 5 June] at noon there appeared four intersecting halos around the Sun, white in colour, and looking as if they had been painted. All who saw it were astonished, for they did not remember seeing anything like it”


Miscellaneous:

1106                 ASC (E)             ”On the eve of Cena Domini, the Thursday before Easter, two Moons were seen in the sky before day, one to the east and the other to the west, and both at the full, and that same day the Moon was a fortnight old”








Desert Storm
The 1999 Leonid Meteor Shower
by Mike Frost 

This report by Mike Frost shows again how important it is to be in the right place at the right time for astronomical observations.  I was lucky to be in Austria during last August's total solar eclipse whilst Mike was totally clouded out in Devon.   This time however, the tables were turned and it was most of the UK which was cloudy while Mike enjoyed a rare spectacular event in excellent conditions which we may have to wait another 33 years to see . . . .     Ivor Clarke, Ed.

Every November 17th or thereabouts, the Earth encounters debris from the periodic comet Tempel-Tuttle.  Tiny grains of dust impact the Earth's atmosphere, causing a shower of meteors we refer to as the Leonids, after the location in the sky from which they appear to radiate. Tempel-Tuttle's orbital period is 33.3 years, and the meteor shower's strength shows a sharp peak with the same period.  This has led to some of the strongest recorded meteor showers in history - most notably the storms of 1833 and 1966, which had rates of upwards of 100 000 meteors per hour, albeit for very short periods.

In recent years, therefore, attention increasingly focused on November 17th, and the prospect of another storm.  In 1998, observers were caught by surprise by an intense shower of fireball meteors, some sixteen hours earlier than expected.  Astronomers David Asher, from the Armagh Planetarium, and Rob McNaught of the Anglo-Australian Observatory carried out an extensive analysis, modelling the filamentary structure of the cometary debris and tracking the streams of debris shed at each perihelion.  They predicted that, for 1999, the Earth would intersect debris shed at the 1899 perihelion of Tempel-Tuttle, at 0200 hrs Universal Time on the morning of November 18th, producing a Zenithal Hourly Rate (ZHR) of around 1500 - 5000 meteors per hour — not quite in the same league as the 1966 storm, but nonetheless a mouth-watering prospect for meteor observers.  In 1966 the storm was seen from western America, but a 0200 UT maximum meant that this time the storm would be best observed from Europe, Africa and the Middle-East.

I joined the expedition organised by Explorer Tours to Sharm-el-Sheikh, at the tip of the Sinai peninsula in Egypt (the choice of venues was also appealing to me as it gave a chance to scuba dive the Red Sea).  Sharm is a modern, brightly-lit resort, but we had an observing site laid on twenty-two kilometres to the north, in a Bedouin encampment hidden in the sandy foothills of the Sinai mountains.  There was some sky glow to the south from Sharm, and some wisps of cirrus cloud, otherwise the night sky was dark, clear and ideal for observing.

We made a preliminary visit to our observing site on Saturday 12th.  Dr John Mason gave the party a guided tour of the sky, and we witnessed an unexpected treat.  The Taurid meteor shower was also active during our trip, at much lower levels than was expected from the Leonids, but our tour of the skies was suddenly and gloriously interrupted by an Taurids fireball, which appeared to fly between Jupiter and Saturn, exploding brilliantly (brightness estimated at -5 or better) and leaving behind a train which persisted to the naked eye for minutes, twisting into improbable shapes as the winds at different altitudes sheared the ionisation trail.

Early indications were mixed.  Leonid rates over Tuesday night rose to 100 per hr, without a premature peak.  On Wednesday, we arrived at our observing site at 11pm, and for the first hour, no Leonids at all could be seen, although this was principally because the radiant for the shower, the interior of the sickle of Leo, was still below the horizon.  As the radiant rose, and the Moon began to set, Leonid meteors began to pop into view.  Upwards of 80 visitors, including seasoned meteor observers, amateur observers with an eye for spectacle, and divers who had heard about nothing else all week from me, gathered at the Bedouin encampment and settled down on mats, mattresses and borrowed sun-loungers, to await the outcome of a long evening's observing.

From half-past midnight, rates steadily began to pick up.  Pretty soon Leonid meteor rates overtook those for Taurids and sporadics. Painstaking observers maintained counts of meteors, observing the sky away from the direction of the radiant, which could then be converted to a Zenithal Hourly Rate to allow direct comparison with previous showers.  Other observers set up cameras to take exposures over minutes of favourite portions of the sky, such as the bowl of the Plough or Orion, in the hope of capturing meteors on film as they streaked through the field of view.  Others set up video cameras, others fell asleep!  This observer settled back to enjoy the spectacle directly.  The air was warm, perhaps fifteen degrees centigrade, although there was a cool layer close to the ground which discouraged snoozing.  Our Bedouin hosts came round with welcome glasses of hot, sweet mint tea.

The time seem to accelerate past as we approached four o'clock.  Leonid rates rose gradually  now we were counting meteors per minute, not per hour.  At 3am observer counts were around 5 per minute, by 3.15 10 per minute, by 3.30 fifteen.  Those still asleep, such as the chap next to me who was snoring loudly, were nudged awake.  I think that by 3.45am we all realised something special was about to happen.

The next half hour was a quite extraordinary experience.  Meteors began to appear faster than we could take them in; first of all in bursts of twos and threes, then fives, sixes, sevens; two or three in parallel.  The spoken counts of the dedicated observers took on an urgency, then an exhilaration; every so often I would hear cross checking to verify how closely five minute samples were matching  for how could anyone be sure they were catching all the shooting stars in view?  The photographers were ecstatic  at three am, a meteor through the field of view was a cause for celebration, by four am it was almost a routine occurence, and people were hailing extraordinary shots  meteors through Orion's sword, or a close encounter with Jupiter.  Nobody was lying down now.  Like many others I got to my feet and simply turned round, very slowly, savouring the sight all around me.  The sky was full of shooting stars, in all directions, all the way to the horizon.  There were no fireballs matching the Taurid we had seen, instead a continuum of brightness from about -2 down to the limiting magnitude of 6.  Certain directions were favoured, most noticeably Ursa Major and the bowl of the Plough in the north-east, but every constellation in the sky had meteoric interlopers.  In the vicinity of the radiant, tiny tracks could be seen of meteors headed almost directly towards us, and to the north the horizon was occasionally lit by brighter meteors which emanated down from the radiant and terminated below our horizon.

From its peak at 4am the display began to dwindle gradually.  Meteor rates had halved again by 4.15 and then continued to decline. Venus rose, looking painfully bright to night-adapted eyes, and its appearence heralded the gradual brightening of the sky prior to dawn.  But, even as sunset approached, we could still see occasional brighter meteors punching through the twilight sky.  As dawn broke we headed back to Sharm; exhausted, exhilarated, and ready for some sleep!

At the storm peak, at 4am (0200 hrs UT), individual fixed-observer counts reached 50+, giving a Zenithal Hourly Rate of around 3000  right in the middle of Asher and McNaught's estimates and right at the time they predicted. Rates such as this had not been seen since the previous Leonid storm in 1966.  However the peak of the storm was short lived, so a meteor rate measured in meteors per hour is misleading. Perhaps the fairest indicator of what all-sky observers such as myself were seeing was that, at the peak, perhaps 200 meteors per minute could be seen the sky above the Sinai.  Whatever the measure, it was a silent, eerie, stunning sight, and not one that anyone present in the desert that evening will forget in a hurry.






Guide to Planetary Nomenclature 

The members who attended the first meeting of the year will remember the lecture by Neil Haggatj on the naming of the various features on the solar system bodies and how they follow a set pattern of rules drawn up by the governing body of astronomy The International Astronomical Union.  This was set up in the early years of the twenty century to control the naming process after it was starting to get out of hand with more atlases and star maps appearing often with different names for the same features.  This problem had started before the invention of the telescope and after 1610 when Galileo started to use his new telescope on the Moon and planets it was realised that there was far more detail in the heavens than can be seen with the eye so all these new features needed naming.  When a new set of observations was made the observer could call them what ever he liked, after his patron or the King and Queens of his country or his friends.  This went on for some time with various naming systems for the different bodies.  For instance even 100 years ago Percival Lowell at Flagstaff Observatory, Arizona saw lots of canals on Mars and they all needed naming!  It was IAU which finally put a stop to it and made it self the sole arbiter of the process.  The IAU also fixed the constellation boundaries in 1930 to the shape they are today.  These corrections were incorporated into the fifth edition of Norton's Star Atlas published in 1933.
 

Moon
Craters, ridges, fissures        Scientists, scholars, artists; small craters, common first names
Maria and other plains          Latin terms for weather conditions
Mountains                           Terrestrial mountain ranges
Valleys                                Topographic features adjacent to mountains

Mercury
Craters                               Artists, musicians, painters, and authors
Plains                                 Names tor Mercury in various languages
Scarps                                Ships of scientific expeditions or discovery
Valleys                               Radio telescopes

Venus
Canyons                            Goddesses of hunt: Moon goddesses
Coronas                             Fertility goddesses
Craters                              Famous women
Ridges                               Sky goddesses
Flow terrain                        Other goddesses
Linear features                   Goddesses of war
Mountains                          Other goddesses
Paterae                              Famous women
Plains                                Mythological heroines
Regions                             Giantesses and titanesses
Scarps                               Goddesses of hearth and home
Tesserae                            Goddesses of fate or fortune
Uplands                             Goddesses of love

Mars
Large craters                      Scientists who studied Mars
Small craters                      Villages of the world
Large valleys                      Names for Mars and star in various languages
Small valleys                      Terrestrial rivers

Satellites of Mars
Deimos                             Authors of works about the satellites
Phobos                              Scientists who sought or studied Phobos

Satellites of Jupiter
Callisto
Large ringed features          Homes of the gods and heroes
Craters                              Heroes and heroines from northern myths
Crater chains                     Mythological places in high latitudes

Europa
Craters                              Celtic gods and heroes
Linear features                   Persons associated with the Europa myth
Bright areas                       Egyptian place-names
Dark areas and pointed        Places associated with the Europa myth linear features

Ganymede
Craters                               Gods and heroes of ancient peoples in the Fertile Crescent
Parallel ridges/channels        Places associated with myths of ancient peoples
Bright areas                        Places associated with Egyptian myths
Long, narrow depressions     Gods of ancient peoples
Regions                              Astronomers who discovered Jovian satellites

Io
Active volcanoes                  Gods and heroes representing tire, Sun, and thunder
Paterae                               Volcanic gods and goddesses, mythical black-smiths, fire / Sun / thunder gods and heroes
Mountains                          Mountains associated with the Io myth
Plains and regions               Places associated with the Io myth
Small domed hills                Persons associated with the Io myth

Satellites of Saturn
Epimetheus                       Persons from the Castor and Pollux myth
Janus                                Persons from the Castor and Pollux myth
Mimas                               Persons and places from Thomas Malory's Le Morte d'Arthur legends
Enceladus                          Persons and places from Richard Burton's Arabian Nights
Tethys                              Persons and places from Homer's Odyssey
Dione                               Persons and places from Virgil's Aeneid
Rhea                                Persons and places from creation myths
Hyperion                          Sun and Moon gods
Iapetus                            Persons and places from Dorothy Sayers's translation of Song of Roland

Satellites of Uranus
Puck                                 Mischievous spirits
Miranda                            Characters, places from Shakespeare's plays
Ariel                                 Good Spirits
Umbriel                            Evil Spirits
Titania                              Female Shakespearian characters and places
Oberon                             Shakespearian tragic heroes and places
Small Satellites                 Heroines from Shakespeare and Pope

Satellites of Neptune
Proteus                            Water-related spirits, gods, and goddesses
Triton                              Aquatic names, excluding Roman and Greek
Nereid                              Individual Nereids
Small Satellites                 Gods and goddesses associated with Neptune / Poseidon mythology







The RGB Debate
(continued from last month)
By Clive Rogers

For night vision in humans, rhodopsin bleaching may be the crucial issue that makes the question something other than a simple "most sensitive colour (green) is best".  It is certainly possible that faint green is better than faint red, and informal experiments suggest it may be so.  But I wonder if anyone is aware of any carefully controlled scientific experiments that answer the question exactly how we astronomers are asking it.  I assure you my life is too valuable for me to use a green light at some star parties I've attended.

Red, being at the bottom of the visible end of the spectrum, naturally is not as capable of carrying as much detail as light of a shorter wavelength.  Blue light would seem the best at carrying information, but I understand that human eyes don't see objects illuminated in blue light very well.  Green light being somewhere in between is is very important for people with older eyes.  So even if you use reading glasses, you may need to increase the diopter power to read in red light.  When we look at fine detail on our charts we use cone receptors.  To achieve the same luminance with cone vision we require 4.9 times as much red light (640nm) as green light (530nm).  When we look at faint stars we use rod receptors.  To achieve the same luminance with rod vision we require 542 times as much red light as green light.  So, if we use an amount of red light on our charts which results in the same cone luminance as green light, the affect of this red light on our rods would be only 4.9/542 = 0.009 times as much as with green light.

Clearly red light would seem to win out but there are other issues that the above numbers don't address.  For instance: how well does the ink on a given chart absorb (or reflect) red vs. green light?  (This would affect contrast)  How well confined is the red and green light that is used?  Some filters pass an amazing amount of light outside their perceived colour.  Chromatic aberration of the eye between red and green light is about one diopter, so refractive error of the eye would differ depending on whether red or green light is used.  Finally, and maybe most important, does it really make any difference that red light bleaches rod receptors less than green light, if, with the low light levels we use, re-adaptation takes very little time anyway?  It's probably worthwhile to experiment with different colours.  If you use your maximum amount of accommodation, your near point for green light is closer to you than your near point for red light.  The near point for blue light would be even closer.  Usually, you would not use your full amplitude of accommodation to view print.  However, in dim light observers may view their charts as close as possible to help them see fine detail under poor conditions.  In that case green light might be preferred to red light.  If that is true I would expect an age difference with older observers having a greater preference for green light than younger observers do.

A quick pilot study with a battery box and 3 LEDs - I could select either a red, yellow or a green.  I used a printed page with 4 mm text, that I read at about 65cm distance.  After a not so extensive dark adaptation, I held the LED close enough to focus my progressive glasses for best focus at the wavelength, then I pulled away the LED to where the text was no longer readable.  The measurements were: green 130mm, yellow 130mm and red 180mm.  After this I used a piece of black flocking paper on the floor, with two square pieces of white paper, 8 and 16 mm (seen at about 1500 mm distance).  With the green LED raised as high as I could, about 2200mm, I could see the squares with some little difficulty.  With the yellow, I could see them about as well at 1800mm distance.  With the red LED, I needed to hold it 750mm above to see the targets well - they were about as easy to see with direct as with averted vision now.  So, the difference in magnitude between the illumination needed to see the test target and to read the text was Green 5*log (2200/130) = 6.1 magnitudes,  Yellow 5.7 magnitudes,  Red 3.1 magnitudes.

Like it or not, the way I did this experiment the red LED came out a clear winner.  Also, if I did the reading test with one eye closed, and then checked the square targets, there was in all cases a clear difference in dark adaptation between the eyes. There seems no doubt to me that if you want to be able to read fine print on star charts, you need enough light to affect your dark adaptation.

So my advice seems to be:  1)  If you use one eye for critical observing, use the other eye for chart reading and for the finder, etc.  2)  To read the fine print on star charts, use a magnifying glass  3)  Use red light, as faint as you can use.  Has anyone tried a different coloured light other than red to read a star map and what effects did it have on the night vision?  Is it true that the older you get the less you see in red light?  We know that coloured filters help to see the markings on the planets but what effects do they have on the eye?   Ever tried looking at the full moon through a telescope and then try and look around with the eye that was looking down the eyepiece at the moon?  Night blindness or what?  Or have you tried using different coloured filters to view the moon, what difference did it make?