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.
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
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
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
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):
Astronomical Observations from Anglo-Saxon England:
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
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"
ASC (A,E) & VB confirmed by SW (annular
only) "In this year Aethelwald captured Somerton; and the Sun was eclipsed,
all the orb of the Sun seemed to be covered with a black and horrid
756 9 Jan
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
predicts eclipse on 24 Jan, total across most of Wales & England
ASC (E) confirmed by SW (but dated to 2 Aug
1133) "At Lammas (1 Aug) of this year king Henry went oversea; and the
day while he lay asleep on board, the light of day was eclipsed over
lands, and the Sun looked like a Moon three days old, and there were
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"
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
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
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
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
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"
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
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”
”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”
”In this year, towards the end of May, a strange star was seen, shining
with a long trail of light for many nights”
744 ASC (E)
”In this year there were many shooting stars"
1095 3 Apr
”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”
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
1117 16 Dec ASC
”Also on the night of 16 December, the heaven was seen very red,
there was a conflagration in the sky”
1122 7 Dec ASC
”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
”In this year after Christmas, on Sunday evening, just after
the northern sky appeared like a blazing fire, so that all who saw it
more terrified than ever before; this happened on 11 January”
806 4 Jun ASC (E)
806 30 Aug ASC
”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”
”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”
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”
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,
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
Craters, ridges, fissures Scientists,
scholars, artists; small craters, common first names
Maria and other plains Latin terms for weather conditions
Terrestrial mountain ranges
Topographic features adjacent to mountains
Artists, musicians, painters, and authors
Names tor Mercury in various languages
Scarps Ships of scientific expeditions or discovery
Goddesses of hunt: Moon goddesses
Coronas Fertility goddesses
terrain Other goddesses
Goddesses of war
Giantesses and titanesses
Scarps Goddesses of hearth and home
Tesserae Goddesses of fate or fortune
Uplands Goddesses of love
craters Scientists who studied Mars
craters Villages of the world
valleys Names for Mars and star in various languages
Satellites of Mars
Deimos Authors of works about the satellites
Scientists who sought or studied Phobos
Satellites of Jupiter
Large ringed features
Homes of the gods and heroes
Heroes and heroines from northern myths
Mythological places in high latitudes
Celtic gods and heroes
Persons associated with the Europa myth
Dark areas and pointed Places associated with
the Europa myth linear features
Craters Gods and heroes of ancient peoples in the Fertile Crescent
Parallel ridges/channels Places
associated with myths of ancient peoples
Places associated with Egyptian myths
Long, narrow depressions Gods of ancient peoples
Astronomers who discovered Jovian satellites
Active volcanoes Gods and heroes representing tire, Sun, and thunder
Paterae Volcanic gods and goddesses, mythical black-smiths, fire / Sun /
gods and heroes
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
Persons from the Castor and Pollux myth
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
Persons and places from Virgil's Aeneid
Persons and places from creation myths
Hyperion Sun and Moon gods
Persons and places from Dorothy Sayers's translation of Song of Roland
Satellites of Uranus
Characters, places from Shakespeare's plays
Female Shakespearian characters and places
Oberon Shakespearian tragic heroes and places
Heroines from Shakespeare and Pope
Satellites of Neptune
Water-related spirits, gods, and goddesses
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
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
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?