1999 eclipse
An eclipse for Britain
1 The path of the umbral
and penumbral shadows
during the total eclipse of
11 August 1999. The area
shaded in dark grey is the
path of totality whereas the
lighter shading indicates
those areas where a partial
eclipse will be visible. The
dark vertical bars running
across the path of totality
are spaced at 15 minute
intervals. The bar to the
south west of Ireland
represents the point of
maximum eclipse at
11.00 BST.
Next August sees the first total
solar eclipse on the British mainland since 1927 and the last until
2090. Steve Bell sets the scene.
O
n Wednesday 11 August 1999, there
will be a total eclipse of the Sun. “So
what!” you might think; they happen
somewhere on the surface of the Earth practically every year, so what makes this one so special? Perhaps it is because it is the last total
eclipse of the Sun in the current millennium?
No. What makes this one so special to people
in the United Kingdom is the path of totality.
The umbral shadow will pass over the Scilly
Isles, the southern half of Cornwall, western
Devon and Alderney in the Channel Islands
during its three hour sprint across the surface
of the Earth. Those people fortunate enough to
be close to the central line of the eclipse track
will see a little over two minutes of totality and
experience the full spectacle of a total eclipse of
the Sun. With more than 40 million people
within a six hour drive of the path of totality,
it will present a once-in-a-lifetime opportunity
for the majority of people in the United Kingdom to see such an awe-inspiring sight from
the British mainland.
Total eclipses of the Sun are rare events in the
United Kingdom. Since 1700, there have been
only four total eclipses of the Sun visible from
our shores. Perhaps the most famous and well
documented was that of 3 May 1715, observed
by the renowned astronomer Edmund Halley.
Just after nine o’clock in the morning, the
4.14
umbral shadow swept across a 300 km-wide
swathe of southern England stretching from
Cornwall in the south west to the Wash in the
east. The maximum duration of totality in
England was a little over four minutes.
Only nine years later, another total eclipse
brought darkness early to most of south-west
England and Wales on the evening of 22 May
1724 not long before sunset. Totality lasted
only two and three quarter minutes. The
British Isles then had to wait a little over two
centuries for its next total eclipse. On this
occasion, the path of totality passed over north
Wales and northern England on 29 June 1927.
The duration of this eclipse was just under 25
seconds and occurred shortly after sunrise. For
many it was spoilt by poor weather, although
some observers in an eclipse expedition from
the Royal Greenwich Observatory were fortunate enough to observe the event through
breaks in the cloud at Giggleswick School in
North Yorkshire. The most recent total eclipse
was that of 30 June 1954. However, the only
part of the United Kingdom to see it as a total
eclipse was the northernmost part of the Shetland Islands. Readers may remember the
resulting deep partial eclipse visible in the rest
of the United Kingdom.
Great potential
The 1999 eclipse has the potential of being
seen by the largest number of people in the history of eclipse watching. It will be seen as a
partial eclipse in the north-eastern part of
America, the whole of Europe, the northern
half of Africa and western Asia. The path of
totality begins at sunrise about 400 km south
of Halifax, Nova Scotia at 10.31 BST. The
shadow then speeds across the Atlantic Ocean
in a mere 40 minutes, reaching the Scilly Isles
at 11.10 BST. Across Cornwall and Devon the
umbral shadow will be moving at just over
3000 km/h. Consequently, it spends just under
4 minutes on the British mainland from its
arrival in Cornwall, north of St Just, to its
departure from Devon, south of Torquay. The
maximum duration of totality (2 minutes and
6 seconds) can be seen from locations such as
Penzance, Helston and Falmouth. After taking
a minute or so to cross the English Channel,
participants in NAM99 visiting Alderney will
experience 1 minute and 47 seconds of totality.
The umbral shadow makes the short hop to
the tip of the Cherbourg Peninsula of northern
France and then moves out over the English
Channel once more. Soon after crossing the
coast of France again near Le Havre at
11.19 BST, the southern edge of the eclipse
track passes about 30 km to the north of Paris.
The southern tip of Belgium and the southern
half of Luxembourg also lie within the path of
totality. The city of Luxembourg itself experiences 1 minute 26 seconds of totality at
11.29 BST. The umbral shadow then sweeps
across the German border near Saarbrucken
where totality lasts 2 minutes and 13 seconds.
Between 11.31 BST and 11.39 BST the industrial heartland of Germany plays host to the
umbral shadow. Karlsruhe and Munich both
see 2 minutes and 12 seconds of totality whereas Stuttgart gets a further 9 seconds as it lies
closer to the central line of totality.
After crossing the Austrian border near
Salzburg at 11.40 BST, the umbral shadow
takes a somewhat more leisurely 6 minutes to
cross Austria as it slows to around 2500 km/h.
The northern edge of the track misses the Austrian capital, passing 40 km to the south of
Vienna. Moving into Hungary, the path of
totality crosses over Lake Balaton at
11.50 BST and then passes about 30 km south
of Budapest. Szeged, in the south east of
Romania, lies close to the central line of totality and experiences 2 minutes and 25 seconds
of darkness. Taking in the north-eastern tip of
Serbia, the umbral shadow then moves into
Romania. Greatest eclipse takes place near
Rimnicu-Vilcea at 12.03 BST and Romania’s
capital, Bucharest, sees 2 minutes and 27 seconds of totality shortly afterwards at
12.07 BST. The umbral shadow then sweeps
over the north-eastern part of Bulgaria and
passes over the Black Sea north of Varna.
The next landfall for the umbral shadow is
August 1998 Vol 39
1999 eclipse
Turkey, north east of Zonguldak at 12.21 BST.
The track passes 140 km to the north east of
Ankara but takes in the cities of Sivas and
Diyarbakir, bringing them 2 minutes and 12
seconds and 1 minute and 27 seconds of totality respectively. After passing over the northeastern tip of Syria, the track of totality passes
over the north-eastern part of Iraq at
12.45 BST. After bringing 1 minute and 54 seconds of darkness to Irbil and 2 minutes to AsSulaymaniyah, the umbral shadow reaches
Iran at 12.52 BST. It crosses the city of Isfahan
at 13.03 BST generating 1 minute and 38 seconds of totality. As the umbral shadow picks
up speed again, the path of totality crosses the
border of Pakistan at 13.22 BST, skirting the
Arabian Sea and reaching Karachi at
13.26 BST to provide 1 minute and 16 seconds
of totality. Reaching the Indian border at
13.28 BST, the umbral shadow traverses the
whole of central India in just over 8 minutes.
The shadow then leaves the Earth’s surface at
sunset in the Bay of Bengal at 13.36 BST. In
three hours and seven minutes, the umbral
shadow has covered nearly 14 000 km taking
in about 0.2% of the surface of the Earth.
To illustrate the appearance of the eclipse
from a particular location or “local circumstances”, let us take two examples – one of a
location experiencing totality and one seeing
only a partial eclipse. It has already been noted
that Falmouth is on the path of totality so let
us use it as an example. First contact takes
place at 9.57.06 BST, when the obscuration of
the Sun by the Moon commences. The Sun will
be 36° above the horizon at an azimuth of 111°
or 21° south of east. Over the next hour and a
quarter, more and more of the Sun’s photosphere will be covered by the Moon. Second
contact, or the beginning of totality, takes place
at 11.11.15 BST. For 2 minutes and 6 seconds
the Sun’s disk will be obscured only to reappear at “third contact” at 11.13.21 BST. At
maximum eclipse at 11.12.18 BST, the Sun will
be 46° above the horizon at an azimuth of 130°
or 40° south of east. Over the next hour and a
quarter, the Sun’s disk gradually reappears
with the eclipse ending at “fourth contact” at
12.32.25 BST. The Sun is now 54° above the
horizon at an azimuth of 158° or 22° east of
south. Local circumstances for a number of
locations seeing a total eclipse in the United
Kingdom and Europe are given in table 1.
The city of Leeds lies well to the north of the
path of totality but still sees a substantial fraction of the Sun obscured during the course of
the eclipse. First contact begins at
10.04.36 BST when the Sun is 37° above the
horizon at an azimuth of 118° or 28° south of
east. Maximum eclipse occurs an hour and a
quarter later at 11.18.55 BST when 88.8% of
the Sun is obscured. The Sun is now at an altitude of 46° and an azimuth of 139° or 49°
August 1998 Vol 39
11.10 BST
11.20
11.30
11.40
11.50
12.00
12.10
50%
80%
60%
90%
70%
80%
90%
90%
80%
70%
60%
90%
50%
80%
11.00 BST 11.10
11.20
11.30
11.40
11.50
12.00
12.10
12.20
12.30
2 The circumstances of the eclipse for Europe. The near-vertical lines link sites having the same times
of maximum eclipse, whereas those running nearly horizontally link places experiencing the same
degree of obscuration at maximum eclipse. Times are given in British Summer Time in intervals of 10
minutes across the top and bottom of the diagram. The percentage obscuration of the Sun is given on
the right and left hand side of the diagram. The latitude and longitude lines and annotation are shown
in grey. The shaded area is the path of totality.
65%
70%
75%
80%
85%
90%
95%
100%
3 The circumstances of the eclipse for the UK mainland and the Irish Republic. The near-vertical lines
link sites having the same times of maximum eclipse, whereas those running nearly horizontally link
places experiencing the same degree of obscuration at maximum eclipse. Times of maximum eclipse
are given in British Summer Time at five minute intervals. The appearance of the Sun at maximum
eclipse is shown for the relevant obscuration on the right hand side of the diagram. The symbol for
100% obscuration simulates the appearance of the corona and streamers. The latitude and longitude
lines and annotation are shown in grey. The shaded area is the path of totality.
4.15
1999 eclipse
Table 1: Total eclipse local circumstances
First
contact
h.m.s
Second
contact
h.m.s
Duration of
totality
m.s
Third
contact
h.m.s
Fourth
contact
h.m.s
United Kingdom
Camborne
Falmouth
Helston
Hugh Town
Land’s End
Lizard
Penzance
Plymouth
St Anne, Alderney
St Just
Torquay
Truro
09.56.58
09.57.06
09.56.52
09.55.41
09.56.22
09.56.48
09.56.37
09.58.14
09.59.37
09.56.30
09.58.59
09.57.15
11.11.00
11.11.15
11.10.57
11.09.34
11.10.19
11.11.02
11.10.35
11.12.50
11.15.15
11.10.24
11.14.03
11.11.23
2.04
2.06
2.06
1.46
2.03
1.59
2.06
1.42
1.47
2.05
1.12
2.01
11.13.05
11.13.21
11.13.03
11.11.21
11.12.21
11.13.00
11.12.40
11.14.32
11.17.02
11.12.30
11.15.15
11.13.24
12.32.03
12.32.25
12.32.05
12.30.24
12.31.21
12.32.13
12.31.38
12.33.51
12.37.12
12.31.26
12.34.55
12.32.26
Europe
Bucharest
Karlsruhe
Le Havre
Luxembourg
Munich
Ploiesti
Rimnicu-Vilcea
Rouen
Saarbrucken
Strasbourg
Stuttgart
Szeged
10.41.22
10.12.10
10.02.00
10.09.28
10.16.18
10.41.01
10.37.51
10.03.03
10.10.20
10.11.00
10.13.06
10.30.01
12.05.43
11.31.34
11.18.43
11.28.16
11.37.07
12.05.28
12.01.54
11.20.07
11.29.13
11.30.52
11.32.50
11.53.17
2.27
2.12
1.38
1.26
2.12
1.32
2.27
1.42
2.13
1.32
2.21
2.25
12.08.09
11.33.46
11.20.21
11.29.41
11.39.20
12.07.01
12.04.20
11.21.49
11.31.26
11.32.24
11.35.12
11.55.42
13.28.41
12.55.19
12.41.11
12.51.10
13.01.23
13.27.47
13.25.13
12.42.49
12.52.49
12.54.37
12.56.51
13.17.19
Table 2: Partial eclipse local circumstances
First
contact
h.m.s
Maximum
eclipse
h.m.s
Percentage
obscured
%
Fourth
contact
h.m.s
United Kingdom
Aberystwyth
Belfast
Birmingham
Cardiff
Cork
Dover
Dublin
Edinburgh
Glasgow
Leeds
Lerwick
London
Manchester
Newcastle
Norwich
St Peter Port
Southampton
Stornoway
10.00.32
10.01.35
10.02.50
10.00.21
09.56.01
10.04.48
09.59.41
10.05.45
10.04.45
10.04.36
10.13.30
10.03.31
10.03.34
10.06.00
10.06.16
09.59.01
10.01.36
10.06.24
11.14.56
11.14.01
11.17.57
11.15.35
11.09.04
11.21.49
11.12.47
11.18.02
11.16.48
11.18.55
11.22.38
11.19.49
11.17.53
11.19.28
11.22.16
11.15.32
11.17.48
11.16.04
94.2
86.9
93.5
97.2
96.4
97.5
91.2
81.9
82.3
88.8
67.9
96.6
90.1
84.9
92.3
99.9
98.8
74.8
12.33.36
12.30.29
12.36.57
12.35.08
12.27.04
12.42.25
12.30.14
12.33.42
12.32.22
12.36.48
12.34.07
12.39.54
12.35.58
12.36.18
12.41.36
12.36.42
12.38.09
12.29.00
Europe
Ankara
Belgrade
Berlin
Berne
Bratislava
Brussels
Budapest
Paris
Prague
Sarajevo
Sofia
Vienna
10.58.10
10.30.51
10.21.10
10.09.45
10.25.00
10.08.06
10.28.10
10.04.06
10.21.23
10.27.19
10.36.55
10.23.45
12.24.55
11.56.20
11.39.51
11.31.14
11.47.49
11.26.15
11.51.39
11.22.47
11.42.22
11.53.13
12.03.47
11.46.25
96.9
97.8
89.4
95.6
98.8
97.5
99.2
99.2
95.3
93.6
94.4
99.1
13.44.59
13.19.51
12.59.13
12.55.18
13.10.08
12.47.22
13.13.58
12.45.11
13.03.43
13.17.45
13.27.19
13.08.52
4.16
south of east. To put this into perspective, an
obscuration of more than 85% should bring
about a noticeable drop in the ambient light
levels. As the eclipse is partial, there are no second or third contacts. Fourth contact occurs at
12.36.48 BST when the Sun is 51° above the
horizon at an azimuth of 167° or 13° east of
south. No matter where you are in the United
Kingdom, a good view of the south-eastern
quarter of the sky is necessary for an unobstructed view of this eclipse. Local circumstances for a number of locations seeing a partial eclipse are given in table 2.
To observe the partial phases of the eclipse
safely requires both preparation and the proper equipment. The only time it is safe to look at
the Sun is during totality. At any other time,
the ultraviolet and infrared radiation will damage your eyesight even though you may not feel
any discomfort. It is also important to remember that the transition from totality to the partial phase of the eclipse occurs very rapidly.
Projection of the image of the Sun using a pair
of binoculars or a small telescope onto a piece
of card is a safe method of observing the partial phases of the eclipse. Welding goggles rated
at 14 or aluminized mylar filters carrying evidence of certification under the provisions of
the Personal Protective Equipment (EC Directive) Regulations 1992 for the UK and Council
Directive 89/686/EEC for the European Union
can also be used for personal observations of
the partial phases of the eclipse. Sunglasses,
smoked glass, gelatin filters, and exposed and
developed film do not offer sufficient protection for your eyesight and should not be used.
What will you see during the eclipse?
At first contact, a small notch on the limb of
the Sun will announce the presence of the
Moon. There will be little evidence for a drop
in either light levels or temperature until about
half the Sun is obscured. As the Sun becomes a
crescent, you may notice crescent-shaped
images on the ground around you if you happen to be standing near trees or bushes. These
images are caused by gaps in the foliage acting
as pinhole cameras. In the 20 minutes or so
before totality, ambient light levels will start to
drop noticeably and the light itself appears to
take on an eerie quality. These changes will
have an effect on the flora and fauna around
you. Some flowers may close up, animals may
behave as they do at nightfall and birds may go
to roost. As the light diminishes further, the
landscape may take on a greyish metallic hue
and shadows will become sharper.
As the sky darkens just before totality, some
of the planets may become visible. Jupiter and
Saturn, at magnitudes –2.5 and +0.2 respectively, will be setting in the west and may be
difficult to identify. However, Mercury and
Venus should be visible quite easily at totality.
August 1998 Vol 39
1999 eclipse
Mercury is 18° west of the Sun with a magnitude of +0.6 whereas Venus is 15° east of the
Sun with a magnitude of –4.1. For many people, this will be their first view of Mercury, a
planet which never strays too far from the Sun
as seen in British skies. Similarly, some bright
stars will also become visible. At the time of
the eclipse, the Sun is in the constellation of
Cancer, the Crab, a constellation devoid of
bright stars. However, bright stars which are
relatively close to the eclipsed Sun include Sirius, Regulus, Castor, Pollux and Procyon.
Events become more hectic in the last minute
or so before totality. An elusive phenomenon
known as “shadow bands” may be seen as low
contrast light and dark bands moving rapidly
across the ground. In the last few seconds
before totality, the Moon’s shadow can be seen
approaching rapidly from the west like a large
storm. Close to the horizon, you may notice
the oranges and yellows normally associated
with the twilight sky. This is the trailing edge
of the Moon’s shadow. Around the limb of the
Sun, the remaining photosphere breaks up into
discrete blobs of light. These are Baily’s Beads,
named in honour of Francis Baily who
described them in detail in 1836. This dramatic effect is caused by the final flashes of sunlight shining through gaps between mountain
ranges on the limb of the Moon. In a few seconds all the beads disappear except one. Nearly all of the bright photosphere is gone and the
Sun’s inner corona becomes visible as a pearly
white ring, sometimes irregular, around the
Sun. The final bright spot of the photosphere
and the ring formed by the inner corona gives
rise to the “diamond ring effect”. Within seconds this disappears and the corona comes into
full view. Totality has now begun.
During totality, the horizon in the direction
of the eclipsed Sun may appear orange or yellow, resembling the colours seen at twilight. In
the opposite direction, the sky may remain
moderately bright with clouds clearly visible.
The Sun’s corona can now be seen clearly,
extending radially away from the Sun in all
directions. It is pearly white in colour and may
extend several solar radii from the Sun depending on how active the Sun is at the time of the
eclipse. At the minimum of solar activity, the
Sun’s magnetic field binds the coronal gas into
streamers. These streamers are wide at their
base close to the Sun’s limb and curl up to a
point. At the poles of the Sun, the streamers
take on the appearance of thin streams of gas,
like iron filings following the magnetic field
surrounding a bar magnet. The more active the
Sun, the greater the number of streamers from
a wider range of latitudes. When the Sun is at
its most active, the corona may appear as a
broad ring-like feature. As the Sun is expected
to be close to maximum activity in 1999, we
can look forward to an active corona during
August 1998 Vol 39
4 A view of the whole sky as it will appear from Falmouth during totality. The centre of the plot
represents the point in the sky directly overhead, and altitudes above the horizon are marked in
intervals of 10°. Around the edge of the diagram is the horizon where the main compass points
are given with tick marks every 5° in azimuth. This diagram is applicable to all those parts of
the UK in the path of totality. All the planets likely to be visible to the naked eye during totality
and the main stars in the constellations of Ursa Major and Orion are plotted in addition to those
stars brighter than magnitude 2.0.
this particular eclipse. You may be able to see
the chromosphere of the Sun as a pinkish ring
around the edge of the Moon’s disk. Sometimes, when the Sun is particularly active, you
might be able to see signs of prominences,
pinkish arcs of gas within the inner regions of
the corona and the chromosphere.
Third contact
At third contact, the total phase of the eclipse
is over. What was seen in the moments before
totality now occurs in reverse time order. A
second “diamond ring” may appear, followed
by another display of Baily’s Beads. The
Moon’s shadow can be seen heading towards
the eastern horizon shortly after the end of
totality. The Sun’s photosphere appears to
brighten very rapidly after totality, and the
eclipse finishes when the Moon disappears at
fourth contact an hour and a quarter later.
Although the Channel Islands will see another total eclipse lasting a little over two and a
half minutes early on the morning of 3 September 2081, the eclipse of 11 August 1999 will be
the last opportunity to see a total eclipse of the
Sun from the British mainland for another 91
years. On 23 September 2090, the south-west-
ern tip of the Irish Republic, south-west England, most of the south coast and the Channel
Islands will again see a total eclipse lasting a little over two and a half minutes just before sunset. As the path of totality is more than 440 km
wide, totality will be seen by much of northern
France as well. Most of the UK will also witness
a partially-eclipsed Sun at sunset.
Totality can be every bit as addictive as
smoking and drinking, so I leave this thought
for you. The first total eclipse of the new millennium takes place on 21 June 2001. The
eclipse track covers passes over the South
Atlantic Ocean, Angola, Zambia, northern
Zimbabwe, Mozambique and southern Madagascar. Why do I mention this? Well, after
experiencing a mere 2 minutes or so of totality
you will definitely want to see more. This
southern hemisphere eclipse offers a potential
5 minutes of totality! ●
Dr S Bell, HM Nautical Almanac Office, Royal
Greenwich Observatory, Cambridge.
● Further information on the eclipse can be
found in The RGO Guide to the 1999 Total
Eclipse of the Sun available from Tor Mark
Press (tel. 01209 822101) for £6.99 inc. p&p.
4.17