Media coverage for this
eclipse, the last total one of this century, has already been so widespread
that a piece about it in early July in The Times (London) did not even feel it
necessary to mention the date.Media coverage for this
eclipse, the last total one of this century, has already been so widespread
that a piece about it in early July in The Times (London) did not even feel it
necessary to mention the date.
Long gone are the times when an eclipse was a sign of anger of the gods, or some other terrible portent of doom. However, some might argue that the cunning arrangement whereby the moon is placed in just the right orbit and is just the right size to cover the solar disc, which allows solar astronomers to study their subject perfectly is a good argument for the existence of a scientific sort of deity (!)
However, just to be on the safe side – the total solar eclipse will be on August 11. The shadow of the moon starts to fall on the Earth in mid-Atlantic, at 10.31 BST (all times in BST), 186 miles south of Nova Scotia. It will cross the Atlantic at 1,500 miles an hour and will be tracked by Concorde.
First landfall will be at 11.10 for totality will be on the Isles of Scilly. Then the shadow crosses to the UK mainland for 11.11, and all the area south of a line between Port Isaac and Teignmouth will be in darkness for 2 minutes and 6 seconds.
Totality will leave the UK via Alderney, one of the Channel Islands by 11.16, cross the Channel to France, and track across France from Cherbourg, cutting south of Paris (which will not see totality) to fall on Germany from Stuttgart at 11.34.
From there it will traverse to Lake Balaton, Hungary by 11.50, Rimicu Vilcea, Romania at 12.03, Turhal, Turkey at 12.26 and Isfahan, Iran at 1.04. The shadow will then fall over Pakistan and India but since it is the monsoon in both these countries it is not expected to be visible.
While Nasa is predicting only a 45% chance of seeing the eclipse in the UK because of the usual unpredictibility of the weather here, other scientists are more optimistic, since the eclipse itself creates a micro-climatic effect, with the cooling effect of the preceeding umbra often cutting down on cloud cover, rather like the effect at dusk. However, it is indeed more likely that there will be clear skies further on, for example in Romania (60% chance of clear skies) or Iraq (90%).
Solar eclipses only occur at new moon when the Moon passes between the Earth and Sun. At that time, the Moon's shadow crosses the Earth's surface and part of the Sun's disk will be covered or eclipsed by the Moon. There is a new moon every 29 1/2 days, but not a solar eclipse every month, because the Moon's orbit around Earth is tilted about 5 degrees to Earth's orbit around the Sun. As a result, the Moon's shadow usually misses Earth as it passes above or below our planet at new moon.
However, least twice a year, the geometry lines up so that some part of the Moon's shadow falls on Earth's surface and an eclipse of the Sun is seen from that region.
The Moon's shadow actually has two parts:
Penumbra - Faint outer shadow; partial eclipses are seen from within this shadow.
Umbra - Dark inner shadow; total eclipses are seen from within this shadow.
When only the Moon's penumbral shadow strikes Earth, we see a partial eclipse of the Sun from that region. Partial eclipses are dangerous to look at because the un-eclipsed part of the Sun is still very bright. (You must always use special filters or a homemade pinhole projector to watch a partial eclipse of the Sun safely)
If the Moon's dark umbral shadow sweeps across Earth's surface, then a total eclipse of the Sun will occur. The track of the Moon's shadow across Earth's surface is called the Path of Totality. It is typically 10,000 miles long but only a few miles wide. To see the Sun totally eclipsed by the Moon, you must be in the path of totality.
The Moon's orbit around Earth is not a perfect circle. It's actually a squashed circle or ellipse. As the Moon orbits Earth, it's distance varies from 221,000 to 252,000 miles. This 13% variation in the Moon's distance makes the Moon's apparent size in our sky also varies, again by 13%. When the Moon is nearest Earth, it appears larger than the Sun. If an eclipse occurs at that time, it will be a total eclipse. However, if an eclipse occurs while the Moon is on the far side of its orbit, the Moon appears smaller than the Sun and can't completely cover it. Looking down from space, we would see that the Moon's umbral shadow is not long enough to reach Earth. Instead, the antumbral or negative shadow reaches Earth. The track of the antumbra is called the path of annularity. If you are within this path, you will see an eclipse where a ring or annulus of bright sunlight surrounds the Moon at the maximum phase. Annular eclipses are also dangerous to look directly with the naked eye. You must use the same precautions needed for safely viewing a partial eclipse of the Sun
What to look for(Technical terms and stuff)
The eclipse can be quite advanced before it becomes noticeable that something is happening to the quality of the light. The fall in light level is very gradual at first but seems to accelerate particularly in the last ten minutes before totality. The greatest drop in light intensity is in the last four seconds and is very dramatic.
As the eclipse progresses the colour of the sky seems to change, and the intensity of brightly coloured objects seem to soften. If there are trees or bushes around, the little gaps between the leaves act as pin-hole cameras to throw many overlapping images of the crescent sun on the ground. This becomes more noticeable as the crescent sun narrows. (Try to remember to look around, and not just upwards towards the sun around this time, and also note how animal life is reacting – The Editor will be reassuring her bees, of course)
Baily’s Beads are a familiar feature of total eclipses. As the moon completely covers the sun, the razor-thin solar crescent breaks up into a chain of beads which gradually wink out. When the last one disappears, totality has started. It is now safe to observe with the naked eye, for the next two minutes or so, and only within the area where the eclipse is total. Outside totality protection should always be used (practice safe eclipse…!)
Just as the eclipse becomes
total, at the point where the last Baily’s Bead has disappeared, for a
second or two you may glimpse a bright red streak along the limb of the Moon.
This is an upper layer in the solar atmosphere called the
chromosphere.
The solar corona is the most noticeable feature during totality. The sun’s outer atmosphere of the sun is only visible to the naked eye during a total eclipse, and looks like pearly-white streamers.
Prominences are flamelike appendages to the corona, and may be visible, since the sun is active this year. As the moon moves across the face of the sun new prominences should become visible.
The combination of the moon’s total black, surrounded by the pearly-white of the corona with occasional flame red prominences, should be visually stunning. The sky will be a deep purple-blue and around the horizon the sky is usually an orange colour reminiscent of sunset. This strange mixture of colours can make everyday objects look positively surreal.
A glow around the horizon is due to sunlight outside the shadow of totality being reflected inwards. The actual colour can vary from reddish-orange to yellow.
During totality the sky is not as dark as night-time, so only the brightest stars may be seen; however, It is worth having just a quick glance around the sky to see which stars and planets are visible. There is always the possibility that totality will reveal a comet close to the sun which had not been observed before due to its proximity to the sun.
The chromosphere starts to emerge from behind the rim of the moon at the location where the photosphere will reappear at third contact. This occurs just a second or two before third contact and gives a good warning that the sun is about to reappear. You must start to protect your eyes again now)
The diamond ring is
one of the most dramatic features of the whole eclipse (as well as being
FTL’s logo!). As the first point of the photosphere reappears we see
something that resembles a giant diamond ring in the sky with the small portion
of the photosphere being the diamond and the rapidly fading corona being the rest of the ring. It is in fact the
same configuration as the last Baily’s bead at second contact but the
difference lies in the adaptation of our eye. At second contact our eyes are
used to the bright light and can perceive the last bead as a small point.
However our eyes become dark-adapted during totality and so the reappearance of
the sun can be dazzling (again, just like FTL).
Boring-but-vital eye safety stuff.
The sun radiates visible light but its photosphere also emits intense infrared and ultra violet radiation. This is what causes sunburn and it WILL also cause PERMANENT damage to your eyes.
The only way to view the uneclipsed or partially eclipsed sun is through a special filter.
The only time ever when it is safe to look directly at the sun is during totality when the moon completely masks the photosphere making it safe to look at the sun with the naked eye, through your telescope or with binoculars. BUT this only applied in the totality area, not outside totality.
While FTL is here providing a run-down of the safe ways of viewing the eclipse it is worth empasising that the safest way by far is to project the whole thing and watch via a pin-hole projection. Any viewing aids which are scratched or damaged in any way should not be used. They will not protect you.
Aluminised Mylar spectacles - Looking like '3D' movie theatre goggles, Mylar spectacles prevent harmful infrared and ultraviolet rays from passing into to the eye. They are made by coating a sheet of Mylar with a micron thin layer of aluminium to a quality assured standard. The sun is seen as a pale purple or blue disc.
If purchased within the European Union, they should conform to Directive 89/686/EC and carry the CE mark. If the surface of the protective Mylar is damaged in any way, the viewing spectacles should be discarded immediately.
Polymer spectacles - are made instead from a 'space-age' black polymer film. The sun is seen as a pale orange disc which looks more natural. Furthermore, being black on the viewing side, they suffer less from the behind-the-viewer reflections that can dog some metallised spectacles. Should also conform to Directive 89/686/EC and carry the CE mark.
Hold-up viewer - Made from either Mylar or polymer and mounted in a sheet of card, this type of viewer can be conveniently held up in front of the eyes. Especially suitable for people who wear glasses for distance viewing. Again, directive 89/686/EC and the CE mark.
Note also that using a telescope on the sun in daytime may damage it, since it is designed to be used in the cold of night.
Welding visor with number 14 filter - The green glass filter of a welder's face visor helps prevent arc eye by protecting the welder from harmful infrared and ultraviolet rays emitted by a welding arc. For this reason, a welding visor is suitable for observing the partial phases of an eclipse. Green glass filters are available in a range of numbers. The higher the number, the greater the protection. For eclipse observation, the lowest filtration which is safe is a 14/EW filter - EW stands for Electric Welding. In the United Kingdom, filters should be certified to BS679. Normal industrial BS679 Class 3 filters are suitable for eclipse viewing. Wearing a visor does cause perspiration, but its wrap around structure blocks peripheral vision which can dramatically increase the perceived effect of the eclipse. Note: most welding visors retail with an 8 E/W filter. This should NOT be used because it is not dense enough. Unfortunately, most DIY retailers cannot supply the higher 14 E/W density. A piece of Mylar or polymer filter can be used instead of the welding filter
Children and safety
Children's eyes are even more vulnerable to sunlight and its damaging effects; protection of their eyesight is paramount.
Children under the age of three should be left indoors or, at least in their prams and shaded from the sun. It is unlikely that children of this age will have any perception of the change to the sun or, any future memory of the eclipse. Be practical. They can watch the one in 2070
Children who are old enough to understand that something is happening to the sun should be encouraged to watch the eclipse, but safely. Try projecting the sun's image through a pinhole in a card onto their palms. This way they can catch the partial phase of the eclipse in their hands. Children can also be encouraged to find the places in the house and garden where the image of the partial eclipse is projected. As an added precaution – which will also enhance projection, do the projection through the curtains of a darkened room.
Never rely on sunglasses, damaged viewers or viewers which don’t have the CE safety mark, sunbed goggles, photographic negatives, photographic filters, floppy discs, compact discs, smoked glass, sweetie wrappers or crisp packets, a cloudy sky or even just squinting (this will cause blindness as well as wrinkles)
Finally, if you experience any disturbance in vision at any time up to 48 hours after observing the eclipse, even if you think you followed all the rules, seek medical help immediately. Don’t mess with your eyesight.
Two NASA researchers will be a 50-year-old mystery. David Noever and Ron Koczor of the Marshall Space Flight Center will be checking some hard-to-believe measurements reported 50 years ago by Nobel laureate Maurice Allais.
In 1959, at the enthusiastic urging of rocket pioneer Werner von Braun, a peculiar set of physics experiments first appeared in English as a four-part series in the journal Aero/Space Engineering. The author, Maurice Allais, was a skilled physicist with an interest in the behaviour of Foucault's Pendulum. From 1954 to 1960 he made careful observations of the motion of glass and metallic pendulums, hoping to discover some connection between gravity and magnetism. Despite years of careful work, he never succeeded in finding a link between those disparate forces, but he did observe something extraordinary. During the total eclipses of June 30, 1954, and October 22, 1959, he detected "anomalies in the movement of the ... pendulum" during the time when the Earth, the Moon, and the Sun were aligned.
"A remarkable disturbance has been observed at the time of the total solar eclipse--June 30, 1954. [which] cannot be considered as due to the disturbances of an aleatory order [chance]. "Neither can it be considered as produced by an indirect influence of known factors (temperature, pressure, magnetism, etc.). Finally, it cannot be identified with periodic lunisolar effects resulting from the actual theory of gravitation."
Maurice Allais, 1959, from the abstract of his articles in Aero/Space Engineering
When Allais won the Nobel Prize in 1988 he
revisited his experiments in his acceptance speech and again noted that the
phenomena he observed was "quite inexplicable within the framework of
currently accepted theories" of gravity.
Allais’ solar eclipse results are hard to understand, but he was
undoubtedly a meticulous scientist. His experiments were well conceived and he
repeated his measurements during two solar eclipses.
"If something strange is happening to Foucault
pendulums during solar eclipses, then it's a real mystery," says Noever.
"Is it some gravitational effect, a peculiar manifestation of tides, or
something else entirely? The idea that some unexplained aspect of gravity is at
work seems nonsensical when you consider that it would seem to imply planets
spinning out of their orbits over very long time scales (among other things).
Also, why would the effect show up only during a solar eclipse? The Sun, the
Moon, and the Earth are nearly aligned about once a month near the time of the
new moon. A solar eclipse takes place when they are precisely aligned.
If something is happening to gravity once a month, wouldn't we have noticed by
now?"
"The bottom line," said Noever, "is this: It's unlikely, but
Allais could have stumbled on to something important. So, rather than debate a
set of 50 year old measurements we're going to roll up our sleeves and try to
detect Allais’ signal directly."
"If Allais’ disturbance is real, and if it has something to do with
gravity, then we will be able to measure it to 10 significant digits,"
says Noever.
"The most likely result of our work on August 11 is that nothing
extraordinary will happen," says Noever, "but you never know. Von
Braun himself and certainly Allais would have smiled to see us revisiting this
mystery after 50 years."
As the famous physicist Max Planck once said, "For a theoretician really
worthy of the name, it may be said in passing that nothing could be more
interesting than a fact which runs counter to a theory .... For him [or her],
the real work begins at that point."
And Finally….Long gone are the times when an eclipse was a sign of anger of the gods, or some other terrible portent of doom. However, some might argue that the cunning arrangement whereby the moon is placed in just the right orbit and is just the right size to cover the solar disc, which allows solar astronomers to study their subject perfectly is a good argument for the existence of a scientific sort of deity (!)
Info: http://csep10.phys.utk.edu/astr161/lect/time/eclipses.html
http://sunearth.gsfc.nasa.gov/eclipse/eclipse.html
http://science.nasa.gov/newhome/headlines/ast17jun99_1.htm
For hints on photographing the eclipse http://sunearth.gsfc.nasa.gov/eclipse/SEphoto.html
Just to clear things up, since the papers have been full of even more contradictory, silly, patronising and downright unfathomably play-safe advice today in the UK - we have included the Royal Astronomical Society's statement on the matter verbatim on the features/eclipse page. Check with it.
ADVICE ON SAFE SOLAR VIEWING
A PERSONAL STATEMENT FROM B. RALPH CHOU, MSC, OD, A RESPECTED INTERNATIONAL
AUTHORITY ON EYE SAFETY
* * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *
A safety code drawn up by the Solar Eclipse 1999 UK Co-ordinating Group,
mentioned in Dr Chou's statement below and supported by the Royal Astronomical
Society, may be found on the following web site:
http://www.eclipse.org.uk/safety.htm
Contact details for Dr Chou, and a biographical note are at the end of his
statement.
* * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *
Statement regarding solar eclipse eye safety
Recently the Royal National Institute for the Blind (RNIB), UK Department of
Health, and organizations representing the eye care professions of optometry
and ophthalmology have issued advice advocating only the use of indirect
viewing methods to observe the solar eclipse of 11 August 1999. Several of
these organizations have actively discouraged the use of solar viewers that
enable observers to look directly at the sun during the eclipse. It is
disappointing to me that these organizations have chosen not to co-operate with
the Solar Eclipse 1999 UK Co-ordinating Group in presenting an unbiased, common
message on how to observe this spectacular natural event safely.
While the intention of these organizations is to ensure public safety during
the eclipse, they have ignored the scientific evidence that solar viewers are
safe when used as directed. Indeed, an examination of the scientific reports on
eclipse eye injuries published since the 1960s shows that the principal causes
of eclipse-related retinal burns are (in descending order): 1. Viewing the
partly eclipsed sun without protection; 2. Looking through the pinhole of an
indirect projection viewer (sunscope); 3. Viewing the sun through sunglasses,
photographic neutral density filters, or other inappropriate devices.
There has never been a substantiated or anecdotal report of eclipse-related
retinal injury arising from the use of a mylar solar viewer.
Messages that discourage an activity or behaviour, particularly when they are
intended for young people, can backfire. This is especially so when the
warnings turn out to be inaccurate or wrong. The advice issued by health
authorities around the world on the subject of eclipse watching is a case in
point. Unfortunately, many of these messages are designed to scare people from
seeing the eclipse at all. When people heed these warnings and later learn that
others saw the eclipse safely by disregarding that advice, they may feel
cheated out of the experience. How then will they react in future to other
health- related advice on drugs, alcohol, AIDS, and smoking from the same
authorities?
Despite their good intentions, these organizations are doing the public a
disservice by continuing to advocate this extremely conservative position on
watching the solar eclipse.
B. Ralph Chou, MSc, OD
Associate Professor
School of Optometry, University of Waterloo
Waterloo, Ontario, Canada N2L 3G1
Tel: 519-888-4567x3741 Fax: 519-725-0784
e-mail: bchou@sciborg.uwaterloo.ca
Biographical note
Dr. B. Ralph Chou is Associate Professor of Optometry at the School of
Optometry, University of Waterloo in Waterloo, Ontario, Canada. Dr. Chou's
research is in the area of industrial and environmental eye protection with
special interest in the analysis of, and protection from, optical radiation and
impact hazards. He currently serves as Vice Chairman of the Technical Committee
on Industrial Eye and Face Protection of the Canadian Standards Association,
and as a member of the Eclipse Information Committee of International
Astronomical Union Commission 46 (Teaching of Astronomy).
An amateur astronomer for 30 years, Dr. Chou has observed 12 total and 2
annular solar eclipses and led 8 eclipse expeditions. He has lectured on solar
eclipse eye safety in the Philippines, Canada, the U.S.A., Romania and the
Netherlands Antilles. He participated in eye safety campaigns for the total
solar eclipses in Canada and the U.S.A. (1972, 1979, 1984, 1994), Mexico
(1991), Papua New Guinea (1983), India and the South Pacific (1995) and the
Caribbean (1998).