Observing eclipses
Matt Sarthy
eclipses? I have a No. 11 glass, but I think a No. 14 might be required.
Matt
Dave Storey
m_emirates.net.ae> writes
>Can someone tell me what number welder's glass is safe for viewing solar
>eclipses? I have a No. 11 glass, but I think a No. 14 might be required.
>
>Matt
>
IIRC you do need #14, which is not so easy to come by (lots of welders
never seem to use anything that dense). There was a thread about it on
sci.alt.astro a few months back, if you want to go search with
www.dejanews.com.
I would have thought mylar film was cheaper, easier to get, and more
likely to bounce if you dropped it, though!
Rgds
Dave Storey
Kevin/Monika
Not wishing to bet my eye's on it - or yours, but I would go for the 14,
check density with your supplier first.
On your own head be it
Kevin
Bob May
sun. The welding shop can tell you how much that gives you but I think
that it would be about right. I haven't tried it myself.
Have Fun and Keep Looking Up.
Bob May
Evan Zucker
> You can also use the lighter torch glasses under the #11 hood to see the
> sun. The welding shop can tell you how much that gives you but I think
> that it would be about right. I haven't tried it myself.
Are you talking about combining a #11 with a lower number, such as #3?
I can tell you from experience (7 central eclipses) that you definitely need
the equivalent of a No. 14. If your local welder store doesn't carry them
I'm sure they can order them.
Evan Zucker
San Diego, California
Evan Zucker
> I'm not sure where I read it but welder's glasses aren't a good idea. Even
> though they seam to block out enough visible light, I don't think they
block
> out enough of some of the other wave lengths that could also do damage to
> your eyes.
For what it's worth, I have been to 7 central eclipses and have used a No.
14 filter a number of times. If there was any damage to my eyesight, it
didn't keep me from passing the U.S. Air Force eye exams to become a fighter
pilot (which requires 20-20 uncorrected).
Brian P. Meany
I'm not sure where I read it but welder's glasses aren't a good idea. Even
though they seam to block out enough visible light, I don't think they block
out enough of some of the other wave lengths that could also do damage to
your eyes. Solar eclipse glasses are available and the cost (not much) is
cheap compared to risking your eye sight (priceless).
Hope this helps.
Regards and clear skies,
Brian P. Meany
Matt Sarthy wrote:
> Can someone tell me what number welder's glass is safe for viewing solar
> eclipses? I have a No. 11 glass, but I think a No. 14 might be required.
>
> Matt
Robert Wielinga
>> eclipses? I have a No. 11 glass, but I think a No. 14 might be required.
>I'm not sure where I read it but welder's glasses aren't a good idea. Even
>though they seam to block out enough visible light, I don't think they block
>out enough of some of the other wave lengths that could also do damage to
>your eyes. Solar eclipse glasses are available and the cost (not much) is
>cheap compared to risking your eye sight (priceless).
Welder's glasses are safe, but for visual observations a nr. 14 is
required. Read the following web-page about eye-safety during
eclipses:
http://sunearth.gsfc.nasa.gov/eclipse/safety2.html
Robert Wielinga
David Goldstein
>
> Can someone tell me what number welder's glass is safe for viewing solar
> eclipses? I have a No. 11 glass, but I think a No. 14 might be required.
>
This is a very interesting question. I am assuming that you are
referring to a total eclipse. I have commented before on seeing naked
eye sunspots without the aid of filters. I was also willing to bet that
a total eclipse can be viewed naked eye, during the minutes of
totality.
The reason that it is interesting is that I recently saw a special
about the total eclipse that was studied in Hawaii. I do not remember
the year, though. However, the astronomers made sure that their
equipment was functioning correctly then ran outside to view the eclipse
naked eye. One of the astronomers ran outside and looked directly at
the sun without the aid of any filters.
Now, you may not be willing to try this yourself; the experiences that
I have with viewing the sun with the naked eye--I have even taken
picture of setting suns without filters--tells me that it is possible to
do without filters. On August 11, I will be fortunate enough to view
the last total eclipse visible in Europe this millenium. I guarantee
you that I will be taking peeks at it without any filters :)
David
Chris Marriott
David Goldstein wrote in message <3749B520...@regio-info.de>...
> Now, you may not be willing to try this yourself; the experiences that
>I have with viewing the sun with the naked eye--I have even taken
>picture of setting suns without filters--tells me that it is possible to
>do without filters. On August 11, I will be fortunate enough to view
>the last total eclipse visible in Europe this millenium. I guarantee
>you that I will be taking peeks at it without any filters :)
When the Sun is totally eclipsed, it is perfectly safe to look at it
directly with the naked eye.
When even the smallest fraction of the Sun's disk is visible, however, you
*M*U*S*T* use a proper solar filter, or you risk seriously damaging your
eyes. Even looking at the setting Sun without suitable protection can damage
your vision.
Regards,
Chris
-----------------------------------------------------------------------
Chris Marriott, SkyMap Software, UK (ch...@skymap.com)
Visit our web site at http://www.skymap.com
Astronomy software written by astronomers, for astronomers
Kev
Did anyone else see the Cornwall Tourist Board chap on the breakfast BBC
news this morning ?
He was saying there's no problems with cars etc etc, and even if folk
couldn't get into the zone of totality, that it was still 99% and there was
no real difference !!!
Pity he didn't research the subject a little more.
Also, has anyone else been watching the eclipse railtour threads in
uk.railway about a week ago. Seems railtrack are thinking about terminating
some of the later booked specials at Paignton (fair enough) or Exeter (not
fair enough)
Kev
Letchworth & District Astronomy Society -
http://www.thetrainingpost.co.uk/ldas/home.htm
Kev's Home Page - http://websites.ntl.com/~kev.pye/
** From Kev Pye, remove nospam. to reply **
Martin Brown
Kev wrote:
> Did anyone else see the Cornwall Tourist Board chap on the breakfast BBC
> news this morning ?
They managed to catch and corner one then ?
They were giving someone a hard time on the R4 Today program over the bookings
in Cornwall being well down as a result of event mismanagement. Anyone who can
turn the last total eclipse of the century into a marketting disaster deserves
to be strung up.
> He was saying there's no problems with cars etc etc, and even if folk
> couldn't get into the zone of totality, that it was still 99% and there was
> no real difference !!!
> Pity he didn't research the subject a little more.
Luxembourg tourist board have recently woken up to the fact that totality is
going through the city and have started a slightly late marketting campaign to
fill all the hotels.
> Also, has anyone else been watching the eclipse railtour threads in
> uk.railway about a week ago. Seems railtrack are thinking about terminating
> some of the later booked specials at Paignton (fair enough) or Exeter (not
> fair enough)
Always supposing Railtrack can keep the west coast line working reliably for
the necessary journey down. Late arrival in Cornwall for the eclipse is not
going to be well received by the punters. Astronomers riot on late train will
make an unusual headline.
Regards,
Martin Brown
Mike Dworetsky
> >do without filters. On August 11, I will be fortunate enough to view
> >the last total eclipse visible in Europe this millenium. I guarantee
> >you that I will be taking peeks at it without any filters :)
>
> When the Sun is totally eclipsed, it is perfectly safe to look at it
> directly with the naked eye.
>
> When even the smallest fraction of the Sun's disk is visible, however, you
> *M*U*S*T* use a proper solar filter, or you risk seriously damaging your
> eyes. Even looking at the setting Sun without suitable protection can damage
> your vision.
>
Not only that, but if you attempt to look at anything other than the
final diamond ring, you will dazzle your vision so much that you will
not see the corona to full advantage for the next 30 seconds or so.
--
Mike Dworetsky
David Goldstein
> When even the smallest fraction of the Sun's disk is visible, however, you
> *M*U*S*T* use a proper solar filter, or you risk seriously damaging your
> eyes. Even looking at the setting Sun without suitable protection can damage
> your vision.
>
> Regards,
>
> Chris
You know, Chris, I cannot imagine that the women find you to be a very
romantic person ;-) I cannot count how many sunsets I have observed
over the Atlantic Ocean. They are really beautiful and I would not pass
them up for anything. Well, since I live in Germany now, I guess that
there are some things I would pass them up for.
David
David Goldstein
> You know, Chris, I cannot imagine that the women find you to be a very
> romantic person ;-) I cannot count how many sunsets I have observed
> over the Atlantic Ocean. They are really beautiful and I would not pass
> them up for anything. Well, since I live in Germany now, I guess that
> there are some things I would pass them up for.
>
>
> David
Please, change sunsets to sunrises :) I realized that I mistyped it
after I had sent this message. Of course, in Florida, I have seen the
sunsets over the Gulf of Mexico. I am still waiting for the opportunity
to drive to the west coast of France and catch the sunset there :)
Oops :)
David
Mick Simon
What color are your eyes, just out of curiosity? Darker eyes can usually
cope with bright light better lighter colored eyes.
Mick
Evan Zucker
> You know, Chris, I cannot imagine that the women find you to be a very
> romantic person ;-) I cannot count how many sunsets I have observed
> over the Atlantic Ocean. They are really beautiful and I would not pass
> them up for anything.
There's a big difference between observing a sunset with the naked eye,
which is relatively safe, and looking at the sun high in the sky.
I live in San Diego, which was fortunate to have the "ring of fire" sunset
annular eclipse on 4 Jan 92. It was fine to look at it without filters; in
fact, with filters you probably wouldn't see much because the atmosphere
acts as a natural filter and the sun is too dim to be seen through a No. 14
filter.
However, you definitely don't want to stare at sun unprotected before it's
near the horizon, and Chris is absolutely correct about the thin solar
crescent before totality dazzling your eye and killing the night vision that
you'll want during totality.
David Goldstein
>
> David,
>
> What color are your eyes, just out of curiosity? Darker eyes can usually
> cope with bright light better lighter colored eyes.
>
> Mick
Actually, my eyes are hazel. They are not particularly dark. I have
always lived under the principle that the body will tell you when it has
had enough. It is extremely difficult to look at the sun when it is
past the sunrise/sunset stage, due to it's brightness. Now, I understand
that the danger does not lie completely in the brightness, but in the
wavelengths of light that are reaching your eyes. Is it possible that
the sun's light is bent enough during sunset that the higher wavelengths
are no longer a problem?
David
Mick Simon
thickness of the atmosphere at low angles.
Mick
David Goldstein <sta...@regio-info.de> wrote in message
news:374C7B21...@regio-info.de...
Bill.
DG>. I am still waiting for the opportunity
DG> to drive to the west coast of France and catch the sunset there :)
Try the north of Scotland :o)
There was a wonderful sunset here last night, the incessant cloud does
come in useful sometimes ;)
Bill
PS. Another good one tonight, at around 10pm BST up here ;)
--
Email address has anti-spam, please remove *noreply* to reply ;-)
No Micro$oft applications used nor needed in posting this message :o)
Mick Simon
amount of atmosphere to reach us. At low angles, and especially at sunset,
the light must travel through much more atmosphere before it reaches us.
Just the atmosphere doing its job.
Mick
dondsnow <dond...@flash.net> wrote in message
news:374DF1C7...@flash.net...
> Hi, Mick -
> Since the sun has actually dropped below the horizon when we see it
> setting, do you think that much refraction of its rays filters out
dangerous
> wavelengths?
> Happy viewing,
> Don S
> Mick Simon wrote:
>
dondsnow
Since the sun has actually dropped below the horizon when we see it
setting, do you think that much refraction of its rays filters out dangerous
wavelengths?
Happy viewing,
Don S
Mick Simon wrote:
David Goldstein
>
> Hi, Mick -
> Since the sun has actually dropped below the horizon when we see it
> setting, do you think that much refraction of its rays filters out dangerous
> wavelengths?
> Happy viewing,
> Don S
The sun has definitely not dropped below the horizon when observing
sunsets :) Granted, it is not in exactly the same position as we see
it, but it is not far off, either.
By the way, I sort of misspoke what I meant to ask. I meant, does the
refraction lengthen the short wavelengths of light to the point where
they are no longer dangerous. The point was that elsewhere in this
thread, someone stated that observing the setting sun is also
dangerous. I do not agree with this, at all :)
David
Martin Brown
David Goldstein wrote:
> dondsnow wrote:
> > Since the sun has actually dropped below the horizon when we see it
> > setting, do you think that much refraction of its rays filters out dangerous
> > wavelengths?
> The sun has definitely not dropped below the horizon when observing
> sunsets :) Granted, it is not in exactly the same position as we see
> it, but it is not far off, either.
About half a degree down. 34' by convention. Coincidentally about 1 solar
diameter.
> By the way, I sort of misspoke what I meant to ask. I meant, does the
> refraction lengthen the short wavelengths of light to the point where they are
> no longer dangerous. The point was that elsewhere in this thread, someone
> stated that observing the setting sun is also dangerous. I do not agree with
> this, at all :)
Refraction has no important effect apart from introducing some chromatic
aberration which may allow you to see the green flash. Scattering in a mucky
atmosphere can remove a fair amount of the blue and UV components from the suns
rays, but has very little effect on the red and infra-red so you *can* still cook
your eye. In a very mucky atmosphere all wavelengths may be attenuated enough to
make it comfortable but not necessarily safe to look at. There are no pain
receptors in the retina so be very careful!
The longer the path length in the atmosphere the more light is lost, but relying
on this to protect your eyes from damage is very unwise. I guess most people have
watched nice red sunsets at some time or other and lived to tell the tale, but it
can still be dangerous.
Having spent a fair amount of time watching and trying to photograph green flashes
in conditions where the sky is very clear right to the horizon I find it most
unpleasant to look at the sun even when it is low down in clear conditions. I
follow the suns progress by watching its reflection in a window until only a small
fraction of the disk remains.
A few people manage to blind themselves at every solar eclipse by staring at it
without eye protection (or with unsuitable filters). I believe the blindness is
temporary, but that it does lasting damage. Any medics care to comment ?
Regards,
Martin Brown
Chris Marriott
David Goldstein wrote in message <374E5BAD...@regio-info.de>...
>The point was that elsewhere in this
>thread, someone stated that observing the setting sun is also
>dangerous. I do not agree with this, at all :)
That was me. Looking at the setting Sun with the naked eye is probably safe
enough. Looking at the setting sun through binoculars or a telescope is very
definitely NOT safe!
dondsnow
If viewing sunsets with unprotected eyes were dangerous, I would have either
started wearing glasses long before age 40 or have gone blind. Consequently, I
agree with you.
Happy viewing,
Don S
Mike Dworetsky
attenuated a great deal, some of the infrared radiation from the Sun is
not attenuated nearly as much and can cause eye damage which you will
not notice because (as has been pointed out by someone else) there are
no pain receptors in the retina.
Eclipse shades that meet CE kitemark standards cut out enough IR that
they are safe for this purpose.
It is probably safe enough to look at a setting sun for a second or so,
but do not stare at it. By the time it is down to the last flicker (if
you are watching for the Green Flash, say) then it is safe enough to
look at it, since you will see only a tiny part of the total Sun.
--
Mike Dworetsky
Martin Brown wrote:
>
> David Goldstein wrote:
>
> > dondsnow wrote:
> > > Since the sun has actually dropped below the horizon when we see it
> > > setting, do you think that much refraction of its rays filters out dangerous
> > > wavelengths?
>
> > The sun has definitely not dropped below the horizon when observing
> > sunsets :) Granted, it is not in exactly the same position as we see
> > it, but it is not far off, either.
>
> About half a degree down. 34' by convention. Coincidentally about 1 solar
> diameter.
>
> > By the way, I sort of misspoke what I meant to ask. I meant, does the
> > refraction lengthen the short wavelengths of light to the point where they are
> > no longer dangerous. The point was that elsewhere in this thread, someone
> > stated that observing the setting sun is also dangerous. I do not agree with
> > this, at all :)
>
Andrew T. Young
> >thread, someone stated that observing the setting sun is also
> >dangerous. I do not agree with this, at all :)
>
> enough. Looking at the setting sun through binoculars or a telescope is very
> definitely NOT safe!
A lot of categorical assertions have been made here by people speaking only
from personal opinion, not from having read the relevant literature. The
vision-science literature (not the literature of astronomy) is the place to
find the facts.
Retinal damage from looking at the Sun is not thermal but photochemical. The
dangerous blue and violet components of sunlight are almost completely removed
at sunset, and looking at the setting Sun, even with binoculars, is safe, as
long as it's within a solar diameter of the astronomical horizon (not the
apparent one).
Obviously, if you find the Sun too bright to look at comfortably, you shouldn't
look at it. But discomfort sets in well before damage, when the Sun is low in
the sky.
Now, about heating and infrared: First of all, the retina does not absorb
infrared appreciably -- which is why you can't see that part of the spectrum
well. Second of all, the heating effect is below the threshold of damage, even
when the Sun is high in the sky; but the safety factor is small. If you have a
normal pupillary reflex, the image of the Sun in the zenith heats the retina
only 4 degrees; the damage threshold for thermal damage is 10 degrees, so the
safety factor is only 2.5, under normal conditions. Almost all of the heating
occurs in a couple of tenths of a second, which means that if there is going to
be thermal damage, a quick look is as dangerous as prolonged staring.
The short time constant for heating is a direct result of the extreme thinness
of the retina.
Evidently, because of the short thermal time constant of the retina, we'd all
be blind from the many times we've all glanced at the Sun inadvertently, if
looking at the Sun could normally cause thermal damage. The eye has evolved to
be able to withstand these occasional accidental views of the Sun.
Now, about eclipses: When the Sun is almost totally eclipsed, the amount of
light entering the eye is reduced by a factor of 100 or more. This allows the
pupil to open up enough to exceed that safety factor of 2.5 mentioned in the
previous paragraph. Consedquently, this is the one situation where thermal
damage to the retina can occur -- but even then, only when the Sun is well
above the horizon. When the Sun is low, the wavelengths that are strongly
absorbed in the structures of the eye are removed by atmospheric scattering; so
a low Sun can be looked at safely (let's again emphasize that it must be *very*
low -- within a degrees or so of the astronomical horizon -- because of the
very rapid change in airmass at the horizon.)
This problem was discussed at some length by Dr. M. E. Mulder in his 1922 book
on the Green Flash. He was a retired professor of ophthalmology, so he was
aware that the danger to the eye is from short wavelengths, not from infrared.
He was exceedingly indignant at the foolishness of ignorant people telling
others not to look at sunsets to enjoy green flashes.
In short: the eye has evolved to be able to look at the full disk of the Sun
safely. You can look at the Sun on the horizon, even with binoculars -- indeed
that is the recommended technique for seeing green flashes, advocated by nearly
all experienced observers.
The eye is endangered in the partial phases of eclipses, when the ambient light
level is so reduced that the pupil opens up and the Sun is well above the
horizon. That is the situation in which "eclipse scotomas" occur. Marginal
damage may eventually be repaired over a period of months or even many years,
but severe eclipse "burns" (not really a burn, but thermal and/or photochemical
damage that kills cells in and behind the retina) can be very long-lasting.
A reasonable degree of caution should be exercised in viewing eclipses. Don't
look at the Sun when the exposed crescent is narrow, as your pupillary reflex
may not be activated enough to protect your eye. Eclipses are rare enough that
the eye has *not* evolved to cope with this rare situation.
--
Andrew T. Young
a...@mintaka.sdsu.edu
Keith Burnett
<mick...@worldnet.att.net> writes
>David,
>
>What color are your eyes, just out of curiosity? Darker eyes can usually
>cope with bright light better lighter colored eyes.
Brown, and I can look at Sunsets over the sea OK from Liverpool.
Probably so much gunk in the air that the brightness is dimmed.
Anything over one Sun diameter above horizon and I stop looking though.
Cheers
--
Keith Burnett
dondsnow
Thanks for your input. It reads as quite authoritative, to me. BTW, welcome
to nctu. Are you an amatuer or professional astronomer?
Happy viewing,
Don Snow
Orchid
I don't think I'm phrasing this right but, Can someone tell me how much of
the eclipse will we see from the north east of England? All supposing its a
clear day in the first place.... I think I am trying to say how dark will
it get :-)
Pat
Stephen Tonkin
>
>
>I don't think I'm phrasing this right but, Can someone tell me how much of
>the eclipse will we see from the north east of England?
85% (-ish) in Newcastle.
Noctis Gaudia Carpe,
Stephen
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Graham
Orchid wrote in message <7iv382$g5u$1...@news1.cableinet.co.uk>...
>
>
>I don't think I'm phrasing this right but, Can someone tell me how much
of
its a
>clear day in the first place.... I think I am trying to say how dark
will
>it get :-)
As dark as a dim winter's day at 09:00am.
Probably <g>.
But darker if it is already cloudy.
--
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WIMBORNE http://www.graham-wood.freeserve.co.uk/
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UK http://www.wessex-astro-society.freeserve.co.uk/
Harald R
Orchid skrev i meldingen <7iv382$g5u$1...@news1.cableinet.co.uk>...
>
>
>I don't think I'm phrasing this right but, Can someone tell me how much of
>the eclipse will we see from the north east of England? All supposing its
a
>clear day in the first place.... I think I am trying to say how dark will
>it get :-)
>
>
>
The darkness is only inside the path of the totality.
Harald
Visit www.astro-design.com
Orchid
Thanks for the information everyone
--
Pat.
Visit my web site
http://wkweb5.cableinet.co.uk/wyngarth.bears
Harald R
Harald R skrev i meldingen ...
Harald R
A Name
<a...@mintaka.sdsu.edu> wrote:
>Chris Marriott wrote:
>>
>> David Goldstein wrote in message <374E5BAD...@regio-info.de>...
>> >The point was that elsewhere in this
>> >thread, someone stated that observing the setting sun is also
>> >dangerous. I do not agree with this, at all :)
>>
>> That was me. Looking at the setting Sun with the naked eye is probably safe
>> enough. Looking at the setting sun through binoculars or a telescope is very
>> definitely NOT safe!
>
>A lot of categorical assertions have been made here by people speaking only
>from personal opinion, not from having read the relevant literature. The
>vision-science literature (not the literature of astronomy) is the place to
>find the facts.
>
Oh, I see. So because it is in print it's the truth right? Is
this the same resource where you read that oats lower cholesterol
but they failed to tell you the reason the test subjects got
lower ratings is because they ate so much oats they couldn't eat
any of the higher cholesterol foods? Or is this the resource
where they tell you that over-weight people have higher
blood-pressure, never mentioning the FACT that the mechanical
physics of the cuff of the sphygmomanometer is what causes the
discrepancy? Or perhaps this is the same bible of FACTS that has
told you that salt is no good for you, yet they found that people
on low-salt diets have 4x's the number of heart attacks over
those on high-salt diets? Yes, I see, because it's in print --
it's the "truth".
You people and your concepts of "facts" are so funny. No, what's
even funnier is the FACT that you people swallow what others who
claim to be "authorities" tell you -- hook, line, and sinker. Now
THAT is funny!
Rob O
Jeez, better stop all that reading, it can damage your eyes, if viewed
without adequate protection . . . .
R