Large partial solar eclipse March 20 (1 Viewer)

I hope I can post this okay here. It is a bit early, but I think it is better earlier than later.

There is a total or large partial solar eclipse 2015 March 20 at around 09 30 UTC for the maximum eclipse.
In London it is about 86% maximum and Aberdeen 94%. In the Faroe Isles it is a total eclipse as it is in Spitsbergen.

Birdwatchers will have binoculars, which can be used for projecting the Sun onto white card or a white piece of paper. I would use the cheapest binocular you have, perhaps a 10×25 or even an 8×21 cheap roof prism binocular.the Sun's heat can affect the internals of binoculars.

There will be eclipse glasses available, but I think that they will be quite insufficient for the numbers who try to view the Sun.

Unfortunately, if the weather is clear, I expect this to be a particularly difficult eclipse regarding eye damage. I expect that at least several hundreds will receive at least some permanent eye damage if the sky is clear. The partial eclipse is visible over large parts of Europe, where hundreds of millions of people reside. With modern communications, I expect that millions of people will try to view this. I'm always saddened to see crowds of people, even in places like Trafalgar Square, where many just look at the Sun without any protection whatsoever.

A good alternative, is to use a 5 mm mirror, or even a larger mirror taped over but with a 5 mm clear portion to project the sun's image into a room at a distance of say 5 m, onto a wall or ceiling.

My colleague says that even a 3 mm mirror gives good results at 5 m if the sun is in a transparent sky. The projected images about 5 cm across, with a 3 mm resolution or fuzzy bit with a 3 mm mirror and a 5 mm resolution or fuzzy bit with a 5 mm mirror. You may be able to see sunspots, although it depends how large they are, if they are present. Yesterday and the day before I saw a protected unaided eyes sunspot about 37 arc seconds penumbral size. Such a spot might be visible.

I hope that everyone on the bird forum will take care if they try to view this eclipse.

Let's hope for clear skies......

Binastro said:

Birdwatchers will have binoculars, which can be used for projecting the Sun onto white card or a white piece of paper. I would use the cheapest binocular you have, perhaps a 10×25 or even an 8×21 cheap roof prism binocular.the Sun's heat can affect the internals of binoculars.

Click to expand...

What you mean by projecting? Let the sun shine through the binocular (objective or ocular?), hold a paper behind the binocular and then watch the light spot on the paper?

Would a bigger and better binocular give better results than your suggested cheap compacts? Can a scope also be usefull?

Do you really think the sun in European March at 9:30 can do damage to a binocular?

Sorry, many dumb questions, but I'm just a birder, never seriously looked at stars and stuff up there...

. Dear Florian,
. Yes, you just hold the binocular as normal and have a piece of white paper or white card about 20 or 25 cm behind it.
You focus the binocular so at least one of the barrel's images is sharp. Or you can make both images sharp using the dioptre if necessary.
You must not look at the Sun at all with your unaided eyes.
If you have problems finding the Sun, use the shadow of the binocular on the piece of white paper until it is a minimum size, then you will get the image on the white piece of paper.

The smaller the binocular the better, a 50 mm aperture binocular has tremendous heat and can easily damage the eyepieces and also any plastic pieces inside the binocular. I find that a 10×25 is ideal.
Never use any optical instrument for viewing the Sun directly, even the smallest aperture would probably cause permanent eye damage, in less than one second. There are special filters etc. But you must be very experienced and take great care when using these.
9:30 AM or maybe 10:30 AM where you are, the Sun is devastatingly bright if you don't know what you're doing.
All wavelengths from ultraviolet, near blue, visible and infrared are dangerous to humans or for that matter animal eyes. I think that only humans are stupid enough to want to look at the Sun, but that's how we are with our higher intelligence.
Of particular concern, is when people are drunk, as the normal protective devices that we have don't work, and people just stare at the Sun idly, allowing the sun's image on our retina to leave a permanent track of damage. Luckily it's not summer, where people are lying on the beach maybe having had a few drinks.
Also, if one has taken antibiotics and other medication or drugs, damage occurs more quickly.
Anyone who has had eye surgery should not even bother without consulting their doctor.

Yes you can use a telescope, but I would not use a normal good quality spotting scope. You can easily damage the internals.
Ideally, you should have an old, say 60 mm or 3 inch long focus refractor with Huygenian uncemented two element eyepieces. This gives a wonderful image on the opposite wall, especially if you have the curtains drawn around the telescope. The image size can be say 20 cm across and show great detail on the Sun if there is anything visible. The image is sharp and wonderful. The best would be to have a camera obscura specially designed, but there are very few of these worldwide of high quality.

Looking at a map of where the partial eclipse will be seen, it covers vast swathes of Europe, Russia and Northern Africa and the Middle East. There may be more than 2 billion people living in these areas. The potential for large numbers of cases of permanent eye damage is large.

In the early 1900s, in Europe, solar eclipses permanently damaged the eyesight of thousands of people.
We are a bit wiser now, but not much.

Thanks for posting. I have a decades old welding visor glass that I use for such events (and for my work I have my eyesight tested twice annually), so far so good.

. Hi Samandag,
. If you use a welders glass it should be shade 13 where you can tilt it as necessary to get the correct density, or even safer, shade 14.
It is better to have the larger sizes so that there is no possibility of direct exposure to the sun.

It should have a a British standard marking or European marking.
This should be etched into the glass, or the ones I have, which are surface marked, I cover with sticky tape.
This also protects any sharp edges to the glass. I know that some people have bevelled the edges to make them smooth. If the filter does not have any markings you must assume that it is not safe.

If you use a complete mask of course you cannot really tilt it. In Britain the shade 14 is more difficult to get than the 13.

With any form of solar protection, either the dense welders glass or eclipse glasses, one should minimise the actual exposure time when observing the Sun. It is not a good idea even with these to have prolonged exposure to the sun.

And be aware of fake filters, which have been sold by unscrupulous or just unknowledgeable people.

The main thing is to get a reliable source.

Welders glasses are not really designed for solar observation, but I use them, although I only observe for, say, one minute a day.

One needs to have a very rigourous procedure when observing the Sun, to make sure that mistakes are not possible.

I remember watching a partial solar eclipse during school time back in the early 60's. The whole class went out to the school yard and we viewed the eclipse by holding a piece of glass that the teacher had blackened with a candle flame. :eek!: Those were the days!.......|=)|

Thank you, Binastro. My personal glass is large and British standard etched to grade 13 yet I use it only for fleeting glimpses of these beautiful and ethereal events.

I would urge all of the hundred or so people who have viewed or who are following this thread to follow all of the sound, practical advice given above ; it is not a rehearsal.

Think before you act with the Sun rising with exponentially increasing intensity.

This may be a useful opportunity for further observations with the Byfield Polarised binoculars and I may post some comments in due course.

Kind regards,

I am probably going to set up my refractor at my son's primary school.
Thought of just using the Herschel wedge (and filters) that I normally use for solar viewing and which is perfectly safe.
However I've now ordered a solar projection kit because (1) it's easier to get large groups to see something, and (2) it doesn't inspire these kids as much to look at the Sun through whatever optical instrument (binoculars, for example) they may have at home.

For just naked eye viewing without any instrument, would there be harm in using metallised mylar film? Not the astronomy grade but regular packaging grade? I think it has to be better than nothing - this eclipse will be at its height when schools have their morning break and I don't think it's realistic to expect the kids not to look at the Sun when they're outside.

. Hi Mark,
. Initially, I was going to say don't do it. I.e. don't use ordinary metallised mylar, as you have no idea what density it is or what the transmission curve is all the way from ultraviolet to infrared.

But having had a chat with a colleague he seems to think that it might be okay if the sun looks dim enough or use several layers if it isn't. But this is not completely realistic, as even two layers would be very dark if the film was any good at all.

If you use this material, and personally I am against using material that has not been rigourously tested in the laboratory for solar radiation, then you will have to check it for pinholes. And it is not long-lasting material.

Very importantly, you should tell the children to restrict the total viewing time, preferably to less than one or two minutes in total. Prolonged viewing through unknown dark material might be hazardous.

Another important test is to use the infrared controller on your television through the material.
With my television remote control I could not change the channels or turn it on or off through a safe filter until I got within about 20 cm. Without a filter I can change the TV channels up to about 6 m although I cannot get a good perpendicular line of sight to the TV.

You should try with a test sample of either a recommended visual solar filter, not a photographic solar filter, which is not safe for solar viewing, and see what distance you can change your television channels or other functions of the television.
You could also try eclipse glasses, and welders glass 13 or welders glass 14 if you can get it.
This will give you something to compare with the metallised mylar.
And the metallised mylar should all be from one roll of the same material. Any different rolls need to be tested separately.

. Further to the last post 10.
The hazards presented by solar filters can be great.
A gentleman, or should I say, individual, from Nottingham was selling through established astronomical Journal adverts his so-called solar filters for putting on the front of telescopes etc.
Because I have been viewing the Sun for decades and have researched the problem of eclipse blindness I made a special effort to try to see what these filters were.
I bought one, and it was not cheap maybe £30 or £40.
Luckily a colleague in one of the top universities did a full test of this, which would have been prohibitively expensive had I had to pay for it, and the spectrum showed that it was transmitting up to about 28% in the infrared, and was not safe with any wavelengths. Not only that but the optical quality was awful.
What he had done was to take pieces of plastic which gave a pleasant solar colour, and made circular pieces to fit in different size empty photographic filter holders that screwed into the front of lenses etc. And also a device for fitting it to telescope.
It took an enormous amount of effort to eventually get this man to stop selling these filters. We managed to get a fine barrister, who happened to be part of our association, and his letter to the seller of these dangerous filters was one of the most compelling letters that I've seen. Good barristers are really worth the money they usually get and probably more.

But after a few years this individual, under another alias started selling these filters again. He was convinced or convinced himself that his filters were safe. Unfortunately in this world there are Walter Mitty characters, who are out of touch with reality, or are just unscrupulous.

The sellers of snake oil, especially in the present time of the Internet, are numerous.

So if you do try to use these mylar films, please test them as rigourously as you can. And as I say instruct the children to restrict the total time that they view the Sun using it.

And make sure that nobody looks at the Sun directly with their unaided eyes. It takes between one and 20 seconds to cause permanent eye damage, which will probably last a lifetime. You only have two eyes which have to last your whole life. At the moment, there is nothing that the medical profession can do, once you have damaged your retina. And if you deliberately stare directly at the sun, your central vision will be damaged for the rest of your life.

As I've said before, some actors, including some of the best-known, were told to stare at the Sun to stop squinting when they were seen in movies. Their vision has been permanently damaged. People are basically stupid. And I include myself, as I have been observing the Sun most of my life. Luckily, I discipline myself from the age of 16 to take rigourous precautions to protect my eyes.
Unfortunately some astronomers did not, mainly through ignorance. I think that even Newton may have destroyed his eyesight with solar observation.

Some people think that I am too careful. But I see no reason at all why hundreds and perhaps thousands of people on March 20 should cause themselves permanent eye damage.

.Regarding the above posts 10 and 11,
. If you use the infrared TV remote control as a basic test of filters, you should install fresh batteries in the infrared remote control otherwise you can get false readings.

Binastro said:

. make sure that nobody looks at the Sun directly with their unaided eyes. It takes between one and 20 seconds to cause permanent eye damage, which will probably last a lifetime.

Click to expand...

Thanks for your extensive advice, Binastro.
I've sent an e-mail to the school offering my presence with a scope and suggesting they look at buying eclipse glasses.

The bit I quoted above is of particular concern to me.
Millions of kids in Europe are going to walk onto the schoolyard for their morning break just around the time of mid eclipse. I don't think it is realistic to tell them not to look at the eclipse at all. Keep them indoors then? What a shame...

I would think that in a secondary school one should get in touch with the senior science teacher.
Also the local and especially the national amateur astronomer Association in whichever country somebody is situated. They have probably got plans of how to publicise and advise on eclipse safety.

With primary schools, things are a bit different, as there is probably nobody of sufficient science ability to cope.
In such cases, unfortunately it might be best to keep young children indoors.

With secondary schools, I would think that projection using small mirrors into classrooms with appropriate facing windows would work with projection onto white screen or card. If the distance is more than 5 m it is likely that a 5 mm mirror will be better than a 3 mm mirror. There is still plenty of time for the science master to experiment.

And there is still probably sufficient time to buy projection devices specially designed for solar projection.

As to buying of eclipse glasses from approved astronomical suppliers, one can get a discount for a quantity, say 50 or 100 glasses. It would be well worth the money, even if one had to buy them privately and distribute them. Of course, one cannot take responsibility for the safety of any devices.

Even the makers of well-known specially designed solar filters have been extremely reluctant to give full details and specifications and guarantees of safety. They obviously are concerned with legal claims.

Wearing sunglasses, is counter-productive, as the pupils of your eyes increase in size and the dangers may be greater than without sunglasses.

Incidentally, soldiers, possibly in the Vietnam war, claimed to be unable to see with their shooting eye. When they were examined it was found that only one eye was damaged. It was clear that they had deliberately stared at the Sun using one eye. They were relieved of duty, so this ploy worked. I suppose it was preferable to have one good eye rather than risk being shot or blown up on duty.

How does the mirror diameter affect what's seen?
It would be relatively easy to put a telescope diagonal on top of a photo tripod, but do I then need to stop it down?

. Hi Mark,
. A star diagonal is better than a normal mirror as it is a front surface mirror, whereas normal mirrors are back surface mirrors. Also the quality of the star diagonal will be much better than a normal mirror.
You need to stop it down near to the actual mirror. I suggest, 3 mm 4 mm, and 5 mm holes either circular or square.this is for a 5 mm projection distance. You will have to see what the actual distance is in the classroom.
The larger the mirror, the lighter the image. However, the resolution is much worse with a large mirror, unless you are projecting over a very large distance. If the star diagonal is, say 25 mm across, I suppose you could project an image of the sun at 25 m, with the Sun's image 25cm across.

Once you have established how the mirror should be positioned, you could try to have two or more mirrors, but one mirror might give an image visible to a whole class of students, but maybe not a whole school.

I have not used mirror projection of the Sun for several years. It has been cloudy for the last few days, so I have not been able to experiment.

I think that the window should be facing perhaps South or Southeast. That is for Britain at 930 local time or Europe at 1030 local time. I have not checked when daylight saving time begins, so you have to take this into account. March 20 is about the equinox.

I think also that the mirror should be parallel to the wall on which you are projecting the sun's image. However, I'm not sure.
Better than a wall, would be a white screen, perhaps near the wall which you can rotate to any angle to give a circular image of the sun.
Depending, at which angle the sun strikes the mirror, I think that, say a 5 mm hole, may be a 5 mm circle or an oval or elliptical shape with a 2.5 mm semi-diameter along the long axis.
I have not been able to experiment, but if it is an apparent elliptical shape then the sun's image will be a bit dimmer.
So because there are so many variables, it would be important to try the mirror, either outside the classroom window, or just inside the classroom window with the window open or closed.
The brightness of the sun's image will also depend on how much darker the classroom is compared with the outside. And this also depends on how large the pupils of ones eyes are. Youngsters obviously will have larger pupils and can probably see a brighter image than much older people.

. Regarding the last post 17,
. You will probably need to unscrew the, presumably, 1.25 inch barrel in front of the star diagonal, so that the sun can reach the mirror, depending on the angle needed. I think that these barrels normally unscrew very simply.

I still have some 24.5 mm fit star diagonals, which are smaller, but most people will not have these. Usually these front surface star diagonals are over overcoated so maintain their reflectivity. But over time normal mirror surfaces tarnish and become less efficient.

. Regarding posts 17 and 18.
Because a 90° star diagonal mirror is recessed within the mirror housing, one needs to experiment on how to position it regarding the Sun and the projection screen.

I think that maybe the included angle between the Sun, the star diagonal and the projection screen should be 90°, so that the full area of the mirror can be utilised as necessary. And so that any masks reducing the aperture can work properly.

If the angle is not correct then it may severely obstruct the beam.

Thanks. Sounds like there's a lot of variables. Perhaps I'll just play with this over the next couple of days to try it out.