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Large partial solar eclipse March 20 (1 Viewer)
- Thread starter Binastro
- Start date
. If anyone doubts the power of the sun, I have just read an online report from the Evening Standard.
' We've lost everything', say family after home destroyed by Nutella jar.
They have just been left with the shirts on their back after blaze sparked by sunbeams focused by a glass jar on a windowsill.
The damage is estimated at £250,000. Their pet Jack Russell terrier died.
The light was focused on part of the floor which had a dolls house which caught fire and flames spread to the roof.
The house looks basically just like a shell now.
This is not the first time I've heard of such an event.
One event was caused by a glass paperweight. And I've seen a magnifying make-up mirror concentrating the sun's rays producing great heat.
Also of course a magnifying glass and even spectacles can start a fire.
Maybe I'll see if I can set fire to a newspaper using a binocular.
' We've lost everything', say family after home destroyed by Nutella jar.
They have just been left with the shirts on their back after blaze sparked by sunbeams focused by a glass jar on a windowsill.
The damage is estimated at £250,000. Their pet Jack Russell terrier died.
The light was focused on part of the floor which had a dolls house which caught fire and flames spread to the roof.
The house looks basically just like a shell now.
This is not the first time I've heard of such an event.
One event was caused by a glass paperweight. And I've seen a magnifying make-up mirror concentrating the sun's rays producing great heat.
Also of course a magnifying glass and even spectacles can start a fire.
Maybe I'll see if I can set fire to a newspaper using a binocular.
Mark9473
Well-known member
There is a fundamental difference with the examples you quoted, and that is that with simple lenses or mirrors, the focal point lies outside the optic and therefore materials can be exposed to very concentrated radiation. In binoculars, the focal point lies within the instrument, at the location of the eyepiece field stop, and is therefore not accessible to outside materials.
You can set fire to a newspaper with a pair of binoculars if you unscrew the objective and use that by itself.
HighNorth
Well-known member
. Mark, I did wonder about that, whether using a 50 mm binocular with a newspaper to the rear of the eye lens, if the beam is still concentrated enough to set fire to the newspaper.
Is the field stop of the eyepiece the only place where the beam is concentrated, or as the beam travels through the eyepiece, are there other positions where the beam is concentrated enough to start a fire.
It is known that a 4 inch refractor or even a 3 inch refractor can crack the awful sun filters that were supplied to go on the rear of eyepieces. Whether the heat at this position is enough to set a newspaper on fire I don't know.
. Does it it depend on the size of the exit pupil? For instance, with a high magnification, the exit pupil might only be one millimetre across. If you place the newspaper here, I presume it can be set alight.
Is the field stop of the eyepiece the only place where the beam is concentrated, or as the beam travels through the eyepiece, are there other positions where the beam is concentrated enough to start a fire.
It is known that a 4 inch refractor or even a 3 inch refractor can crack the awful sun filters that were supplied to go on the rear of eyepieces. Whether the heat at this position is enough to set a newspaper on fire I don't know.
. Does it it depend on the size of the exit pupil? For instance, with a high magnification, the exit pupil might only be one millimetre across. If you place the newspaper here, I presume it can be set alight.
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. Regarding post 45.
The reason that I ask whether the beam is concentrated at other positions in an eyepiece is because of my concern with binoculars that have compound eyepieces. If the heat is concentrated on or near to a cemented pair, then the cement might fail. That is why I'm reluctant to use a high quality binocular for projection of the Sun onto white card.
The reason that I ask whether the beam is concentrated at other positions in an eyepiece is because of my concern with binoculars that have compound eyepieces. If the heat is concentrated on or near to a cemented pair, then the cement might fail. That is why I'm reluctant to use a high quality binocular for projection of the Sun onto white card.
Mark9473
Well-known member
Those awful eyepiece sun filters threaded onto the front of the eyepiece, not on the rear (no threads there). Thus with most eyepiece designs of the era, they were close to the eyepiece field stop and the scope's focal point.
I did some solar eyepiece projection last week, with my 80mm f/7 apo refractor. Even after more than an hour, the eyepiece housing stayed cold to the touch. I doubt there is a significant amount of heat inside with that kind of aperture, so I have no doubt that something like a 10x50 binocular will be fine. I wouldn't try it with a 25x100 though.
I did some solar eyepiece projection last week, with my 80mm f/7 apo refractor. Even after more than an hour, the eyepiece housing stayed cold to the touch. I doubt there is a significant amount of heat inside with that kind of aperture, so I have no doubt that something like a 10x50 binocular will be fine. I wouldn't try it with a 25x100 though.
. Hi Mark,
. The 1960s and 1970s refractors sometimes had these dangerous solar filters that screwed into the front of the eyepieces.
However, my 1957 3 inch brass refractor has this thread on the rear of the eyepieces. The actual eyepieces screwed into the eyepiece holder with RAS threads which I think are basically threaded 1.25 inch. I have here 4 eyepieces, three are complete and the outer rear thread is about 1.5 inch diameter. The solar filter and moon filter fitted onto the rear of this. These are Kelner, Orthoscopic and Huyghenian. The quarter inch eyepiece had so little eyerelief that I removed the rear part, which is missing now. I threw away the solar filter a long time ago.
It was mentioned here recently that some of the older Zeiss binoculars had solar filters that I think fitted on the rear of the eyepieces. I am rather surprised that Zeiss sold these.
The outer filter thread at the rear of the RAS eyepieces is 1 3/8 inch fine.
. The 1960s and 1970s refractors sometimes had these dangerous solar filters that screwed into the front of the eyepieces.
However, my 1957 3 inch brass refractor has this thread on the rear of the eyepieces. The actual eyepieces screwed into the eyepiece holder with RAS threads which I think are basically threaded 1.25 inch. I have here 4 eyepieces, three are complete and the outer rear thread is about 1.5 inch diameter. The solar filter and moon filter fitted onto the rear of this. These are Kelner, Orthoscopic and Huyghenian. The quarter inch eyepiece had so little eyerelief that I removed the rear part, which is missing now. I threw away the solar filter a long time ago.
It was mentioned here recently that some of the older Zeiss binoculars had solar filters that I think fitted on the rear of the eyepieces. I am rather surprised that Zeiss sold these.
The outer filter thread at the rear of the RAS eyepieces is 1 3/8 inch fine.
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. Today's Independent newspaper has an article on the solar eclipse on March 20. It is a rather strange and rather brief article.
It mentions that one has to take care using a camera. This would be correct if you are using an optical viewfinder and a long focus lens.
What is really strange is the following and I quote ' energy groups have voiced concerns about the power supply, given so much of it is now made up of solar energy. They have worked to head it off-but concerns remain that systems could see problems as people head into work and the power providers deal with the eclipse.'
This seems very strange indeed to me, what do they do when it is cloudy?
The article mentions that you need a solar filter to view the eclipse, and says that they will be available. But I think that this eclipse covers territory where 2 billion people live. If even 200 million tried to view it, I don't think that there are going to be, say, 100 million safe eclipse glasses available.
I quote again ' you might remember the warnings from 1999: never look straight into the Sun. If you do, you can permanently damage the back of your eye (it should say eyes) -where there are no pain sensors, so you won't even know that anything's gone wrong.'
' The key thing is to get some kind of dimming lens to watch the eclipse though. These will probably be readily available ahead of the event.' (I think that the first sentence here may give people the false impression to look through any piece of dark material, with inevitable multiple cases of eye injury).
I imagine, that governments will get into the act late and probably as in previous times be at a loss to advise properly.
It mentions that one has to take care using a camera. This would be correct if you are using an optical viewfinder and a long focus lens.
What is really strange is the following and I quote ' energy groups have voiced concerns about the power supply, given so much of it is now made up of solar energy. They have worked to head it off-but concerns remain that systems could see problems as people head into work and the power providers deal with the eclipse.'
This seems very strange indeed to me, what do they do when it is cloudy?
The article mentions that you need a solar filter to view the eclipse, and says that they will be available. But I think that this eclipse covers territory where 2 billion people live. If even 200 million tried to view it, I don't think that there are going to be, say, 100 million safe eclipse glasses available.
I quote again ' you might remember the warnings from 1999: never look straight into the Sun. If you do, you can permanently damage the back of your eye (it should say eyes) -where there are no pain sensors, so you won't even know that anything's gone wrong.'
' The key thing is to get some kind of dimming lens to watch the eclipse though. These will probably be readily available ahead of the event.' (I think that the first sentence here may give people the false impression to look through any piece of dark material, with inevitable multiple cases of eye injury).
I imagine, that governments will get into the act late and probably as in previous times be at a loss to advise properly.
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. A few further points.
If you're using a mirror to project the Crescent Sun onto a white screen or wall it helps if the room into which you are projecting is fairly dark, which enables you to use perhaps a 3 mm mirror rather than 5 mm, for a 5 m projection distance.
For a classroom, with a 10 m projection distance, one should try a 6 mm to 10 mm mirror. One should have the lights off in the classroom.
One should cover the flat hand mirror with anything, card or even paper.
It does not matter what shape the hole is in the card. It can be triangular, square or anything it will still give an image of the Sun on the wall.
You should have your back to the Sun when doing mirror projection.
Do not shine the beam of light into anybody's eyes.
Regarding which binoculars are safe to use for projection.
The Royal astronomical Society, which has good information suggests that telescope and binocular eyepieces can be damaged.
They make the point of not using unknown apparently dark Materials to view the Sun directly, because of the real dangers of very hot infrared radiation and high energy ultraviolet radiation.
However, an optical expert thinks that quality binoculars will be safe. Most eyepieces, he says, have their focal surface ahead of the glassware and are low enough power to have not too much concentration of the beam as it passes through. The antireflection coatings will help to reject heat absorption and the most damage can be done at the exit pupil which is well out of the way of eye cups; that's the place where a piece of paper can be ignited.
The gentleman did get a high quality eyepiece very hot but it survived. Bleaching of colour filters can be rapid and he says that he has badly damaged a polariser that didn't survive a F/15 solar beam.
He says that, the exit pupil was where the appalling solar filters were put and the thought of using one is horrible.
The Sun can do plenty of damage to telescopes left out under the blue skies. Shrouds burnt, sensors can be destroyed and all manner of expensive smells of burning!
So one gets different opinions.
Personally, I do not use very good binoculars for projection, particularly I would not leave them set up with the Sun shining through them. I do use the Docter 10x25 for brief projection. But I wouldn't use a good 10x42 or larger binocular.
It is up to the individual, to decide which binocular to use for projection.
On 2015 March 20 at 0931 UTC in the middle of England the sun's elevation is about 27° and the sun is in the south-east.
Projection using a colander is very simple, giving multiple solar images.
If you're using a mirror to project the Crescent Sun onto a white screen or wall it helps if the room into which you are projecting is fairly dark, which enables you to use perhaps a 3 mm mirror rather than 5 mm, for a 5 m projection distance.
For a classroom, with a 10 m projection distance, one should try a 6 mm to 10 mm mirror. One should have the lights off in the classroom.
One should cover the flat hand mirror with anything, card or even paper.
It does not matter what shape the hole is in the card. It can be triangular, square or anything it will still give an image of the Sun on the wall.
You should have your back to the Sun when doing mirror projection.
Do not shine the beam of light into anybody's eyes.
Regarding which binoculars are safe to use for projection.
The Royal astronomical Society, which has good information suggests that telescope and binocular eyepieces can be damaged.
They make the point of not using unknown apparently dark Materials to view the Sun directly, because of the real dangers of very hot infrared radiation and high energy ultraviolet radiation.
However, an optical expert thinks that quality binoculars will be safe. Most eyepieces, he says, have their focal surface ahead of the glassware and are low enough power to have not too much concentration of the beam as it passes through. The antireflection coatings will help to reject heat absorption and the most damage can be done at the exit pupil which is well out of the way of eye cups; that's the place where a piece of paper can be ignited.
The gentleman did get a high quality eyepiece very hot but it survived. Bleaching of colour filters can be rapid and he says that he has badly damaged a polariser that didn't survive a F/15 solar beam.
He says that, the exit pupil was where the appalling solar filters were put and the thought of using one is horrible.
The Sun can do plenty of damage to telescopes left out under the blue skies. Shrouds burnt, sensors can be destroyed and all manner of expensive smells of burning!
So one gets different opinions.
Personally, I do not use very good binoculars for projection, particularly I would not leave them set up with the Sun shining through them. I do use the Docter 10x25 for brief projection. But I wouldn't use a good 10x42 or larger binocular.
It is up to the individual, to decide which binocular to use for projection.
On 2015 March 20 at 0931 UTC in the middle of England the sun's elevation is about 27° and the sun is in the south-east.
Projection using a colander is very simple, giving multiple solar images.
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. Hi Mark,
I don't know if you mean today or March 20. Either way there is not much difference.
To all intents and purposes, one cannot take low elevation of the Sun into account.
In some countries such as Switzerland, at about 10,000 feet or 3000 m in the mountains I've experienced exceptionally strong sunlight even in the winter. This also applies to some countries at sea level that have very clean air.
The water vapour in the atmosphere also plays a part.
. But I have seen the sun at 5° elevation, which is absolutely blinding. This doesn't normally happen in southern England.
In England, with a lot of pollution and water in the atmosphere, the Sun doesn't seem quite so bright.
I normally use a welders glass 13 tilted as necessary to get the correct density. But I think the difference in densities is around 2.7 times for each shade. The scale is something ridiculous like the seventh root of 1000, I will look it up again.
. It is normally considered that a welders glass 14 should be used. However, welders glasses were not designed for solar viewing and some folks prefer not to use them, thinking that special solar filters are better.
I'm not so sure of this. Also I don't know whether there is a shelflife on a welders glass, or if it is affected by continual radiation either from arc welding or by the Sun.
In essence, I think that a low Sun might be around half the intensity of a high Sun.
Normally I think that high ultraviolet readings occur with the sun's elevation above about 45°.
Human beings have some protection against the Sun. Our eyebrows and recessed eyes protect us from a really high Sun.
Blinking is normally fast enough to prevent eye damage.
Averting our vision is another.
The pupil response is far too slow and anyway not very effective.
With the Sun at 20° elevation even a welders glass 13 untilted is often not dense enough even in polluted England. I often have to tilt it slightly, which is why I use a larger size welders glass 13, which is sufficiently high vertically to allow tilting, without risking direct exposure to the sun.
The problems come when we deliberately stare at the Sun, as we are tempted to do with all the hype of solar eclipses. If there was no advertisement at all, few people would notice a partial Eclipse. But with modern communications really large numbers of people will be aware of such events.
We have to consider that normally the full moon is considered the brightest thing we should look at with direct vision.
The Sun is about 450,000 times brighter than this. If at a really low elevation it is 200,000 times brighter than the full moon, it is inevitable what will happen if somebody stares at the Sun.
The solar eclipse glasses, which meet British and European standards reduce the sunlight by about 100,000 times and this is considered good enough for three minutes continual exposure and intermittent exposure for the few hours of an eclipse. But they should not be used by persons who have had eye surgery or have eye disease.
I think they are considered to have a shelflife of five years if they're kept in their original wrapper in the dark.
But low elevation of the Sun is something that should not even be considered as providing any protection whatsoever.
I don't know if you mean today or March 20. Either way there is not much difference.
To all intents and purposes, one cannot take low elevation of the Sun into account.
In some countries such as Switzerland, at about 10,000 feet or 3000 m in the mountains I've experienced exceptionally strong sunlight even in the winter. This also applies to some countries at sea level that have very clean air.
The water vapour in the atmosphere also plays a part.
. But I have seen the sun at 5° elevation, which is absolutely blinding. This doesn't normally happen in southern England.
In England, with a lot of pollution and water in the atmosphere, the Sun doesn't seem quite so bright.
I normally use a welders glass 13 tilted as necessary to get the correct density. But I think the difference in densities is around 2.7 times for each shade. The scale is something ridiculous like the seventh root of 1000, I will look it up again.
. It is normally considered that a welders glass 14 should be used. However, welders glasses were not designed for solar viewing and some folks prefer not to use them, thinking that special solar filters are better.
I'm not so sure of this. Also I don't know whether there is a shelflife on a welders glass, or if it is affected by continual radiation either from arc welding or by the Sun.
In essence, I think that a low Sun might be around half the intensity of a high Sun.
Normally I think that high ultraviolet readings occur with the sun's elevation above about 45°.
Human beings have some protection against the Sun. Our eyebrows and recessed eyes protect us from a really high Sun.
Blinking is normally fast enough to prevent eye damage.
Averting our vision is another.
The pupil response is far too slow and anyway not very effective.
With the Sun at 20° elevation even a welders glass 13 untilted is often not dense enough even in polluted England. I often have to tilt it slightly, which is why I use a larger size welders glass 13, which is sufficiently high vertically to allow tilting, without risking direct exposure to the sun.
The problems come when we deliberately stare at the Sun, as we are tempted to do with all the hype of solar eclipses. If there was no advertisement at all, few people would notice a partial Eclipse. But with modern communications really large numbers of people will be aware of such events.
We have to consider that normally the full moon is considered the brightest thing we should look at with direct vision.
The Sun is about 450,000 times brighter than this. If at a really low elevation it is 200,000 times brighter than the full moon, it is inevitable what will happen if somebody stares at the Sun.
The solar eclipse glasses, which meet British and European standards reduce the sunlight by about 100,000 times and this is considered good enough for three minutes continual exposure and intermittent exposure for the few hours of an eclipse. But they should not be used by persons who have had eye surgery or have eye disease.
I think they are considered to have a shelflife of five years if they're kept in their original wrapper in the dark.
But low elevation of the Sun is something that should not even be considered as providing any protection whatsoever.
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. Never having tried the colander method of projection, I thought I should try it as it was a sunny day today.
I didn't know if we had one, so I tried the sink drainer that goes over the sinkhole. This has many holes.
. But I didn't have any luck.
Then I thought of using a tea strainer or tea infuser I think they're called, but I haven't done that yet.
Not being at home in the kitchen, I asked if we had a colander, and 2 were magically found.
I just tried one, and the reason it didn't work in the kitchen was that the projection distance was far too short at 1 m. The most I could move to was 2 m and the images of the Sun began to appear.
Measuring the holes, they are 5 mm across, so I think that I need to have a clear run of 5 to 7 m.
The bottom of the colander has seven holes, a central one and six equally spaced holes around it.
I will have to wait till the sun is in the right place so I can get the proper, much longer, projection distance.
Here's hoping.
P. S.
At 3 to 4 m projection distance, the sun's images are beginning to look quite reasonable.
I think that this distance would probably show the Crescent Sun quite well during the eclipse. For better resolution, if you have 5 to 7 m with a colander that has 5 mm holes one should get good results.
I suppose that different colanders have different size holes?
I didn't know if we had one, so I tried the sink drainer that goes over the sinkhole. This has many holes.
. But I didn't have any luck.
Then I thought of using a tea strainer or tea infuser I think they're called, but I haven't done that yet.
Not being at home in the kitchen, I asked if we had a colander, and 2 were magically found.
I just tried one, and the reason it didn't work in the kitchen was that the projection distance was far too short at 1 m. The most I could move to was 2 m and the images of the Sun began to appear.
Measuring the holes, they are 5 mm across, so I think that I need to have a clear run of 5 to 7 m.
The bottom of the colander has seven holes, a central one and six equally spaced holes around it.
I will have to wait till the sun is in the right place so I can get the proper, much longer, projection distance.
Here's hoping.
P. S.
At 3 to 4 m projection distance, the sun's images are beginning to look quite reasonable.
I think that this distance would probably show the Crescent Sun quite well during the eclipse. For better resolution, if you have 5 to 7 m with a colander that has 5 mm holes one should get good results.
I suppose that different colanders have different size holes?
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Here's a link to the NASA Eclipse Web Site and Solar Eclipse Path for the total solar eclipse of 20th March, coinciding with the new moon for March :
http://eclipse.gsfc.nasa.gov/SEgoogle/SEgoogle2001/SE2015Mar20Tgoogle.html
http://eclipse.gsfc.nasa.gov/SEgoogle/SEgoogle2001/SE2015Mar20Tgoogle.html
Howard220
Well-known member
I was going to post something on the thread, but couldn't find it.
Ah, it has moved to be a Sticky.
Earlier today, I noticed that there were three very small sunspots in a line just above the centre disc of the Sun.
. There may be more than three but that is all I could see in a properly filtered small instrument. There have been almost no sunspots for about a week now. This may mean that in one rotation of the Sun, namely on March 20 there will be almost no sunspots. However, new sunspots may appear.
At about 1345 UTC today I tried projecting the sun's image using a Kowa TS-502 straight through spotting scope. This is lightweight and is I think 20×50. I normally use it handheld.
Handheld, in the kitchen, it produced a nice large image of the Sun on the kitchen wall, which is whitish, at a projection distance of 50 to 70 cm. But I could not see the sunspots. Also, it was difficult to locate the Sun handheld.
So I put it on an old Stitz versatile tripod that I have.
It was easy to locate the Sun and the image was quite good although there were differing colours at the top and the bottom of the image at the Sun's limb. But this is not objectionable.
Focusing it carefully, with the scope on the tripod, I could only get a projection distance of about 50 cm, I could see the short line of 3 or possibly more sunspots. They are very small and the resolution is not that great, but I was pleased that I can see the sunspots. This was through double glazing, and the kitchen table is in the way.
For viewing the Crescent Sun during the partial Eclipse, the image will be very good indeed. A group of people could see it, but not a whole classroom unless the projection distance was increased to several metres and the classroom would need to be pretty dark to see the large image of the Sun.
In the interests of science, and so you don't have to repeat this, I put the back of my hand at the exit pupil. It hurts!
Then I got a standard household safety match and put this near to the exit pupil. I was aware that maybe if it ignited it might damage or put marks on the eye lens of the eyepiece. This second hand spotting scope is not expensive so I was prepared to risk it.
After a few seconds, smoke started coming from the head of the match, but unfortunately in about 20 seconds or less the clouds rolled over. So the jury is out as to whether the match would ignite. I suppose it may take a bit more heat to ignite a newspaper. There was a film, I think called Fahrenheit 451? I don't know if I got the number right. Perhaps this is the temperature at which paper ignites. Although I suppose it varies.
So projection, using either an old astronomical refractor telescope without plastic parts, or maybe a small spotting scope, gives good results. But I would not leave this set up for tracking the Sun, as then the heat buildup might crack something, or possibly melt or burn something. I would not want the cement in eyepiece elements to fail.
Ah, it has moved to be a Sticky.
Earlier today, I noticed that there were three very small sunspots in a line just above the centre disc of the Sun.
. There may be more than three but that is all I could see in a properly filtered small instrument. There have been almost no sunspots for about a week now. This may mean that in one rotation of the Sun, namely on March 20 there will be almost no sunspots. However, new sunspots may appear.
At about 1345 UTC today I tried projecting the sun's image using a Kowa TS-502 straight through spotting scope. This is lightweight and is I think 20×50. I normally use it handheld.
Handheld, in the kitchen, it produced a nice large image of the Sun on the kitchen wall, which is whitish, at a projection distance of 50 to 70 cm. But I could not see the sunspots. Also, it was difficult to locate the Sun handheld.
So I put it on an old Stitz versatile tripod that I have.
It was easy to locate the Sun and the image was quite good although there were differing colours at the top and the bottom of the image at the Sun's limb. But this is not objectionable.
Focusing it carefully, with the scope on the tripod, I could only get a projection distance of about 50 cm, I could see the short line of 3 or possibly more sunspots. They are very small and the resolution is not that great, but I was pleased that I can see the sunspots. This was through double glazing, and the kitchen table is in the way.
For viewing the Crescent Sun during the partial Eclipse, the image will be very good indeed. A group of people could see it, but not a whole classroom unless the projection distance was increased to several metres and the classroom would need to be pretty dark to see the large image of the Sun.
In the interests of science, and so you don't have to repeat this, I put the back of my hand at the exit pupil. It hurts!
Then I got a standard household safety match and put this near to the exit pupil. I was aware that maybe if it ignited it might damage or put marks on the eye lens of the eyepiece. This second hand spotting scope is not expensive so I was prepared to risk it.
After a few seconds, smoke started coming from the head of the match, but unfortunately in about 20 seconds or less the clouds rolled over. So the jury is out as to whether the match would ignite. I suppose it may take a bit more heat to ignite a newspaper. There was a film, I think called Fahrenheit 451? I don't know if I got the number right. Perhaps this is the temperature at which paper ignites. Although I suppose it varies.
So projection, using either an old astronomical refractor telescope without plastic parts, or maybe a small spotting scope, gives good results. But I would not leave this set up for tracking the Sun, as then the heat buildup might crack something, or possibly melt or burn something. I would not want the cement in eyepiece elements to fail.
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What a coincidence!
Yes, that's right.
Solar eclipse, new moon
Lunar eclipse, full moon
Sometimes it doesn't hurt to point out the obvious, particularly for the benefit of younger readers. :t:
