tom thinks

date 2000-10-22:17:22

Poem A jay flies by laconiclly
Falling sideways on the breeze
While a mist of cedar waxwings
Flash yellow in the sun
Echoing the linden leaves
Now yellowing with fall
That hummed two months ago
With the roar of bees
Getting unexpected pollen
So late in summer

Play I am an opportunist, and today I had an opportunity.
I read in an amateur astronomy magazine that there will be a partial eclipse of the sun on Christmas day that will be visible over most of North America. By a typical perversity of nature it'll hardly take away any light from sun-drenched Southern California, but up here in Kingston, where sunlight is a rare commodity, it'll block about 60% of the sun around 12:30 pm, assuming that it's up by then so near Mid-Winter's Day.
Alex and I were home alone this afternoon, so it looked like a fun project to build a solar telescope, which we proceeded to do. The first thing to remember when dealing with this sort of thing is NEVER look at the sun with the naked eye ESPECIALLY during an eclipse!.
Normally, the sun is so bright that it hurts to look at it, but when part of the solar disk is covered the total brightness is lower, so the eye's normal reflexes are fooled and there's no desire to look away. But the maximum brightness is the same -- the part of the disk that is uncovered will blast the part of the retina of your eye that sees it with so much light that it sets off a kind of chemical chain reaction that can produce total blindness an hour or so later. Every time there's an eclipse of the sun a few people, mostly children, are blinded, which is a fully preventable tragedy.
There are lots of good ways to look at the sun without risk. Welder's goggles are one way -- only the very darkest are safe to use, and you should consult with an expert before using any -- but ordinary sunglasses will not do. One simple way that may be safe is to look at the refection of the sun in a sheet of glass, like a window or car wind-shield. I observed the annular eclipse we had a few years ago this way, although there is some risk involved -- if the windshield is angled wrong, or has been coated to make it reflective, you could be putting your eyes at risk.
The safest way, and the only way I recommend, is to use a pin-hole camera, which is what Alex and I made today. We started very simply, taking a square of corrugated cardboard and cutting a hole in it about an inch square. We taped a bit of thin cardboard over the hole and put a pin-hole in it; the corrugated cardboard was too thick to put the hole in itself.
The sun was bright and as high as it gets this far into fall, and we tried to see something by holding the cardboard up a foot or two away from the front wall of the house. It didn't work.
This is fairly typical of first attempts at anything. The square of cardboard was too small, and the pinhole was too small, and there was way too much ambient light. So I reamed out the pinhole a bit with my knife. The hole doesn't have to be round, you understand; I once observed a partial eclipse of the sun in Passadena by looking at the shadow of a palm tree, because anywhere the fronds made a small apperture that let the sun through a tiny cresent could be seen projected on the sidewalk. It wasn't the best helioscope ever seen, but it was certainly the most opportunistic.
With the bigger hole, and by standing in the entrance to the garage where there was a bit of shade for our eyes, we could just see a small eliptical spot cast by the sun in the shadow of the cardboard square. It was eliptical because the sun is only about 30 degrees above the horizon at this time of year, at most, and we were therefore projecting the image onto the concrete floor of the garage at a pretty steep angle, and the laws of trigonometry were doing the rest.
But we'd demonstrated the basic idea, which is what I wanted to show Alex, who is eight. We then got more ambitious: I wanted to build a better helioscope, something with more magnification and higher resolution. The magnification of a pin-hole camera is determined by the distance between the pin-hole and the surface where the iamge forms, and the resolution is determined by the size of the pin-hole. The smaller the hole, the higher the resolution, but the dimmer the image.
As it happens, there was a box about six inches square and six feet long that the patio umbrella I smashed the patio table with came in. With liberal use of the handy-man's secret weapon (duct tape) we sealed up both ends and cut a hole in one end that would accomodate a small slip of thin cardboard with the pin-hole in it, and we taped a bit of cardboard with a fairly large hole, made by a three-hole punch, across it. There was then only the question of how to see the image.
My first thought was a kind of eye-piece made from a cardboard tube, but that didn't work out so well because I didn't think it had the field of view required. When I tried it later, as well, it turned out that the cardboard tube I wanted to use didn't have thick enough walls to really block the light.
Making things properly light-tight is an art -- having worked on projects where we wanted to detect one photon at a time, I can say that when Shakespeare wrote: "There is no darkness but ignorance" he was dead on the mark. One of my senior colleagues used to go into dry goods stores, ask for black fabrics and then put various samples over his head to access their opacity. The human eye is a pretty sensitive photo-detector, and this is a pretty good way of determining which materials are worth further testing.
I cut a hole in the side of the box near the end where the image would form, away from the pin-hole, and when I put my face up to it I could see a lot of places where the cardboard had gaps and holes. A little more work with duct tape patched the worst of it, and I then built a small baffle out of corrugated cardboard you could put your face against to block out most of the ambient light.
Our first attempt to use the helioscope was a total failure, until Alex pointed out that I was aiming it at the overhang of the roof -- inside the house there just wasn't enough room to get both the position and angle right to see the sun with it. So we repaired to the front step, where I rested it on my knees and waved it around in the general direction of the sun. I could see a diffuse glow in some directions, which I took to be evidence of more light leakage until a bright spot about half an inch in diameter hove into view. I'd found the sun! It was almost blinding to my partly dark-adapted eyes, and I could pull my face well away from the view-hole and still see it clearly, so Alex and I could look at it together.
We later made a couple of further modificatations -- a white sheet of paper in the end of the box for the image to fall on, which made it brighter than the dull brown cardboard. And a way of slipping other bits of cardboard with smaller appertures over the big hole, so we could get crisper images at the cost of some brightness. To use the dimmest I had to find the sun first, then get Alex to put the small apperture in place while I held the 'scope steady, then get out of the way so he could have a look.
A follow-on project will be to figure out how small a hole we need to resolve sun-spots, which I've always wanted to be able to see. There is a really big helioscope on Mount Wilson, above Passadena, which casts an image about a foot in diameter, but I the tower it's on is probably close to 100 feet high, which is a bit ambitious for me.
This is one of the real priviledges of a scientific education -- the opporunity to experience science as play. This is too often lost in the modern academic environment, where the pressure to publish dominates everything. The kids and I are reading Tom Sawyer at bedtimes right now, and Mark Twain's observation that work is what we are obliged to do and paid for, and play is what we do for our own pleasure, is as fresh as ever. The same thing, done under different circumstances, might well be work.
Leaving academia for industry was excruciatingly hard, but one of the real benefits that I'm realizing even more now thanks to the touch of my Muse, has been the re-discovery of play, the opportunity to take these moments of joy with my children, beneath the autumn sun, where I do things not for money but for love.

Creatures I forgot to mention something at the end of my conversation with ducks. I was walking back along the dock when a duck off to my left began to quack in time with my steps: step/quack, step/quack.
A family of ducks to my right seemed much impressed with this, and the matriarch began to quack in time also: step/qquuaacckk, step/qquuaacckk, step/qquuaacckk! After a few beats they drifted out of time with me, until they were quacking against the beat of my steps: syncopated ducks, in stereo.

Find Enlightenment

date	2000-10-22:17:22
Poem	A jay flies by laconiclly Falling sideways on the breeze While a mist of cedar waxwings Flash yellow in the sun Echoing the linden leaves Now yellowing with fall That hummed two months ago With the roar of bees Getting unexpected pollen So late in summer
Play	I am an opportunist, and today I had an opportunity. I read in an amateur astronomy magazine that there will be a partial eclipse of the sun on Christmas day that will be visible over most of North America. By a typical perversity of nature it'll hardly take away any light from sun-drenched Southern California, but up here in Kingston, where sunlight is a rare commodity, it'll block about 60% of the sun around 12:30 pm, assuming that it's up by then so near Mid-Winter's Day. Alex and I were home alone this afternoon, so it looked like a fun project to build a solar telescope, which we proceeded to do. The first thing to remember when dealing with this sort of thing is NEVER look at the sun with the naked eye ESPECIALLY during an eclipse!. Normally, the sun is so bright that it hurts to look at it, but when part of the solar disk is covered the total brightness is lower, so the eye's normal reflexes are fooled and there's no desire to look away. But the maximum brightness is the same -- the part of the disk that is uncovered will blast the part of the retina of your eye that sees it with so much light that it sets off a kind of chemical chain reaction that can produce total blindness an hour or so later. Every time there's an eclipse of the sun a few people, mostly children, are blinded, which is a fully preventable tragedy. There are lots of good ways to look at the sun without risk. Welder's goggles are one way -- only the very darkest are safe to use, and you should consult with an expert before using any -- but ordinary sunglasses will not do. One simple way that may be safe is to look at the refection of the sun in a sheet of glass, like a window or car wind-shield. I observed the annular eclipse we had a few years ago this way, although there is some risk involved -- if the windshield is angled wrong, or has been coated to make it reflective, you could be putting your eyes at risk. The safest way, and the only way I recommend, is to use a pin-hole camera, which is what Alex and I made today. We started very simply, taking a square of corrugated cardboard and cutting a hole in it about an inch square. We taped a bit of thin cardboard over the hole and put a pin-hole in it; the corrugated cardboard was too thick to put the hole in itself. The sun was bright and as high as it gets this far into fall, and we tried to see something by holding the cardboard up a foot or two away from the front wall of the house. It didn't work. This is fairly typical of first attempts at anything. The square of cardboard was too small, and the pinhole was too small, and there was way too much ambient light. So I reamed out the pinhole a bit with my knife. The hole doesn't have to be round, you understand; I once observed a partial eclipse of the sun in Passadena by looking at the shadow of a palm tree, because anywhere the fronds made a small apperture that let the sun through a tiny cresent could be seen projected on the sidewalk. It wasn't the best helioscope ever seen, but it was certainly the most opportunistic. With the bigger hole, and by standing in the entrance to the garage where there was a bit of shade for our eyes, we could just see a small eliptical spot cast by the sun in the shadow of the cardboard square. It was eliptical because the sun is only about 30 degrees above the horizon at this time of year, at most, and we were therefore projecting the image onto the concrete floor of the garage at a pretty steep angle, and the laws of trigonometry were doing the rest. But we'd demonstrated the basic idea, which is what I wanted to show Alex, who is eight. We then got more ambitious: I wanted to build a better helioscope, something with more magnification and higher resolution. The magnification of a pin-hole camera is determined by the distance between the pin-hole and the surface where the iamge forms, and the resolution is determined by the size of the pin-hole. The smaller the hole, the higher the resolution, but the dimmer the image. As it happens, there was a box about six inches square and six feet long that the patio umbrella I smashed the patio table with came in. With liberal use of the handy-man's secret weapon (duct tape) we sealed up both ends and cut a hole in one end that would accomodate a small slip of thin cardboard with the pin-hole in it, and we taped a bit of cardboard with a fairly large hole, made by a three-hole punch, across it. There was then only the question of how to see the image. My first thought was a kind of eye-piece made from a cardboard tube, but that didn't work out so well because I didn't think it had the field of view required. When I tried it later, as well, it turned out that the cardboard tube I wanted to use didn't have thick enough walls to really block the light. Making things properly light-tight is an art -- having worked on projects where we wanted to detect one photon at a time, I can say that when Shakespeare wrote: "There is no darkness but ignorance" he was dead on the mark. One of my senior colleagues used to go into dry goods stores, ask for black fabrics and then put various samples over his head to access their opacity. The human eye is a pretty sensitive photo-detector, and this is a pretty good way of determining which materials are worth further testing. I cut a hole in the side of the box near the end where the image would form, away from the pin-hole, and when I put my face up to it I could see a lot of places where the cardboard had gaps and holes. A little more work with duct tape patched the worst of it, and I then built a small baffle out of corrugated cardboard you could put your face against to block out most of the ambient light. Our first attempt to use the helioscope was a total failure, until Alex pointed out that I was aiming it at the overhang of the roof -- inside the house there just wasn't enough room to get both the position and angle right to see the sun with it. So we repaired to the front step, where I rested it on my knees and waved it around in the general direction of the sun. I could see a diffuse glow in some directions, which I took to be evidence of more light leakage until a bright spot about half an inch in diameter hove into view. I'd found the sun! It was almost blinding to my partly dark-adapted eyes, and I could pull my face well away from the view-hole and still see it clearly, so Alex and I could look at it together. We later made a couple of further modificatations -- a white sheet of paper in the end of the box for the image to fall on, which made it brighter than the dull brown cardboard. And a way of slipping other bits of cardboard with smaller appertures over the big hole, so we could get crisper images at the cost of some brightness. To use the dimmest I had to find the sun first, then get Alex to put the small apperture in place while I held the 'scope steady, then get out of the way so he could have a look. A follow-on project will be to figure out how small a hole we need to resolve sun-spots, which I've always wanted to be able to see. There is a really big helioscope on Mount Wilson, above Passadena, which casts an image about a foot in diameter, but I the tower it's on is probably close to 100 feet high, which is a bit ambitious for me. This is one of the real priviledges of a scientific education -- the opporunity to experience science as play. This is too often lost in the modern academic environment, where the pressure to publish dominates everything. The kids and I are reading Tom Sawyer at bedtimes right now, and Mark Twain's observation that work is what we are obliged to do and paid for, and play is what we do for our own pleasure, is as fresh as ever. The same thing, done under different circumstances, might well be work. Leaving academia for industry was excruciatingly hard, but one of the real benefits that I'm realizing even more now thanks to the touch of my Muse, has been the re-discovery of play, the opportunity to take these moments of joy with my children, beneath the autumn sun, where I do things not for money but for love.
Creatures	I forgot to mention something at the end of my conversation with ducks. I was walking back along the dock when a duck off to my left began to quack in time with my steps: step/quack, step/quack. A family of ducks to my right seemed much impressed with this, and the matriarch began to quack in time also: step/qquuaacckk, step/qquuaacckk, step/qquuaacckk! After a few beats they drifted out of time with me, until they were quacking against the beat of my steps: syncopated ducks, in stereo.