I have one that folds up to a "globe" of 3 rings and a plate with a movable genomehole 😂 to adjust for date and on the outer ring with latitude adjustable hanging. You hang it and turn it till the light points through the hole on the inside of the hour ring and you have time and true geographical North. I made a leather pocket so it fits on my wrist, so technically it is a wristwatch/compass
I made a 24 clock widget for my phone using a thing called Wx, and after I moved 0 to the bottom instead of the top, marked the position of the sun (near the hour hand), and sunrise + sunset, it's basically a digital sundial. I'd buy it but I don't know how to publish it 🤷
It just gave me an idea for a fun smartphone sundial app: with a very short shutter speed and a bit of image processing the front camera measures the direction of the sun; the accelerometer makes sure the phone is level; the magnetometer knows where magnetic north is; the gps chip knows latitude and longitude; and the 5G connectivity can download the latest lookup tables for all the necessary corrections. The app would thus be telling the time by using all of the phone's sensors and chips except the clock :)
Photographing the sun is _very dangerous_ without _certified_ protective gear for the eyes and will almost certainly damage the camera without an appropriate filter. Assuming both of these things are being used, it's a great idea, but I don't think the phone needs to be level. The face of a sundial doesn't need to be and with all the other data, the necessary adjustments can be made. The algorithm for finding the intersection of the line from the sun (assumed to be infinitely distant) through a point on the gnomon with a plane doesn't care whether the plane is vertical or horizontal. It only cares if there is an intersection, i.e., all of the points on the line can't also lie in the plane. I've implemented this algorithm and it's freeware, so you're welcome to use it, if you want to program this app (unless you'd rather do it yourself or use something else, of course). Admittedly less fun and interesting, but it would be possible to implement this without photographing the sun at all, because the position of the sun at any time is either known or can be calculated, especially if one is already using tables (a database) to look up corrections. In fact, it could be done for any location, which might make it fun and interesting again.
@@laurencefinston7036 thanks a lot But I think I'll stick to fantasy specs and a fictitious app (like the nonsensical phone specs that are a regular feature in the xkcd webcomic :)
That would be cool. It could either tell you the time directly as you said, or just get your and sun's position to put a simulated shadow on a face like this so you have to position the phone and add the corrections yourself!
Well that was cool. I'm from Connecticut and used to work with a guy from Ansonia. I also own a Poljot watch. It's interesting how important this state used to be.
This was interesting. I'd heard about portable sundials but never saw one before. In 2007 I did some work on sundials (available for free on the internet) and lately I've been working on the subject again (and the results will also be free and available on the internet). There are books in print on laying out sundials and they all describe graphical methods for doing this on paper. I figured out that it was much easier to do this in 3D and did that instead. (Someone knowledgeable about sundials confirmed that I was correct.) The old methods were developed before there were 3D graphics programs. They are similar in that sense to linear perspective, which is also much easier to do (and more accurate) with 3D points and matrix multiplication. The deviation of magnetic north from true north can be found in the Astronomical Almanac and Nautical Almanac for each year. The hour lines on the face of a sundial are simply the projections of the meridians of a sphere divided into 24 equal sections with 0 hours at position of the gnomon onto the face of the sundial. The gnomon points to the north pole of the celestial sphere, where the star Polaris is conveniently located. The sun travels across the sky from east to west on a circle called the ecliptic, which is the projection of Earth's orbit around the sun onto the celestial sphere. The ecliptic is rotated with respect to the celestial equator (and Earth's equator) by approx. 23.4° (the "obliquitiy of the ecliptic") and the whole sky seems to rotate about Polaris from east to west, taking the ecliptic along with it. The sun is also moving along the ecliptic from west to east, but not very fast, so in the course of a day, it doesn't appear to move very much. What a sundial tells you is true local solar time, which I think is much more interesting than mean solar time or clock time.
I do all of my sundial designs now using 3D models in Google SketchUp -- it's SO much easier than doing calculations, especially when you have a surface that isn't level or a vertical wall that doesn't face directly south. Those calculations are complicated and easy to screw up, but with a 3D model, you just need to be accurate with the orientation of your gnomon and your surface.
Love your videos! I keep a few slide rules in my classroom for helping students understand logarithms and have showed a few of your videos to students when we get to talking about old technology. This video gave me some ideas for my trig unit!
As always, quite interesting. Thanks. Your hint about the pole having moved since then might be related to the weakening magnetic field of Earth, also since about the same time, worth looking into.
I was at a museum recently and I got excited when I saw machines I knew from your channel there; a Burroughs calculating machine, Brunsviga, Addiator and most importantly the Curta! They even had Napier's Bones!
I thought this up back in high school! I was sure I was going to make a mint! Not surprised it was an idea who's time had already come. Still want to figure out how to build one.
These kinds of astronomical gadgets are neat and it's a shame we stopped using astronomy in our daily lives to do things ... We need to recognize where the cardinal points are , or to just look at the night sky , Knowing wich planet is out is also very nice , i remember watching the rings of saturn once ... It's a different type of mind blown compared to mathematical gadgets i feel : They show you quirks of our tought , These show you immense objects beyond our comprension on immense scales
Dang, I came into this thinking I needed a portable sundial, and left thinking I need a Poljot watch. Also why would you make a sundial and not include a sextant for determining latitude? Seems like an oversight that massively brings down the quality of the tool.
If you could buy pocket watches I might be in the market for one but the gross things that collect the sweat on your wrist are just awful. Also too small.
I had that exact model (well, it was actually my dad's, I "borrowed" it when I found it in a box in the attic) I used it a few times when I was in the Scouts. DST non-sense caused me to loose interest. It probably disappeared in one of my mom's cleaning purges.
Strictly speaking, a gnomon doesn't have to point toward the celestial north pole. Any point between the sun and the plane of the dial will cast a shadow on the latter. For a usable sundial, it has to be within the perimeter of the dial, of course. It's all about projections and intersections of lines with planes and planes with other planes. A point suspended in space cannot be said to "point" in any direction, north or otherwise. Some sundials have a hole in the gnomon and use a point of light instead of a shadow for time-keeping. If I recall correctly, the point of having the gnomon point north is so the shadow of the entire gnomon will correspond with the same hour lines every day of the year. However, I'm a bit rusty on the details and have to review how this works. Another poster brought up the issue of clockwise and counter-clockwise, or widdershins and, er, shins (?), if you prefer. According to my understanding, it doesn't really apply to sundials: From any location on Earth, the celestial sphere appears to rotate from east to west. If I look north, it appears to rotate counterclockwise. If I turn around and face south, it appears to rotate clockwise. If I face due east, it appears to rotate from front to back, over my head, and if I face due west, then from back to front over my head. This doesn't depend on the hemisphere. I found this confusing while working on a couple of recent animations (using technical drawings) on this subject, but that would seem to be the way it works.
If the gnomon points directly north (and upward), the shadow of the entire gnomon will be at its thinnest at noon every day of the year, regardless of the declination of the sun. It will just be the thickness of gnomon. At every other time, the shadow of a gnomon will be triangular, assuming a triangular gnomon. I believe that the origin of the hour lines will always be the point of intersection of the line from the tip of gnomon to the celestial north pole with the plane of the face of the dial, regardless of the shape or orientation of the gnomon itself. If the gnomon has some other shape or is oriented differently, the shadow will just be triangular and the minimum width of the shadow will come at the time when it's aligned with the rays of the sun. In the worst case, part of the gnomon may prevent the sun from falling on the tip, rendering the sundial useless for the times when this happens. The sun is so far away that the rays from the sun are very nearly parallel. As a consequence, the vector for the direction of the sun's rays will be the same for any point on Earth. In fact, if we consider the sun to be infinitely far away, then it will be the same for any point at all. The problem is, that the coordinate system used for describing the vector is different, depending on the location. The celestial poles and equator are the same for every point on Earth, but the zenith, nadir and horizon are different for every point on Earth and the zenith and the horizon are the data that we can acquire directly with a reasonable amount of effort. Longitude is a different matter. If we didn't consider the sun to be infinitely far away, it probably wouldn't be possible to calculate the angles and distances for the rays of the sun, because the angles would be very small and the distances very large. If the resulting numbers are even representable at all in a computer or calculator, it would not be possible to calculate with them as a consequence of the way real numbers are represented in a computer. They would not be commensurable.
@8:15 they have no respect! 💁🙈🙈🙈 ..... Excellent video. I'm pretty quirky and use things like this because I love old skool tech, so yes, i would definitely use one in public if i had it. I was an amateur prospector years ago and used a compasses and stick sundial for my cartography... luckily no one contracted me to make a map for them as it already took me three hours to set up and map out the Bellingham waterfront (while cheating with a Delorme topo map for backup)! 😝😝😝
😳 Magnetic North MOVES?! but what about the constancy of the solar system? What about the BigG?! What about Laws of The Universe?! 😅 That’s some nifty little gadget you got there. Why do these things have such interesting backstories? I mean, Stalin? WOW !!
Very interesting! Better than what I was looking at before- interestingly it shows almost no change in CT where I am across the last century. (Significant changes all around, just not where I am.)
@@ChrisStaecker Over here in California, we have about a 5° declination since the 20's. I need to see if I can get my hands on one of these to see how it fares on the west coast. Even with it being off by 10 minutes that's still incredibly impressive.
Nice that the UK versions went as far as Aberdeen and Inverness at 57 deg N, but I feel like sundials would be strictly a summer-only business round here
The area where the gnomon attaches to the base might be a bit damaged causing some of the inaccuracies. Just a little bend in the metal would move the tip. You might be able to test that at two different times of day with the shadow on both sides of the slot. Let’s say 10am and 2pm. If it’s bent to the left, both measurements should be a bit early. Right, late. If it’s dented down some, left should show late, right early. . . I think.
Did you know that compass variation changes over time? It’s because the molten iron core in the center of the earth that the magnetic needle is attracted to is liquid, and moves around a little. At New York City it’s no longer 10º; it’s currently 13º.
This exact model was heavily promoted to the Boy Scouts of the time so they're not terribly rare. And historically, time has always been referenced to the sun, so these can be quite accurate once you factor in all the variables exactly, which this only does roughly. A bit less than useful on cloudy days and at night, but interesting anyway.
An interesting thing about laying out sundials the way I described in my previous post is that you can't just calculate the position of the sun (azimuth and elevation) and draw a line from a point representing it through the tip of the gnomon to find the intersection with the face of the dial. The sun is assumed to be infinitely far away, so you have to "work backwards": That is, you have to find the vector `v' from the point `b' at the base of the gnomon (where it intersects with the dial, that is, the origin of the hour lines) to the sun, add `v' to the point `t' at the tip of the gnomon to get point `p' and find the intersection of the line `tp' with the plane of the face. That will be the tip of the shadow for any given moment (during the day, of course). You can't use the base of the gnomon, because it lies in the plane of the face of the sundial, so no shadow.
I have one of these .... In The Original Box (and with the directions). I believe the company made 5 of them for various places in the world you might happen to be traveling in and need to know the time on a sunny day.
Honestly it’s pretty impressive. Spend a minute or two to set it up, get the correct time to within about 10-15 minutes no matter where you are in the (continental) u.s.
FYI : We had reliable portable time telling devices since 1735 when John Harrison invented the chronometer but the first "pocket watch" was invented in 1510 by Peter Henlein. In 1920 the "portable sundial" would've been seen as a educational toy. (I have mixed opinions of the educational toys that we have now.)
I suspect if you used proper modern Declination (aka variation) Variation 13.23° = 13.03°W (WMM2020 magnetic declination) + (4 = 2024-2020) * 0.05° annual change [values for BDR, nearest airport], and for other values took the mean of NYC and HFD values {assuming BDR isn't on the lid}, it'd do even better. You are quite a ways east of the NYC meridian as well as north of Manhattan. The brass case might even be protecting the compass from the ironwork of your deck table - but best practice would have it on wood or other non ferrous surface. Also, if there is a bubble of air in the compass, use that to assure it's perfectly level, or otherwise a small bubble level can verify it's level.
I used to collect slide rules but when all of my things were stolen back in 2014 I quit gathering things that are apparently being collected for others. Somebody stole my scooter last week. I had 9240 miles on it after 3 years. Almost made it to 10k. I probably have the record for number of two wheeled vehicles that have been stolen from me. This makes 8. I think my aura is different than other people or something. I guy tried to hit me on it just a few weeks earlier. I should make a 3D version with replaceable rings to associate with a region. Make a really elaborate design and post it on the 3D sites.
Actually is probably more accurate than you calculated. Reality is declination changes on a regular basis. So you used the 10 on the "VAR". Current declination for NY is 13 degrees. So recalculating for that might change it more accurately.
*Thank You* WHY these Beautiful Buildings are allowed to be 'Nothing' to others? time will tell: Lacking Respect for History, Honor, Teach Skill, Fail to Stand by your work, Speak NO *TRUTH,* ... we all will be Feeling the *HtURT.*
It's neat to think the sundial requires the gnomon to be parallel to the axis of the Earth. I've been looking for a sundial with an adjustable gnomon for years. Do you think Amazon ships from the past?
Be aware that for this type of horizontal dial, both the angle of the gnomon AND the layout of the hour lines depend on the latitude. (This dial sort of fudges that by having 3 dials, but if you're not on one of those latitudes, it won't quite be accurate.) However, a little known fact is that if a horizontal sundial is properly laid out for a given latitude, you can use it at a different latitude, by simply tilting it north or south until the gnomon is at the angle corresponding to your latitude (i.e. make it parallel to the Earth's axis). Both the gnomon and the dial face will then be parallel with a level dial at the design latitude, so it will show the correct solar time as if it were at that latitude. For example, if you know your dial was designed for 40 N, you can use it at 45 N by just tilting it 5 degrees southward.
Accidental collection- I got the wooden one randomly and liked the concept. Then I got the black one because I thought I would like it better, but I didn't really. Then finally got the Ansonia as the ideal form. But they're small and cheap so more the merrier?
The fact that Chris knew so much about this topic but indicated he wasn't sure about what an acceptable margin of error for a sundial is made me curious about it. Is 15-20 minutes excellent?
@@burlapknapsack No, certainly not. A minute would be excellent, in my opinion, and two very good. The first thing to do would be to set it up so that it shows true solar noon and then check whether the hour lines are correct. If not, you can forget it. However, given the general impression of quality of this instrument, I would expect that they would be. The correct values for the latitude and longitude would have to be used and the gnomon would have to be checked and, if necessary, adjusted. After 97 years and presumably decades of use and/or neglect, it may well need adjusting. Of course, the current value of the deviation of magnetic from true north would have to be found and the correction applied. Astronomical yearbooks give the values for true solar noon (culmination of the sun), sunrise and sunset for a few days in every month. Otherwise, they can be calculated. I don't know the equations off-hand or I'd write them here. This is what I'm currently working on. They involve "The Equation of Time" and the "Julian Date" and aren't that difficult (it's just arithmetic).
Some brasso and scotchbrite and elbow grease should help fight that corrosion. Or if you have want you could could clean and polish the whole thing. But scrubbing off that writing from 1927 would be a shame
Given the age of that sundial, the correction for true north is no longer right. Get a current aviation sectional chart to find out the correct values for your location!
I just read the instructions and the result can only be rough approximation. To get an accurate result, the true values of latitude and longitude must be used and an accurate time correction must be applied. I haven't checked this, but it appeared that the gnomon can be positioned continuously, i.e., not in steps. The instructions are very terse and don't go into the theory or how to get a more accurate reading. In the northern hemisphere, the gnomon must point to the celestial north pole, where the star Polaris is located. If the sundial was at the north pole, this would be straight up. At Ansonia, Connecticut, 41°20′36″N 73°04′07″W, it would have to be pointed to the north (true north, i.e., magnetic north with the correction for the deviation from true north applied), and angled upward at an angle of 41°20′36″. This is the angle with respect to the plane tangent to the Earth at this location that corresponds with the direction toward the celestial north pole. In the southern hemisphere, you would have to point the gnomon at the celestial south pole and at the equator, well, you're out of luck, at least as far as this method is concerned. The correct longitude, in this case, 73°04′07″W, must be used because otherwise the time values will be off. The sun appears to move from east to west across the sky and culminates at true local solar noon. This is, in fact, the definition of true local solar noon: it's whenever the sun culminates. Since the earth is rotating, it culminates earlier the further east you go, so it will be noon earlier at 70° W and later at 80° W. That is, at a given moment, it's later in the east than in the west. Clearly, to get an accurate time value, the correct longitude must be used. Of course, the surface the sundial is placed on must be level. Sundials can have oblique dials, but this affects the placement of the hour lines. And don't forget to wind it up!
So you REALLY tried to use a magnetic compass sitting on a cast iron patio table grate? Amazing that you were within 10 minutes. If you learn anything much about Navigation and Astronomy, you will realize that a sundial, properly constructed, along with accurate and precise data and correction calculations, can easily give accuracy to well under a minute. The only problem is that from the moment that someone asks you for the time, to the moment that you reply with the precisely and accurately corrected time indicated by the sundial, several minutes can pass, and so you will want a hack watch to record elapsed time, to quickly add to the found time, for the updated solution. The simple path to accuracy would be to pre-compute the time for a shadow position a few minutes into the future, and then the instant that the shadow hits the selected mark or position, you then have the time, right on the money.
Just a gray void for a thumbnail? Yesterday it was the actual sundial... are you doing A/B Tests? The current thumbnail is NOT specially click-urgency-generating... 🤣
I'm using this new UA-cam feature: support.google.com/youtube/answer/13861714?hl=en_ID Maybe some glitch on their end? Or your browser/app didn't load it right. I think all 3 thumbnails are working OK.
It may well be of interest to about 1% of those fascinated by old horology. Beyond that it's useless. How are you going to wear it? What will you do when daylight saving comes in. If you tried to explain all this today, you'll come across as a bore.
You don't wear it- you put it in your pocket. When daylight saving comes in, you add an extra hour. I tried to explain all this today- did I come across as a bore?
"pocket sundial" feels like a flinstones gag, I love it!
I have one that folds up to a "globe" of 3 rings and a plate with a movable genomehole 😂 to adjust for date and on the outer ring with latitude adjustable hanging. You hang it and turn it till the light points through the hole on the inside of the hour ring and you have time and true geographical North.
I made a leather pocket so it fits on my wrist, so technically it is a wristwatch/compass
I made a 24 clock widget for my phone using a thing called Wx, and after I moved 0 to the bottom instead of the top, marked the position of the sun (near the hour hand), and sunrise + sunset, it's basically a digital sundial. I'd buy it but I don't know how to publish it 🤷
@@aleisterlavey9716 Genome? I am 100% certain you mean gnomon. That's the shadow-casting provision (just a rod in the simplest case).
@@DerMarkus1982 yeah. Autocorrect is a female dog. 😅
That's because it was (or at least Fred had a sundial watch in one episode)
It just gave me an idea for a fun smartphone sundial app: with a very short shutter speed and a bit of image processing the front camera measures the direction of the sun; the accelerometer makes sure the phone is level; the magnetometer knows where magnetic north is; the gps chip knows latitude and longitude; and the 5G connectivity can download the latest lookup tables for all the necessary corrections.
The app would thus be telling the time by using all of the phone's sensors and chips except the clock :)
@@melainekerfaou8418 I approve
I love how you need to get the time for the GPS to work.
Photographing the sun is _very dangerous_ without _certified_ protective gear for the eyes and will almost certainly damage the camera without an appropriate filter. Assuming both of these things are being used, it's a great idea, but I don't think the phone needs to be level. The face of a sundial doesn't need to be and with all the other data, the necessary adjustments can be made.
The algorithm for finding the intersection of the line from the sun (assumed to be infinitely distant) through a point on the gnomon with a plane doesn't care whether the plane is vertical or horizontal. It only cares if there is an intersection, i.e., all of the points on the line can't also lie in the plane.
I've implemented this algorithm and it's freeware, so you're welcome to use it, if you want to program this app (unless you'd rather do it yourself or use something else, of course).
Admittedly less fun and interesting, but it would be possible to implement this without photographing the sun at all, because the position of the sun at any time is either known or can be calculated, especially if one is already using tables (a database) to look up corrections. In fact, it could be done for any location, which might make it fun and interesting again.
@@laurencefinston7036 thanks a lot
But I think I'll stick to fantasy specs and a fictitious app (like the nonsensical phone specs that are a regular feature in the xkcd webcomic :)
That would be cool. It could either tell you the time directly as you said, or just get your and sun's position to put a simulated shadow on a face like this so you have to position the phone and add the corrections yourself!
NO-ONE expects the Soviet Acquisition!
Nice job there, really good.
That Louisville pronunciation was a thing of beauty
Fantastic video! I loved the weird historical backstory.
Well that was cool. I'm from Connecticut and used to work with a guy from Ansonia. I also own a Poljot watch. It's interesting how important this state used to be.
This was interesting. I'd heard about portable sundials but never saw one before. In 2007 I did some work on sundials (available for free on the internet) and lately I've been working on the subject again (and the results will also be free and available on the internet). There are books in print on laying out sundials and they all describe graphical methods for doing this on paper. I figured out that it was much easier to do this in 3D and did that instead. (Someone knowledgeable about sundials confirmed that I was correct.) The old methods were developed before there were 3D graphics programs. They are similar in that sense to linear perspective, which is also much easier to do (and more accurate) with 3D points and matrix multiplication.
The deviation of magnetic north from true north can be found in the Astronomical Almanac and Nautical Almanac for each year.
The hour lines on the face of a sundial are simply the projections of the meridians of a sphere divided into 24 equal sections with 0 hours at position of the gnomon onto the face of the sundial. The gnomon points to the north pole of the celestial sphere, where the star Polaris is conveniently located. The sun travels across the sky from east to west on a circle called the ecliptic, which is the projection of Earth's orbit around the sun onto the celestial sphere. The ecliptic is rotated with respect to the celestial equator (and Earth's equator) by approx. 23.4° (the "obliquitiy of the ecliptic") and the whole sky seems to rotate about Polaris from east to west, taking the ecliptic along with it.
The sun is also moving along the ecliptic from west to east, but not very fast, so in the course of a day, it doesn't appear to move very much.
What a sundial tells you is true local solar time, which I think is much more interesting than mean solar time or clock time.
I do all of my sundial designs now using 3D models in Google SketchUp -- it's SO much easier than doing calculations, especially when you have a surface that isn't level or a vertical wall that doesn't face directly south. Those calculations are complicated and easy to screw up, but with a 3D model, you just need to be accurate with the orientation of your gnomon and your surface.
Needs an Addiator slapped on the back for making the calculations.
This is honestly super cool. I bet anyone proficient in reading sundials would pull this out as a party trick.
Love your videos! I keep a few slide rules in my classroom for helping students understand logarithms and have showed a few of your videos to students when we get to talking about old technology. This video gave me some ideas for my trig unit!
Gnomon is an island.
By the time you’ve calculated the time it’s later
As always, quite interesting. Thanks. Your hint about the pole having moved since then might be related to the weakening magnetic field of Earth, also since about the same time, worth looking into.
I was at a museum recently and I got excited when I saw machines I knew from your channel there; a Burroughs calculating machine, Brunsviga, Addiator and most importantly the Curta! They even had Napier's Bones!
Nice! Where was it?
That was a plot twist at the end I wasn't expecting.
4:15
From Kentucky, and appreciate the proper pronunciation of loovle
I thought this up back in high school! I was sure I was going to make a mint! Not surprised it was an idea who's time had already come. Still want to figure out how to build one.
The short was good but it wasn't quite long enough, this video takes the cake
These kinds of astronomical gadgets are neat and it's a shame we stopped using astronomy in our daily lives to do things ...
We need to recognize where the cardinal points are , or to just look at the night sky ,
Knowing wich planet is out is also very nice , i remember watching the rings of saturn once ...
It's a different type of mind blown compared to mathematical gadgets i feel :
They show you quirks of our tought ,
These show you immense objects beyond our comprension on immense scales
It's wild to see the radium dial ad on the last page of the manual.
I have a Poljot watch from the 70s and damn man do i love that watch ❤
This has got to be the coolest way to tell someone the time. "What time is it?" Give me second to figure it out and I'll tell ya.
Dang, I came into this thinking I needed a portable sundial, and left thinking I need a Poljot watch. Also why would you make a sundial and not include a sextant for determining latitude? Seems like an oversight that massively brings down the quality of the tool.
If you could buy pocket watches I might be in the market for one but the gross things that collect the sweat on your wrist are just awful. Also too small.
@@creamwobbly Sadly it seems they only made wristwatches.
By the way, couldn't help but notice your username. Are you a Wobbly, as in Bill Haywood?
I had that exact model (well, it was actually my dad's, I "borrowed" it when I found it in a box in the attic) I used it a few times when I was in the Scouts. DST non-sense caused me to loose interest. It probably disappeared in one of my mom's cleaning purges.
Strictly speaking, a gnomon doesn't have to point toward the celestial north pole. Any point between the sun and the plane of the dial will cast a shadow on the latter. For a usable sundial, it has to be within the perimeter of the dial, of course. It's all about projections and intersections of lines with planes and planes with other planes.
A point suspended in space cannot be said to "point" in any direction, north or otherwise. Some sundials have a hole in the gnomon and use a point of light instead of a shadow for time-keeping. If I recall correctly, the point of having the gnomon point north is so the shadow of the entire gnomon will correspond with the same hour lines every day of the year. However, I'm a bit rusty on the details and have to review how this works.
Another poster brought up the issue of clockwise and counter-clockwise, or widdershins and, er, shins (?), if you prefer. According to my understanding, it doesn't really apply to sundials: From any location on Earth, the celestial sphere appears to rotate from east to west. If I look north, it appears to rotate counterclockwise. If I turn around and face south, it appears to rotate clockwise. If I face due east, it appears to rotate from front to back, over my head, and if I face due west, then from back to front over my head. This doesn't depend on the hemisphere. I found this confusing while working on a couple of recent animations (using technical drawings) on this subject, but that would seem to be the way it works.
If the gnomon points directly north (and upward), the shadow of the entire gnomon will be at its thinnest at noon every day of the year, regardless of the declination of the sun. It will just be the thickness of gnomon. At every other time, the shadow of a gnomon will be triangular, assuming a triangular gnomon.
I believe that the origin of the hour lines will always be the point of intersection of the line from the tip of gnomon to the celestial north pole with the plane of the face of the dial, regardless of the shape or orientation of the gnomon itself. If the gnomon has some other shape or is oriented differently, the shadow will just be triangular and the minimum width of the shadow will come at the time when it's aligned with the rays of the sun. In the worst case, part of the gnomon may prevent the sun from falling on the tip, rendering the sundial useless for the times when this happens.
The sun is so far away that the rays from the sun are very nearly parallel. As a consequence, the vector for the direction of the sun's rays will be the same for any point on Earth. In fact, if we consider the sun to be infinitely far away, then it will be the same for any point at all. The problem is, that the coordinate system used for describing the vector is different, depending on the location. The celestial poles and equator are the same for every point on Earth, but the zenith, nadir and horizon are different for every point on Earth and the zenith and the horizon are the data that we can acquire directly with a reasonable amount of effort. Longitude is a different matter.
If we didn't consider the sun to be infinitely far away, it probably wouldn't be possible to calculate the angles and distances for the rays of the sun, because the angles would be very small and the distances very large. If the resulting numbers are even representable at all in a computer or calculator, it would not be possible to calculate with them as a consequence of the way real numbers are represented in a computer. They would not be commensurable.
I loved this. Wonderful.
Idiot customer: _"That's really cool! Does it have a backlight?"_
Merchant: _"No, why?"_
Idiot customer: _"I work night shift."_
Great video, as always - loved it!
I live in the southern hemisphere. Don't get me started on sundials and widdershins
I always love your videos
@8:15 they have no respect! 💁🙈🙈🙈
.....
Excellent video.
I'm pretty quirky and use things like this because I love old skool tech, so yes, i would definitely use one in public if i had it.
I was an amateur prospector years ago and used a compasses and stick sundial for my cartography... luckily no one contracted me to make a map for them as it already took me three hours to set up and map out the Bellingham waterfront (while cheating with a Delorme topo map for backup)! 😝😝😝
I can't believe you've gnomed me old chum
😳 Magnetic North MOVES?! but what about the constancy of the solar system? What about the BigG?! What about Laws of The Universe?! 😅
That’s some nifty little gadget you got there. Why do these things have such interesting backstories? I mean, Stalin? WOW !!
The Big G wrote the laws and things are acting accordingly lol
this channel's urbex era incoming
You have a great storytelling voice.
NOAA has a nice 2010 map of the US for magnetic declination.
Very interesting! Better than what I was looking at before- interestingly it shows almost no change in CT where I am across the last century. (Significant changes all around, just not where I am.)
@@ChrisStaecker Over here in California, we have about a 5° declination since the 20's. I need to see if I can get my hands on one of these to see how it fares on the west coast.
Even with it being off by 10 minutes that's still incredibly impressive.
Nice that the UK versions went as far as Aberdeen and Inverness at 57 deg N, but I feel like sundials would be strictly a summer-only business round here
The area where the gnomon attaches to the base might be a bit damaged causing some of the inaccuracies. Just a little bend in the metal would move the tip. You might be able to test that at two different times of day with the shadow on both sides of the slot. Let’s say 10am and 2pm.
If it’s bent to the left, both measurements should be a bit early. Right, late. If it’s dented down some, left should show late, right early. . . I think.
You need to add one, or two, extra minutes to the Sunwatch time, to compensate for how long it took to do all the mathematical calculations.
I have the same expanded metal top yard furniture. You have some cool things.
Yes, but probably not a good table to use with a compass.
Yes those shots were my first attempts- I quickly realized something was up and did the rest away from the table.
Did you know that compass variation changes over time? It’s because the molten iron core in the center of the earth that the magnetic needle is attracted to is liquid, and moves around a little. At New York City it’s no longer 10º; it’s currently 13º.
bro have I got a video for you
I have one of those, couldn't resist at $10.
This exact model was heavily promoted to the Boy Scouts of the time so they're not terribly rare. And historically, time has always been referenced to the sun, so these can be quite accurate once you factor in all the variables exactly, which this only does roughly. A bit less than useful on cloudy days and at night, but interesting anyway.
An interesting thing about laying out sundials the way I described in my previous post is that you can't just calculate the position of the sun (azimuth and elevation) and draw a line from a point representing it through the tip of the gnomon to find the intersection with the face of the dial. The sun is assumed to be infinitely far away, so you have to "work backwards": That is, you have to find the vector `v' from the point `b' at the base of the gnomon (where it intersects with the dial, that is, the origin of the hour lines) to the sun, add `v' to the point `t' at the tip of the gnomon to get point `p' and find the intersection of the line `tp' with the plane of the face. That will be the tip of the shadow for any given moment (during the day, of course). You can't use the base of the gnomon, because it lies in the plane of the face of the sundial, so no shadow.
Heck yeah! There should definitely be a historical marker.
Sadly, the magnetic heading for north can be wildly off depending on your location as well, which will throw in more errors.
God I wanna be the absolute irredeemable piece of shit that gets asked for the time and pull out this stuff.
He's gotta be a hell of a professor. LOL
Disney Hercules didn’t lie to us
I have one of these .... In The Original Box (and with the directions). I believe the company made 5 of them for various places in the world you might happen to be traveling in and need to know the time on a sunny day.
Nice! I didn't know there was an original box. I've heard there was also one for canada and one for australia, but I've never seen photos of those.
@@ChrisStaecker Will send you a photo
THE ORIGINAL
instructions
Honestly it’s pretty impressive.
Spend a minute or two to set it up, get the correct time to within about 10-15 minutes no matter where you are in the (continental) u.s.
When I was a kid I had a Casio watch.
It seems like a device that would be more practically used to set your mechanical watch by.
FYI : We had reliable portable time telling devices since 1735 when John Harrison invented the chronometer but the first "pocket watch" was invented in 1510 by Peter Henlein. In 1920 the "portable sundial" would've been seen as a educational toy. (I have mixed opinions of the educational toys that we have now.)
I suspect if you used proper modern Declination (aka variation) Variation 13.23° = 13.03°W (WMM2020 magnetic declination) + (4 = 2024-2020) *
0.05° annual change [values for BDR, nearest airport], and for other values took the mean of NYC and HFD values {assuming BDR isn't on the lid}, it'd do even better. You are quite a ways east of the NYC meridian as well as north of Manhattan. The brass case might even be protecting the compass from the ironwork of your deck table - but best practice would have it on wood or other non ferrous surface. Also, if there is a bubble of air in the compass, use that to assure it's perfectly level, or otherwise a small bubble level can verify it's level.
It's time!
I used to collect slide rules but when all of my things were stolen back in 2014 I quit gathering things that are apparently being collected for others. Somebody stole my scooter last week. I had 9240 miles on it after 3 years. Almost made it to 10k. I probably have the record for number of two wheeled vehicles that have been stolen from me. This makes 8. I think my aura is different than other people or something. I guy tried to hit me on it just a few weeks earlier. I should make a 3D version with replaceable rings to associate with a region. Make a really elaborate design and post it on the 3D sites.
Actually is probably more accurate than you calculated. Reality is declination changes on a regular basis. So you used the 10 on the "VAR". Current declination for NY is 13 degrees. So recalculating for that might change it more accurately.
watch to the end bro
I use the Crocodile Dundee method if I'm not in a calculating mood.
Before GPS how would you know where is the bus at? With this little gem. Great vid.
Now I have to get one, or make one 🤪
*Thank You* WHY these Beautiful Buildings are allowed to be 'Nothing' to others?
time will tell: Lacking Respect for History, Honor, Teach Skill, Fail to Stand by your work, Speak NO *TRUTH,* ... we all will be Feeling the *HtURT.*
It's neat to think the sundial requires the gnomon to be parallel to the axis of the Earth. I've been looking for a sundial with an adjustable gnomon for years. Do you think Amazon ships from the past?
Be aware that for this type of horizontal dial, both the angle of the gnomon AND the layout of the hour lines depend on the latitude. (This dial sort of fudges that by having 3 dials, but if you're not on one of those latitudes, it won't quite be accurate.) However, a little known fact is that if a horizontal sundial is properly laid out for a given latitude, you can use it at a different latitude, by simply tilting it north or south until the gnomon is at the angle corresponding to your latitude (i.e. make it parallel to the Earth's axis). Both the gnomon and the dial face will then be parallel with a level dial at the design latitude, so it will show the correct solar time as if it were at that latitude. For example, if you know your dial was designed for 40 N, you can use it at 45 N by just tilting it 5 degrees southward.
Gnomon!
Pretty cool. If you carried a slide ruler also. Could get really accurate?
I gave my father's one to my son. It's from 1920s
You own three?!?
Accidental collection- I got the wooden one randomly and liked the concept. Then I got the black one because I thought I would like it better, but I didn't really. Then finally got the Ansonia as the ideal form. But they're small and cheap so more the merrier?
I’m always amazed by the things that people own that I’ve never even heard of.
@@stephenfreeborn You of all people! Hah-
I am fairly confident this sundial could be set up to get quite accurate results.
The fact that Chris knew so much about this topic but indicated he wasn't sure about what an acceptable margin of error for a sundial is made me curious about it. Is 15-20 minutes excellent?
I’d like to know!
@@burlapknapsack No, certainly not. A minute would be excellent, in my opinion, and two very good.
The first thing to do would be to set it up so that it shows true solar noon and then check whether the hour lines are correct. If not, you can forget it. However, given the general impression of quality of this instrument, I would expect that they would be.
The correct values for the latitude and longitude would have to be used and the gnomon would have to be checked and, if necessary, adjusted. After 97 years and presumably decades of use and/or neglect, it may well need adjusting.
Of course, the current value of the deviation of magnetic from true north would have to be found and the correction applied.
Astronomical yearbooks give the values for true solar noon (culmination of the sun), sunrise and sunset for a few days in every month. Otherwise, they can be calculated. I don't know the equations off-hand or I'd write them here. This is what I'm currently working on. They involve "The Equation of Time" and the "Julian Date" and aren't that difficult (it's just arithmetic).
Some brasso and scotchbrite and elbow grease should help fight that corrosion. Or if you have want you could could clean and polish the whole thing. But scrubbing off that writing from 1927 would be a shame
THAT’S RiiiiiiiGHT!!!!!
Okay?!
Given the age of that sundial, the correction for true north is no longer right. Get a current aviation sectional chart to find out the correct values for your location!
I discussed this towards the end
Phelps!
When's the multipication book lollll
I wawwwnn it
No link to the instructions. I have one of those and figured out how to use it. I think.
Sorry I forgot to paste in the link- it's in the description now.
archive.org/details/ansonia-sunwatch-instructions
I just read the instructions and the result can only be rough approximation. To get an accurate result, the true values of latitude and longitude must be used and an accurate time correction must be applied. I haven't checked this, but it appeared that the gnomon can be positioned continuously, i.e., not in steps. The instructions are very terse and don't go into the theory or how to get a more accurate reading.
In the northern hemisphere, the gnomon must point to the celestial north pole, where the star Polaris is located. If the sundial was at the north pole, this would be straight up. At Ansonia, Connecticut, 41°20′36″N 73°04′07″W, it would have to be pointed to the north (true north, i.e., magnetic north with the correction for the deviation from true north applied), and angled upward at an angle of 41°20′36″. This is the angle with respect to the plane tangent to the Earth at this location that corresponds with the direction toward the celestial north pole.
In the southern hemisphere, you would have to point the gnomon at the celestial south pole and at the equator, well, you're out of luck, at least as far as this method is concerned.
The correct longitude, in this case, 73°04′07″W, must be used because otherwise the time values will be off. The sun appears to move from east to west across the sky and culminates at true local solar noon. This is, in fact, the definition of true local solar noon: it's whenever the sun culminates. Since the earth is rotating, it culminates earlier the further east you go, so it will be noon earlier at 70° W and later at 80° W. That is, at a given moment, it's later in the east than in the west. Clearly, to get an accurate time value, the correct longitude must be used.
Of course, the surface the sundial is placed on must be level. Sundials can have oblique dials, but this affects the placement of the hour lines. And don't forget to wind it up!
Looool
Does anyone make a reproduction of this?
sundial laidnus
What a weird thing to yell at random people lol
True story but it didn't make it into the video: she ended off with "you think it's haunted?"
So you REALLY tried to use a magnetic compass sitting on a cast iron patio table grate? Amazing that you were within 10 minutes.
If you learn anything much about Navigation and Astronomy, you will realize that a sundial, properly constructed, along with accurate and precise data and correction calculations, can easily give accuracy to well under a minute. The only problem is that from the moment that someone asks you for the time, to the moment that you reply with the precisely and accurately corrected time indicated by the sundial, several minutes can pass, and so you will want a hack watch to record elapsed time, to quickly add to the found time, for the updated solution. The simple path to accuracy would be to pre-compute the time for a shadow position a few minutes into the future, and then the instant that the shadow hits the selected mark or position, you then have the time, right on the money.
No not really- it was just that one shot. I could tell the results were messed up so I did all my other ones elsewhere.
Just a gray void for a thumbnail? Yesterday it was the actual sundial... are you doing A/B Tests? The current thumbnail is NOT specially click-urgency-generating... 🤣
I'm using this new UA-cam feature: support.google.com/youtube/answer/13861714?hl=en_ID
Maybe some glitch on their end? Or your browser/app didn't load it right. I think all 3 thumbnails are working OK.
1:15 based
It may well be of interest to about 1% of those fascinated by old horology.
Beyond that it's useless.
How are you going to wear it?
What will you do when daylight saving comes in.
If you tried to explain all this today, you'll come across as a bore.
You don't wear it- you put it in your pocket. When daylight saving comes in, you add an extra hour. I tried to explain all this today- did I come across as a bore?
@ChrisStaecker you were most certainly not a bore
@@ChrisStaecker I'm subscribing because of this video, and this is the first time the algorithm has shown me your channel. Not boring haha
Sad story ending... 😢