*The Sundial*
By: GVI
31 August 2024
The reader of any Rubicon article deserves at least the suggestion of the motivation behind its creation. The honest truth is that this one is partly a challenge on my part.
A long time ago - practically upon my introduction to the Rubicon - I took upon myself the ambitious goal of writing a series of articles on practical astronomy and primitive mapping. I started several articles and but few are finished - one is merely awaiting photographs I've never got 'round to taking. I've alluded to practical astronomy in several essays "behind the Paywall Curtain," though an article on how to use The Almanac is available for everyone, as befits this useful little annual. But as yet I've done little for the public reader on actually using the sun, moon or stars themselves.
By this essay, I hope to begin to remediate my delinquency.
We will cover the following topics:
As it stands now, we have access to ridiculously accurate timekeeping via our computers and cell phones, which are tied in somehow (I couldn't tell you how - might as well be sorcery for all I know) to atomic clocks maintained and coordinated in several places around the world. Below this level we have our quartz and mechanical watches & clocks. But suppose we don't have access to any of these, and yet still have a legitimate need to know reasonably precise time? The sundial can provide this, but there's a knack to it.
Imagine moving you and those whom Fate has placed in your care from the danger of wherever-it-is-you-were to the relative safety of your pre-stocked retreat. Imagine also that you're like a lot of people I know, who have got out of the habit of wearing watches daily. Cell phones are out, internet's out, radios are either not receiving or the stations are not broadcasting, and your GPS is "bewitched." It doesn't matter how or why, but this image alludes to one such possibility:
This is far more frightening than any "sentient Skynet" apocalypse
(image credit: XKCD)
You get to your retreat, unlock the door and, Ganesha be praised, all is as you left it. Once the basics are seen to, you start rummaging around in the things you'd packed away, putting everything in order and getting the retreat "open for business" as it were. You open the shielded metal box where the site's electronics are kept and discover a pocket watch you got at a yard sale, and a quartz watch you purposely left with the stem out to preserve the battery. There's also a wall clock - mechanical or quartz, doesn't matter - among the packed-away things. The pocket watch is of course unwound but works fine when you wind it; and when you push in the stem of the quartz, you are pleased to find it works too, and the battery is in good condition - you also had the foresight to include a replacement battery or two. The key-wound or battery-powered wall clock is safe and undamaged, and you hang it up & get it going.
Now how the hell do you set them?
You can tell time to within about 20 minutes or so using any old sundial and no technique whatsoever - so long as it's oriented north-and-south - sorta - you're good to go. With a good sundial and relatively easy technique, you can get time down to the nearest few minutes or less, which is usually sufficient for setting our watches and clocks. Getting time any more accurate than this requires techniques and instruments which are not only beyond the scope of this essay, they are also of very limited practical utility.
The sundial at the entrance to Chicago's Adler Planetarium is accurate to under a minute, but reproducing it at this size is beyond the means of most of us.
Backing it up a bit, this article will tell you what makes for a good practical sundial, and how to use it to determine "mean civil noon" (we'll explain this in a bit) to within less than five minutes.
ONE IMPORTANT NOTE:
Prayers of the Abrahamic religions end in "Amen;" Buddhist prayers end in "Sādhu," Hindu prayers end in "Swaha" and scientific research papers end in "Further Research Is Needed." They all mean the same thing. Likewise, an essay on practical astronomy is incomplete without a word about "apparent motion."
We all know the Earth travels about the Sun and not the other way 'round; however, in practical astronomy, the Sun is treated as though it travels across the Earth's sky for the following reasons:
It is a convention in writing, done mostly for brevity's sake, and everyone understands the proper relationship between the Earth and the Sun without the annoying nuisance of having it spelled out Every. Blooming. Time.
Amen - So Mote It Be.
If you can believe it, reputable firms were making high-quality sundials for explorers and the military as late as the 1930s. Stands to reason once you think about it a bit. Watches from the 1930s and before are all mechanical and need to be wound every day, preferably at the same time every day. A high-quality mechanical watch will have a consistent error (gains or loses so many minutes per day in a predictable manner), but an average- or low-quality mechanical will have a random error (gains or loses depending on how it's feeling that day - kind of like us). Either way, watch correction for things like surveying or celestial navigation was a fact of life as late as the 80s, which I know because accounting for it was an unavoidable step in calculating astronomic observations in Field Artillery Surveying, which was my job in the Army. And while the expedition (or expeditionary force) may have had a good radio set with it, it was not always possible to receive the signal from a station broadcasting the time. Before reliable shortwave broadcasts and convenient receivers, having an independent means of setting one's watch was even more critical. The link to the "Compass Museum" page on sundials at the end of this article displays a vast array of different types of sundials, and nearly all of them were serious instruments meant for "paying work" - they were not toys or curiosities. The permanent exhibition of "primitive astronomy" at the Adler Planetarium has many that are true works of art and ingenuity, accurate to within the limits of construction at the time they were made.
We are farther in technological advancement from the sundial's relevance than we are in time; and as any good Rubie knows, we can go back to that level of advancement at any moment.
All sundials work on the same principle. The shadow of an indicator (called a "gnomon") is cast by the sun onto the "dial" which is marked so as to tell time. All sundials must be oriented directly north-and-south (TRUE north-and-south, not "magnetic" or "grid") for them to be at all accurate. Their precision (not the same thing as accuracy) is a function of their size and the materials used in their construction - a larger sundial can have finer graduations, and a thinner or sharper-edged gnomon will display its time more clearly. Some types of sundials use fine wire or silk thread for their gnomons.
A reproduction of a very high-quality portable "equinoctial" sundial that accounts for latitude, direction and date, which can be leveled.
This example displays pretty much everything desirable in a sundial from which accurate results are expected.
Many sundials were painted or carved onto the sides of public buildings, the gnomon being either a metal rod or a projection of the stonework. Some of them are quite beautiful. If your property has a building (or even a section of fence) that gets sunlight all day and faces exactly south, this is an option for a very precise sundial.
The motto under the window on the right is often found on public sundials. "Horas non numero, nisi serenas" is a play on words that can be read two ways.
It either reads "I only tell time when the sun is shining" or "I only count sunny (i.e., happy) hours."
In the realm of "What can I buy right this second?" we have this:
Knock-off copies made by illiterate, barefoot peasants in a Bombay sweatshop, but reasonably well-made and of sound design.
This is an original instrument, ca.1919. It has two non-adjustable spirit levels which the knock-offs lack, but you can get cheap spirit levels at any Big-Box hardware store.
This "equatorial sundial" goes for well under $30.00 on Amazon. I got the brass ones above some time ago. The shiny one, which was a gift to my daughter, cost a measly $17.00 and, with the addition of a Big-Box fish-eye level, is entirely adequate. This is an absolute pittance, especially when you consider that the original was made by Francis Barker & Son, a London firm that did NOT make cheap instruments. I have a scanned example of a British catalogue printed in 1881 that lists the price for this instrument as 3 pounds, 8 shillings and sixpence. According to the Bank of England, this sum, accounting for 140 years of inflation, amounts to 426.48 Pounds-Sterling today, or $575.50 in United States dollars. For what it is, what it cost and whence its pedigree comes, my Indian knock-off is quite reasonably well made and worth the price.
As portable sundials go, I'm satisfied with the ones I bought. They are clearly less well-made than the original - the differences such as the presence of the spirit levels, the design of the gnomon and the scale on the underside of the disk - show an attention to detail absent on the inexpensive reproduction. For all that, the repro is fit-for-purpose. The compass needle is balanced for the middle Northern latitudes (you won't have an annoying dip problem), the latitude bar is reasonably correct, the needle-lift lever works as it should and the device can be precisely leveled. It's more delicate than the original - the sundial disk, for example, is made from a relatively thin piece of sheet brass, where the original is cast. The needle is not damped - it will take a while to settle down.
The bubble will move whichever way your left thumb is moving
This sundial can be very accurately leveled if placed on a firm surface. Raise the latitude bar and disk and orient the sundial to TRUE NORTH. With your left hand, use the three screws to level the sundial - the bubble will travel in the direction your thumb is going. If you're moving the screw counter-clockwise, your thumb will be moving toward the right and the bubble will travel toward the right. Move a screw clockwise and your thumb (again, with your left hand) will be moving left, and the bubble will travel to the left. Surveyors have a way to level their instruments using two screws at a time, but learning this trick isn't necessary - just center the fisheye level using one screw at a time with your left hand.
When orienting the compass, remember that the needle needs to account for your local declination. For example, at the time of writing [NB this essay was updated August 2024], my local declination is 4 degrees, 32 minutes West, changing 3 minutes per year. This means my needle should be pointing to around 356-355 degrees (360-4.5 = 355.5). One thing I noticed about this sort of sundial is that when you get it new, its dial is quite polished and shiny - it's tricky to find the gnomon's shadow on it. The tarnished example shows the gnomon's shadow better, and will be used in the demonstration. Wiping unvarnished (bare) brass with a vinegar-soaked paper towel will add an acceptable-but-harmless patina that can always be polished out.
Lawn-ornament sundials are fine things to have, provided they are permanently and carefully installed (pointing to True North and not magnetic north), appropriate for your latitude (this is a bigger deal the farther south you go) and so situated as to be unobstructed by the shadows of trees or buildings. I suspect these are available practically anywhere you can find lawn ornaments, and I know Amazon sells a variety of them. Chez GVI has no place that fits the above criteria - it's a small city lot that's surrounded by tall Norway maples - therefore we will not discuss them further, though they're an option if home or retreat can support them. Of course, you can't stick these in a pack, on a pack mule or in a vehicle, but we've already covered smaller instruments.
At the "Ridiculous Meets the Sublime" end, I also happen to own a bandana with a "sun compass" printed on it. It's made by the company at this website. The "sun compass" bandana "works," kinda, provided you know the time; because of this, it also has the curious capability of working backwards as a sundial if you happen to have a compass. Time, location and direction are all linked together.
More a curiosity than a practical artifact.
It won't tell time as accurately as we're discussing, but technically it is a sundial.
It doesn't really matter what kind of sundial you use, provided
A sundial of course measures time relative to the movement of the sun. But the Earth does not orbit the sun in a perfect circle with the Sun at its center, nor is Earth's axis perpendicular to its orbit. For these reasons, the duration of daylight and the length of an hour as measured by the sun varies from day-to-day and place-to-place - sometimes imperceptibly, sometimes by quite a bit. We know this by the fact that it gets dark early in winter and late in summer, but we seldom give the issue much more attention. And why should we? Accurate timekeeping is presently Someone Else's Problem (e.g., the sorcerer with his atomic clock), and the real difference between "mean civil time" and "solar time" is something we ordinarily take no notice of.
An example of the "analemma," the figure produced when you take a photo of the sun from the same place at the exact same time over the course of a year. This one is over the temple of Apollo at Corinth in Southern Greece.
Before we go further, let's get caught up on a few definitions:
There's another "time" called "sidereal time" which refers to how the stars in the night sky appear to rotate around the earth, and it's different both from solar and civil time. We'll deal with it in a future article, but it's not important when using a sundial. I bring it up here only to note that if you see the word elsewhere, understand it relates to the night sky and not the sun.
There are several ways to represent the difference between the earth's orbit around the sun and the effect this has on the sun's place in the sky at, for example, noon "mean civil time." You can get the hint of it by spending a while studying the following graphical representation:
The circle represents "mean civil time" and "local time" whose hours never "expand" or "contract." The irregular red line represents how "fast" or "slow" the sun is with respect to mean civil or local time. Except for four days of the year, the sun either arrives on the observer's "meridian" (straight South) before "noon, mean civil/local time" has occurred, or after.
If you're the type of person who "thinks graphically," this image would be sufficient to get started. But while I find that it does a good job of illustrating the concept, I don't think it's the easiest way to make use of the phenomenon. It's illustrative, but it's not practical. Until I finish calculating an Equation-of-Time booklet, to be included as a companion to this article, the best place to find the difference between "civil time" and "solar time" is an Almanac.
A word about "Unequal Hours"
The reader ought to have noted by now that while I've talked about the sundial as being useful for setting time on a mechanical or quartz watch, I've said nothing about actually telling time throughout the day with it. This is because doing so is more cumbersome than just a correction for local noon - so cumbersome, in fact, that I consider it not worth the effort. This next sub-section will explain why.
Refer back to the photo of the "analemma" above. Again, it's what you get when you take a few dozen pictures of the sun at the exact same time and location throughout the year, and put all the images together. The width of the "figure-8" it makes represents the correction from "local solar noon" to "civil time," and is related directly to the eccentricity of the earth's orbit around the sun - refer to the diagram above. But note also that the sun moves up and down in the sky throughout the year. This is due to the tilt of the earth's axis, and explains why the days are so much longer during the summer months than in the winter - the sun is up for a longer time in summer than winter.
But an ordinary sundial only records time as the 14 "solar hours" between 5:00am and 7:00pm - am meaning "ante (before) meridiem/meridian" and pm meaning "post (after) meridian." A "solar hour" according to a sundial is longer than a "civil hour" in the summer and shorter than a "civil hour" in the winter, and only approximately equal to a "civil hour" at the equinoxes. Some sundials allow for the difference in "solar hours" but portable-and-affordable ones don't.
An exhaustive explanation of a sundial's capabilities, limitations and the procedures needed to bring out their fullest potential - that of telling time throughout the day and converting solar time to civil time - is well beyond the scope of this essay, which is already long enough to test the reader's patience. In a preparedness context, all we really need a sundial for is to set our watches; and to do this, it is only necessary to read it at "local solar noon" - that is, when the sun is exactly at the observer's meridian - and to understand how this phenomenon relates to "mean civil time" which is the time our watches and clocks tell us. A sundial can do more than merely this, but for the prepper, "the juice isn't worth the squeeze."
In order to convert sun time to watch time, we need a few things:
NB: Latitude has more of an impact on sunrise/sunset than it does on "local noon," so it need not be taken into account.
Sundial, properly oriented and leveled
We've already discussed the sundial itself. We need to make sure it's oriented to True North, not magnetic North. If your sundial comes with a compass, orient it to take your local declination into account (you can look elsewhere to figure out how to find your local declination or you can just use This Government Website That Finds It For You and write it down (along with the annual rate-of-change) somewhere handy. If you don't have a compass on your sundial, either use your own to orient it correctly or point it to Polaris, the North Star, on a clear night. Make sure it's level.
The North Star is not that bright, but it's not that hard to find either
Longitude
The next thing we need is our longitude to within 15 arc-minutes. We need this only if we're using one of the commercially published Almanacs and not "Astronomical Phenomena" or the Nautical Almanac, and we need it in order to correct the "local noon" the commercial Almanacs publish to our location.
You are here
It's likely, if you're reading this, that you're also here (ignore the pin over Alberta)
The time zones we all live in are roughly 15 degrees in width. This is because the sun appears to go around the earth every 24 hours. The Earth is spherical (Flat Earthers can go kick rocks), so it has 360 degrees of longitude, numbered to 180 east or west of the Prime Meridian at Greenwich. Dividing these 360 degrees by the 24 hours the sun takes to go through all of them, we see that the sun crosses over 15 degrees' worth of the Earth's surface in one hour. Dividing further, we discover that the sun takes 4 minutes to traverse each individual degree; dividing yet again, we see that the sun crosses 15 arc-minutes of the earth's surface in one minute of clock time. Since we'd be doing VERY well to read any sundial to the nearest minute, it's unnecessary to go any further.
If you're wondering at this point how on Earth you're going to know your longitude to the nearest 15 arc-minutes, it's not as hard as you think. For our present purposes, "the nearest 15 arc-minutes" is so close to saying "the nearest 15 miles" that the difference is negligible. An arc-minute is more-or-less one nautical mile at the equator, and a nautical mile is a bit longer than a statute mile. Since most of my readers are in the middle-latitudes, "an-arc-minute-is-a-mile" is close enough.
There are several ways to get your longitude. If you have a USGS 7.5-minute quad map for the area you're in (or indeed any map with latitude-and-longitude at the margins), you can find it quite precisely by scaling. You could get your longitude from Google Earth; but if you need a sundial to set your watch, you're unlikely to have access to Google Earth information unless you wrote the results down beforehand (in the same place you wrote your magnetic declination). However you get your longitude, figure out which multiple of 15 arc-minutes (0, 15, 30 or 45) you're closest to, and use THAT longitude for your calculations.
To use my own location as an example: Chez GVI is at 87-degrees, 03-minutes West Longitude. If I were in Gary, whose longitude is 87 degrees 20 minutes west, I'd "round down" to 87-degrees, 15-minutes West, because 20 is closer to 15 than it is to 30.
We'll work it out with all the corrections in a bit.
Date
I'm not entirely sure how it is you or those around you wouldn't know the date. But you need this for the "Equation of Time" tables that follow.
Equation of Time
The Equation of Time sounds like some ominous, mystic secret from a fantasy movie where everyone's chasing after it like it's some sort of occult MacGuffin. It sounds like "The Riddle of Steel."
"What is time, boy, compared to the clock that tells it?"
James Earl Jones and his heavy-metal friends aren't going to hunt you down for knowing what the Equation of Time is. It is simply the difference, one way or another, between Solar Time and Mean Civil Time like we discussed before. There is a mathematical way of sorting it out, but it's so complicated that it's far better to just look it up rather than try to puzzle it out with a paper and pencil.
If you have a copy of Astronomical Phenomena, the Nautical Almanac, the Old Farmer's Almanac or the Farmer's Almanac for your year (discussed in the Almanac article), you determine this difference in one of several ways, depending on which one you find easiest to use. If you use one of the government publications ("Astronomical Phenomena" or the Nautical Almanac), you simply take the number they give you and add or subtract it from "local noon" - no further correction is necessary. Harris Farmer's Almanac does not have this information, and Hagerstown (which I mention in the appendix of the Almanac article) doesn't have it in a conveniently useful form.
I had considered preparing an "Equation of Time" table for this article, set in printable booklet form, that would work for as long as the grandkids of anyone reading this could reasonably expect to live. I may yet do this and include it in the future; but since getting this article out in a timely manner is more important than
a) holding its publication up while I compile a huge table or
b) staying up way too late doing the calculations on a deadline,
I'm afraid it will have to wait.
Stay tuned.
Since the corrections in the Equation of Time repeat themselves every four years (coinciding with Leap Years), it makes sense to hang on to Almanacs for four years from their date of issue. For example, the Equation of Time in an Almanac current for the year 2022 (the year this article was originally written) will be good for the years 2026, 2030, 2034, 2038 and so on. The values in the tables change but slightly, one four-year period to the next - on the order of tenths of a second every four years. Since we're concerned with whole minutes, this small change is negligible; four years' worth of Equation of Time data in Almanacs can be used without alteration at least until the United States' Tercentennial, if you can believe it.
As I said, how you determine the "Equation of Time" depends on which book you're using. If you're using a "government-issue" almanac, you simply take the number it reports for the day and add or subtract it (as the case may be) from "local noon," and this is the time when the sun will cross your meridian. It's as simple as that.
If you're using a commercially published almanac, each of the ones I recommend has a different method. This relates to the commercial Almanacs in the following way:
Again, if I'm using the "Astronomical Phenomena" or the Nautical Almanac, I don't have to do a thing - I can use their "Equation of Time" figures straight out of the book, adding or subtracting from "Local Noon" as the case may be.
Some setup needs to happen before "local noon," that is, when the sun is directly south of you and near the 12 on your sundial:
Accounting for Daylight Saving Time means "local noon" is going to happen nearer to 1:00pm Mean Civil Time. In other words, if you were doing this on June 13th of this year in Denver (Latitude 105-degrees West), your watch must be set to exactly 1:00pm Mountain Daylight Time in order to coordinate with Local Solar Noon.
Next, carefully watch the shadow on the sundial for when it just touches the mark for noon. If you have a quartz watch, push the crown in to start the watch - you're done! If you have a wound-down mechanical watch, give it a shake to start it ticking, then start winding it. Once it's running, set the time, WITH the corrections from the Equation of time and longitude, on your watch and finish winding it. If you have other watches or clocks with you, set them as close as possible off of this "standard" watch.
A quartz watch with a good battery will not need to be checked any further. A good mechanical watch that you wind the same time every day (right before bed is a good time) only needs to be checked every two weeks or so, and only the Equation of Time needs to be accounted for. A mid- or low-quality mechanical (like an old Timex, Benrus, etc.) ought to be checked weekly.
Everything I need in order to set my watch from a sundial. The standard is the government's official timekeeping website (see link below).
Here's how the example works at Chez GVI for today, which is 16 October 2022:
"Local Noon" on my sundial
This is how far I was off, comparing the watch to the government's official time - a minute or so, give-or-take.
Like many things, this takes more time to describe than to actually do, and sounds a lot more difficult than it really is. With practice, sundial use becomes nearly intuitive. It took me a total of ten minutes to perform the entire procedure, starting about 12:04 CDT.
The previous demonstration was done in October of 2022. What follows was performed on 3 August 2024. Its purpose was to show that a compass can be used stand-alone as a sundial, similar to the manner I described above. It differs from the previous demonstration in that we now know we can set a watch to a sundial - this was done simply to prove that the same phenomenon applies equally well to a good compass, with some small adaptations.
Everyone kind of ought to know this already. I have compasses in my own collection that were specifically designed to "take the solar meridian."
"SHUT UP! I CAN QUIT ANY TIME I WANT TO!"
The real purpose of this demonstration was to show that a quality compass will represent the "time/direction/location" relationship just as well as a dedicated sundial. It's essentially a repeat of what I did a couple years ago, but with a different instrument and a few additional considerations.
The first consideration is what compass to use. I used a Cammenga Model 27 - the version of the U.S. Army's M1950 Lensatic Compass that doesn't have tritium for self-illumination at night.
Let's Talk About This...
What you see here is what you need in order to do everything we did above with a sundial, in combination with knowing your own longitude and date. Let's talk about each thing:
Compass:
The choice of compass was deliberate. The Rubicon adopts the M1950 as the standard against which others are compared. Other compasses may be "better" for a given purpose, but they're all compared to the M1950; if you could only have one, you could do far worse than spend the money to get the government-issued one. It's rugged, reliable, truly "global," and in all respects satisfactory for the average user. And it's nearly ideal for the task it was put to here.
Many different compasses will work for what we're about to do, but some are better than others. Those with a fine wire for sighting like the M1950 are best. The one on the tripod, a few photos above, was made with this type of operation expressly in mind, at a time (1820s) when knowing how to do this was much more important. Those with a finely-marked line on a glass or acrylic face will serve as well.
Some rarer compasses, such as the European "Bezard," will not work if the sun is too high in the sky - sighting with this compass is through two slits in the lid which limits its utility in the lower latitudes and in summer. Some, like the Silva and Suunto "baseplate" compasses, simply won't work for this application.
Romanian compass similar to Bezard: marginal - note the size of the illuminated area in the shadow.
If the sun were higher, that lit area would be smaller yet or nonexistent.
Baseplate compasses: good instruments, but not for this application.
The one on the right will work, but be hard to see
The one on the left is wholly unsuitable
Quartz Timepiece:
You don't need a pocket watch like this one. A wristwatch or a small, portable clock will do provided it's accessible, and those with a quartz (battery-powered) movement are best.
I come from a family of watchmakers, and my preferred watches for daily wear are all mechanical (wind-up). Setting this preference aside, I wear a quartz-movement watch when I'm in the field or when I need unfailingly precise time. Any quartz watch will do - their movements are all the same and they're all just as precise - around a single second of variation per month.
I selected this watch because a) it has a quartz movement and b) it photographs well. Use what you have.
Almanac/Astronomical PhenomenaThe "Astronomical Phenomena" booklet used to be faithfully published annually, two years in advance, but it's become harder and harder to get the next year's number - certainly more difficult than copies of the Nautical Almanac, which I've now had to begin buying. I've written the Government Printing Office concerning "Astronomical Phenomena" asking them if publication has ceased, and received the following in reply: "No, it's just delayed by the publisher. The last issue we had was the 2024 ed. We are waiting on the 2025 ed., we just don't have an exact date for delivery at this time." I'll keep my opinion to myself - this article is long enough already.
The Old Farmer's Almanac or the Farmer's Almanac (discussed in the Almanac article above) both have the same exact information - so long as they're available, you don't need the government publications, though these are of course the "gold standard" in accurate information.
The several resources put their information in various formats:
"Astronomical Phenomenon" - Accurate to nearest second.
Tells you how many minutes/seconds to add or subtract in order to know when "local solar noon" happens.
"Old Farmer's Almanac" - Accurate to nearest minute.
Tells you the same thing but for Boston - follow the directions on the "How to Use" page to get the proper correction
"Farmer's Almanac" - Theoretically accurate to nearest second, real accuracy to nearest minute
Tells the same thing for their "standard meridians" - you must know your longitude (see Almanac article above) and must be interpolated for greatest accuracy
I haven't taken a photograph of the Nautical Almanac because I never discussed it in detail, but the full-size annual has the same data as the "Astronomical Phenomenon" booklet. It's in the lower right corner of the right-hand "Daily Page" for your date.
Setting up:
Setup was similar to the sundial operation. At least ten minutes prior to "local solar noon," determine the difference between "local solar noon" and "local civil noon" like in the previous section, and set this difference - one way or the other - on your timepiece, making sure it's not running. I left mine running after having set it precisely to Greenwich Mean Time, in order to demonstrate that the operation will work; but if you're setting your watch or clock by the sun, you'll be waiting for "local solar noon" to start it running. Set your compass up on a level surface and, like in the sundial operation, orient it so the compass body is aligned to True North - not Magnetic North!
Once this is done, watch the hairline shadow of the sight wire carefully. You'll see it creep from right-to-left toward the "lubber line" on the body of the compass - NOT the north-south line of the compass card or needle!
Sight wire shadow to right of "lubber line" on compass
Once it hits this "lubber line," start your watch.
Sight wire shadow and "lubber line" are superimposed
It won't take long - less than a minute - for the sight wire shadow to pass to the left of the "lubber line." Accounting for the unavoidable errors of alignment and leveling, as well as the limitations of the instrument and method, our timepiece will be within a couple minutes of "mean civil time."
It took less than a minute for the shadow to move from one side of the "lubber line" to the other
The reader may well wonder why I bothered to write the first section at all when it's possible to perform this operation with a good compass. There are a few compelling reasons. First, at the time of writing, the sundial I described above costs around $20.00 on Amazon, and a compass I really like goes for about $30.00 or so. The Cammenga Model 27 we used in our demonstration sells for $70.00 and it doesn't do everything the cheaper compass in the link can do. The second reason is that the sundial I recommended can be leveled very easily, whereas this is somewhat more difficult with the Lensatic compass and the cheaper one. Neither has leveling screws, and just judging by the tilt of the compass card is bad practice, since the compass card will naturally "dip" (because of magnetism and latitude) when properly leveled. The cheaper compass has a fish-eye level but no good way to level it without a tripod. The use of the compass for this application should therefore be considered "next-tier-down" from a dedicated sundial.
Ten years ago, I wrote an article for the Rubicon about timekeeping and watches/clocks generally. In it, I referred to the sundial as "Ancient, archaic or useless." In my defense, it was a long time ago, I wrote it in innocent ignorance and really, the sundial has only very limited utility to the average prepper. To a degree, this still holds true; sundials and their use reflect an age where the agrarian use of time (related to the amount of usable light in a day for farming) was more important than industrial uses (for train timetables, navigation and the like). Once the needs of industry supplanted the needs of farming in relative importance, solar time took a backseat to civil time, such that nowadays it's not even on the same bus! However, the interest in primitive astronomy my irregular series seems to have generated reminds me not to make such sweeping generalities in the future.
Web Links
https://www.compassmuseum.com/sundials/sundials.htm
The Compass Museum's section on sundials. This site is a delightful time-waster, as it has more information on compasses, sundials and other such instruments than anyone could ever want to know.
https://www.time.gov/
United States official time, from the National Institute of Standards and Technology. A great place to check your work before you need it (this is how I set the second "check" watch you see in the photos)
https://www.sundials.co.za/THE%20SUNDIAL%20GOES%20TO%20WAR%20web.pdf
"The Sundial Goes To War"
This link downloads an article in pdf format, which discusses the use of the sundial and related "sun compasses" in World War II.
www.alpharubicon.com
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