Equatorial Equatorial Sundial

Human Sundial

Human Sundial

Original Image

At the equator, the line of stones would run directly East / West and you would be unable to adjust for the person’s height by having them step along the path. So making this kind of sundial at the equator has a unique set of problems. However, you could have them stand in the middle of a wheel, arms extended N / S, and make an equatorial sundial… A Human Equatorial Equatorial Sundial ;-)

I was contemplating the steps needed to make a Henge. Something I do from time to time as I’d like to have a Henge of my own someday… and (sung to the tune of “Everybody ought to have a slave” from A Funny Thing Happened On The Way To The Forum ):

“Everybody ought to have a Henge. Everybody ought to have a work-ing dial!”…

I’d started listing all the uses, how to get them from a Henge, and working out the most likely steps and stages along the way. One of the uses is as a calendar. Another is as a time standard (we’ve looked at that briefly in earlier postings). That got me thinking about alignments and clocks. Was there a ‘clock’ function at Stonehenge? I’d proposed using a star transit timing as the first step of making a length standard and as part of laying out a Henge; but might there be a more formal ‘clock’?

At which time I remembered the thousand and one ways to make a sundial and realized that just about any vertical pole could have been a sundial (and horizontal poles too…).

Oh, and I’ve been thinking about making a Henge at the North Pole and at The Equator and what would that do to various aspects. Basically, how much does a Henge change as you move from Equator to Pole. That got me thinking about a sundial at the Equator.

OK your typical sundial has a center line that points at the pole star. This aligns it with the axis of rotation of the earth and you get a nice shadow line for marking time. (There’s a lot more than that that goes into sundials and some are truly magnificent with built in allowance for all sorts of things, some seasonal and some longer… but that’s out of this scope.) But at the equator, that line would be perpendicular to the earths surface. If placed on the top of a pole, it would make a T shape (or look like a crucifix if placed part way up the pole) with the top aligned North South.

At that point, you would just mark the ground with 5 divisions each side on an east west line and have your sun dial (each being 15 degrees of arc about the top of the T. You don’t need a 6 am or 6 pm line as they are an infinite distance away floating over the horizon ;-)

As the seasons change, the sun is straight overhead during the equinox and slightly north or south during the solstices. So you could mark lines (about 3.9 degrees each N / S or 23.4 / 6 ~= 3.9 ) and put month names next to them. As the months progress, the shadow would move north or south and align with a month marker. For each month, you mark the arc the shadow traces on the ground and then mark the hours on it. Now you have a sundial that tells you both month and time. (If you wanted to get really fancy and were precise enough you could even mark weeks or days, but that precision is hard to come by in outdoor constructions).

This device is basically an “Equatorial” sundial, but built at the equator (thus the Equatorial Equatorial posting name ;-) as that puts the ‘axis’ parallel with the earth axis as the cross beam of the T or crucifix. For an in depth look at equatorial sundials, this page has directions on how to make one. They often take the form of a large wheel with a pole through the axle pointed at the pole star and markings on the wheel for time. Like this one:

Equatorial Sundial in Beijing

Equatorial Sundial in Beijing

Original Image

At the equator, the ‘axel rod’ would be parallel to the earth surface and pointing north south. You could use a wheel for the markings, or just have a pole hold up the rod and mark the ground as described above.

But at that point, you don’t really need the cross beam and can simply leave it out. The end of the vertical pole alone being enough to mark month and hour… At that point, you have become a different specific kind of sundial, the vertical pole analemmatic sundial rather like the one here that I usually think of as the antithesis of the equatorial sundial. Odd, that at the equator one transitions into the other…

Not surprisingly, there is a North American Sundial Society for folks really into this kind of thing and all the ways to tell time by sundials. (There are also various ways to do the same at night, but that’s for another posting…)


and a wiki on sundials:


So at this point I’ve come to realize that in my quest for a Henge at the equator, the very first step is to put in a flag pole or crucifix and some paving stones or selected flowers arround it. “Half past the petunias on the granite month line” has a certain charm to it ;-)

Then I could properly schedule all the work on the Henge construction project and know when it was time to break for lunch. It will also give you the equinox and solstice days (as maximum and minimum N/S excursions of the shadow) for your initial star sightings for Henge alignment.

With proper placement, this pole can also serve as either the first ‘central sighting pole’ or the ‘solstice sighting pole’ of the first step of Henge layout. Either at the exact center of your future Henge, or on the perimeter of the outer ring at the end of the Solstice Line from the center toward the horizon on the day of the Summer Solstice.

So where my ‘first step’ had been “get two poles and some rope”, instead it’s become “get two poles and some rope, and some stones. Make one pole into a sundial at the center of the future Henge.”

Odd that the first step of creating a Henge ends up at time keeping, project management and the metrology to do it. Or maybe not so odd. It would be a big project.

In an earlier posting on the English Foot we saw one of the ‘next first steps’ is to mark a 15 degree angle on a circle. I also find it interesting that the Equatorial Sundial uses 15 degree arcs for each hour. In the case of the sundial, we align the plane of the circle to the plain of the ecliptic and use it to mark hours. In the case of the Henge, we align the plane of the circle to the earth, then mark the transit of a star from pole to pole and use that to make a time standard, and from it a length standard (the Rod and the Megalithic Yard).

This, now, makes me wonder if perhaps the first step ought to be making an equatorial sundial and using it to make a standard of time, and from that a standard of length. Basically, the length standard can be made more precise with a larger “star dial”, but does not actually need one and could be made with a sundial instead. Each is timing the rotation of the earth. Each is then calibrating a pendulum from that to make the length standard.

So we could use a transit of the sun, moon, or stars, as we like it, and as we need more or less precision. I’m going to have to think a bit about exactly when is the best time of the year to use a sundial to make a Rod unit of length. Or perhaps look at the rod and figure out what time the ancients selected. Basically, their length standard ought to tell us when and what time standard was used to create it within the known margin of error. Did they know the date with the most precise hour? And how much does it vary from place to place and season to season? How much did they know about The Equation Of Time? And is that reflected in their unit of length? I note that the equation of time has a ‘near zero’ at June 13th, and that’s rather close to the Summer Solstice in the northern hemisphere…

Subscribe to feed

About these ads

About E.M.Smith

A technical managerial sort interested in things from Stonehenge to computer science. My present "hot buttons' are the mythology of Climate Change and ancient metrology; but things change...
This entry was posted in Science Bits, Stonehenge and tagged , , , . Bookmark the permalink.

11 Responses to Equatorial Equatorial Sundial

  1. a jones says:

    Well I don’t know about a henge of one’s own although a great schoolboy friend’s family owned the land, and thus the Rollright stones, which is a sort of henge on the Oxon/Wilts border and made a handy little income charging people to see it: and for all I know still do.

    Of course if you should visit the Isle of Man in Castletown you will find a Moondial still working perfectly well after all these years. Although you have to wait for the streetlights to turn off before you can see the full effect. And then only on cloudless nights when the moon is near full.

    Kindest Regards

  2. H.R says:

    “Everybody ought to have a Henge.”

    I have already built a stone “Gateway to Nowhere,” laid about 4 tons of flat limestone boulders for a koi pond (50-300 lbs each) and set about 18 tons of the flat limestone (200-1,200 lbs each) landscaping the front yard. Don’t give my wife any other ideas. I’m begging you! My back can’t take it any more.

    BTW, winter sledging over frozen ground for very heavy stuff works great. You’d be amazed at what can be moved. That’s how it was done in days of yore.

  3. pyromancer76 says:

    Perhaps of interest. At PhysOrg there is a story about a new henge discovery. It’s along the lines of “everybody ought to have a henge”. Perhaps they did!

    The new “henge-like” Late Neolithic monument is believed to be contemporaneous to Stonehenge and appears to be on the same orientation as the World Heritage Site monument. It comprises a segmented ditch with opposed north-east/south-west entrances that are associated with internal pits that are up to one metre in diameter and could have held a free-standing, timber structure.

  4. E.M.Smith says:

    There are giant Henges scattered all over Europe. I expect there were lots of “baby henges” with one in every village of importance too… but nobody thinks twice about a circle of fence post holes… (We probably would not have known about Woodhenge but for it being so near to Stonehenge that folks figured it out before it all got ploughed into wheat…)


    Found due to an arial photograph…

    So I’m pretty sure that a load of ancient farmers had their own solstice aligned poles and their own equinox markers and maybe even their own lunar month counters (30 holes with a movable stone or pole; though as easily done with a wooden plank and a pebble…) and that we’d find none of it in the landscape today and have little chance of the typical archaologist recognizing it if they did see it.

    I presume the story you are talking about is this one:


    I’ll take a look…

  5. E.M.Smith says:

    OK, I found a bunch of articles there about a Blue Henge and some other wooden ones. All of them riddled with the Ritual Religion junk.

    FWIW, my “interpretation’ is more direct. You have the embankments and the cleared “Cursus” and all for the simple reason that you need an absolutely level and clear horizon line for the most precise results. NOT religous procession nor ‘sacred dirt’ nor … Just a clear and level horizon.

    The reason there are so many other minor henges about, IMHO, is that Stonehenge was The Big Boy and all the other Henge Wannabe guys came here for Henge School. So we find Woodhenge and Blue Henge and lord knows what other henges as the undergrads study on one, the graduate students move up a notch, and the Ph.D. Henge guys do new obervational work on The Big Instrument. Exactly as we find today at observatories.

    Oh, and the burrials? So you have a giant society wide party every year at Yule with drinking and gluttony and you don’t think some percentage of folks are going to die in accidents, illness or fights? Yeah, 3000 BC you just stuck them in a hole “over to the side” and went back to work / party time. No Big.

    What is missing in modern archeology is a sense of the mundane…

  6. kuhnkat says:

    E.M. Smith,

    while you were researching did you run across the info on the Celtic Cross and other ancient tools as both a way to tell time and a navigation tool using both longitude and latitude??

    The prescession of the earth that can be measured with your henge is the basis of making it work apparently!!

    Definitely agree that much of the interpretation of what is found is colored by the bias of what the finders are expecting!!

  7. P.G. Sharrow says:

    A thought has me wondering, Would a small henge be useful for land navigation? All over the world on hills and ridges there have been found small rings of spaced stones. If you have been wandering, exploring, hunting in a new area, could you use a small temporary henge or stone ring to lay out the fastest way home? or at least exactly where you are. The need to navigate across vast distances on land and then on sea has been a part of the human experience for a very long time. Keeping track of the days, months and seasons is not the only need of earlier populations. Accurate maps and memories were vital to survival of hunter – gathers. pg

  8. P.G. Sharrow says:

    The Idea of a sundial brought a smile. The walkway and door to my cabin faces directly south so I know the time when I walk in from the gardens. :-) By my shadow on the walkway and door. pg

  9. E.M.Smith says:

    @kuhnkat: I’ve read a discription of it once. It’s on my “someday” list to get/make one and learn to use it properly. Only a vague understanding right now. Sort of a portable astrolabe and suncompass thing…


    Yes, they would, though other devices might be easier. First off, when things are cloudy it’s very hard to get a solar, stellar, or lunar “fix” on where you are. Leave a small henge behind and you’ve got an instant compass. Have a note that “home” is 10 degrees NNW of the solstice line, you can then sight the terrain and head out toward the next landmark. So “inbound” you stop on hills every so often, set up a crude henge (based on as close a guess of the alignments as you can make given the knowledge of the date) on whatever clear day you have. Upon the return trip, it’s now a guidepost for “dead reconning” … sort of a GPS spot to orient your map…

    It avoids the “we go to the top of that hill next” then a long wander through a valley floor and up to the top and it’s a cloud deck. Camp for a week (or a month or..) or just look at the henge and take a bearing.

    If you mark N, S, Solstice, Equinox, and a couple of star alignments (one for each season?) then any latitude and longitude ought to be ‘recoverable’ from the shape of the henge and compass points clearly are. Clouds or no clouds.

    Oddly, if you get a modern aviation map, you find these same circles all over it. But they are radio beacon VORTAC stations…


    All over the world, airliners converge on them as ‘waypoints’ on the ‘highways in the sky’. So folks on foot would just be doing the same thing and doing it as “this mountain’ to ‘that mountain’ instead of ‘this radio compass rose’ to ‘that radio compass rose’…

    I’m HERE. Sight to mountain W 280 degrees and about 10 miles. Set mini-henge in place with solstice line, N/S, and pointer at 10 Mile Mountain. Set out over the swamp, hills, rivers, whatever. 2 weeks later, on 10 Mile Mountain. Set up a “mini-henge” with alignments and pointer to “that hill back there near my Home… “HERE” above.. Now hunt the area for a month. It starts getting cold, cloudy, stormy. I’ve got 40 lbs of dried jerky. Time to head home. But it’s been a month or three and the sun has shifted and it’s foggy in the valley on the far side of 10 Mile Mountain. OK, can’t see “Home HERE”10 miles away… but that mountain I’ve been hunting all over is a half day hike to the top. At the top, still overcast and can’t see a thing. But my stone ring tells me “Head down THIS side” and I head off (with my “came here” landmarks map to get me back to Home mountain…)

    It ought to work at all times in all sorts of weather. Even if you get disoriented, all you need to do is spot the ONE mountain you picked on the way in… from any side…

    Of course, on clear sunny days with nothing obscuring the view, you can just spot “Home HERE Mountain” over there and head that way…

    The other feature, of course, is that with the stone waypoints marked on your map, and the ‘valley landmarks’ marking the way through the valley, you can now get home, plop your 40 lbs of jerky on the table, heft a mug of ale, and tell your neighbor he can find a lot of elk “two stone circles” away on this map… that you will share for only another gallon of ale ;-)

    FWIW, there are stories of folks doing something like that (makeing navigation circles) around the South Pacific. IIRC, this site is one of them:


    Happy Hiking… and don’t forget to take a shovel ;-)

    BTW, the Kiwis have built a replica StoneHenge too:


    So I’m not the only one who wanted his own Henge ;-)

  10. Pingback: Unifying The Cubits The Yard and The Rod « Musings from the Chiefio

  11. Aunt Raven says:

    Are you in the UK or the USA ? if in the UK i might have a comission for you in the Forest of Bowland… no promises. I like your style, you are a fine artist.

    [Reply: I'm in the USA but qualify for either a UK or Irish passport... and don't mind travel for work... ]

Comments are closed.