Frequently asked questions
We welcome queries on sundials - if we cannot answer them ourselves, we can usually suggest someone else who can. We've grouped together some of the queries we have received and the answers we gave then - maybe some of them may be relevant to your question too.
Q43. What i s the best book or web address which can tell me how to construct an Armillaary sundial
"Sundials - Their Theory and Construction" by Albert E. Waugh is a very comprehensive and well-written book on the subject, and is available in paperback. Chapter 17 deals with armillary spheres.
Q42 - I just want to ask you the size of the biggest sundial in the world
The big sundials I know about are:
Pajala in northern Sweden - there is I think a link from Sundials on the Internet - use the search facility on the home page
Jaipur in India - there is a full description on the Jaipur sundial trail page
There was also a plan to construct a very large sundial in the easternmost point of New Zealand but I dont know if it got built
Q41 - HELP - My 8yo has a project to do a sundial. The problem is ,in the northwest Puget Sound area it rains alot and it is difficult to do one without the sun. Any suggestios?
Under Nicholson's law, the areas of the world with most sun have fewest sundials, eg Arizona, Mexico, Southern Spain, Greece) and the areas with the highest rain/snowfall have most (eg England, French and Swiss Alps, northern Spain)
Q40 - Hi, I'm a 16th C re-enactor and would love to get my boyfriend an authentic timepiece (untill he aquires the money for a subdermal watch implant !??) I can't seem to find out if either equinoctial sundials, or 'peasents' ring' sundials were in England in the 1500s, as I understand it shepherds' sundials were. I'd be grateful for any help you could offer.
Cylinder dials go back a long way - there is one mentioned by Chaucer and quoted in the book by Waugh. Mrs. Gatty's book says they go back to the 13th cent. (probably also based on Chaucer).
As far as I can remember they got really common in the 18th century, when modern notions of time were beginning to creep in, but the technology for measuring it was (?mercifully) much less sophisticated than it is today.
The people who could give you more information are at the Museum of the History of Science in Oxford.
Q38 - Please can you tell me where I can get some information? Everything I find is for the northern hemisphere!
Yes, it's true, but there are only two important differences, that the gnomon points at the south celestial pole, and that the hour numbers go round the dial in the opposite direction to the Northern hemisphere. But everything else is exactly the same. For example, the gnomon's angle and the angles of the hour lines are related to the latitude in exactly the same way as in the northern hemisphere. Some computer programmes will print out for the southern hemisphere as well as the northern A very good book on sundials, written specifically for the Southern Hemisphere, is available.
Q38 - I have seen every sundial website there is, but I want to know what materials I need to make a horizantle sundial. My school is building a sundial in the front of our school. This is a project that is very important to our school besides our aviary, green house, butterfly garden, and waterfall. We all would really apprecaite it if you would send us some information.Thanks from the kids at West Hernando Middle School
Lovley to hear from you, but the answer is to look round the website first! We try to answer all Emails but usually cannot do so immediately, so it is worth having a good look for what you want (in this case, our projects page)
Q37 - How do you set up an equatorial dial
Setting up an equatorial dial is essentially the same as setting up a horizontal dial (see oursetup.htm page, with the one additional step that you need first to set the angle between the gnomon and the horizontal at the same angle as the latitude of the place you are.
Q36 - 01 Aug I am stuck on a question for a quiz, is there any chance you could tell me what the indicator which casts a shadow on a sundial is called?
The gnomon. Strictly, the gnomon is the indicator and the edge of it which casts the shadow is the style.
Q35 - Can you please tell me the name for the art of making sundials?
The art is gnomonics and the people who do it are gnomonists according the dictionary, but it is a mouthful to say, so many people prefer dialing and dialists.
Q34a - Are the E.O.T timing figures the same for the southern hemisphere. Thanks in advance.
Q34b - I have made a sundial but it does not appear to be particularly accurate. Do I need to make any adjustment to the equation of time because I live in the Southern Hemisphere?
No - the sun is so far from the earth that the Equation of Time corrections are, for all practical purposes, exactly the same wherever you are on earth. The correction does change slightly on any given date from one year to another because of leap years, so the values given in books are usually the average of the four year cycle. Computer programmes such as the NASS Dialist programme give accurate values for every second of every day for a century or more!
Q33 - will be teaching a carpentry class starting in September. We are studying the Colonial America. I am interested in finding plans and instructions on making a sundial that would be similar to one that would have been used by the early colonies of America. Can you please direct me to a source that could help me? Thank you for your time. Cris
The early colonists would have brought over with them some sundials, mainly horizontal ones, being made in Europe at the time. There are a number of these in museums in North America, see, for example, the Ottawa sundial trail. They would also have brought knowledge of vertical sundials, and there are a number of examples of these too, for example on the Sisters of Charity Convent in Ottawa and also in Quebec and other colonial centres.
Q32 - My question is similar to Question 24 in the FAQ. I am interested in creating a human sundial as part of a schoolground naturalization project in Calgary, Canada (latitude 52). I realize I cannot make a horizontal sundial with a vertical gnomon (person) because it will be inaccurate over the seasons. Your web page made reference to analemmatic sundials being used on lawns in a similar way such that the human gnomon would stand in a slightly different posiion each month to make the correction. Could you tell me where I could get the information on how to make such a sundial? Olympic Heights Elementary School Calgary, Canada P.S. Great Website!
The books by both Rohr and Waugh have ten pages or so on how to construct an analemmatic dial. You can order both of these straight off our books page. The easy way is to buy a kit of instructions from Modern Sunclocks who will work it all out for your exact location for a quite modest fee Hope this helps
PS Thanks for your kind PS!
Q31 - I was wondering whether anybody would be able to tell me where the largest Sundial in Australia is? If you could help me as soon as possible I woulf\d be most grateful. My e-mail address is: email@example.com
Sorry, we just don't know but we would like to, and could even start a largest sundials page! This would include the one at Jaipur in India and at Pajala in Finland.
Q30 - - we live in Stamford, Connecticut USA and have been debating the difference between northern and southern latitudes sundials. Are the 15 degree hour markers equal but opposite in the southern hemisphere? Clockwise v. counterclockwise and can you explain the answer
Q29 - I received a sundial as a gift. I see that the numbers go LOWER as you go clockwise around the dial. Does that mean it was designed for use in the southern hemisphere? Don't know why they would sell that in New York if it's true. But your project on how to construct a horizontal sundial shows the numbers going in the clockwise direction. If the sun goes from east to west by way of the south, as in the northern hemisphere, does it not follow that the shadow cast by anything, a tree, a person, etc., will progress in a clockwise direction as the day progresses? What am I missing?
All the sundial books we know concentrate on the northern hemisphere. The only thing different about the southern hemisphere is that the gnomon points to the southern celestial pole rather than the northern one. The direction of the rotation of the earth is in the same direction in both hemispheres. So you are quite right that a horizontal sundial with the numbers increasing in an anti-clockwise direction will have been designed for the southern hemisphere. In the northern hemisphere, the numbers on a horizontal sundial increase in a clockwise direction (just like a clock!) A very good book on sundials, written specifically for the Southern Hemisphere, is available.
Q28 - What is the art of making sundials called?
According to the Oxford English dictionary, the art is called gnomonics and the person skilled in the art is called a gnomonist. However they are both such moutfuls that most people try and avoid using them! (Incidentally, the word gnomon was first recorded in the 1600s, and was also used to describe a carpenter's square as well as the shadow-edge of a sundial)
Q27 - 14 May 1999 I received a sundial as a gift. It's a horizontal type. The numbers descend as you go around clockwise. I am no expert on sundials but how can that be? Time goes backward as the sun progresses thorough its path. Any suggestions or help? Thanks.
Q26 - 10 May - I teach 8th grade science at Sage Ridge School in Reno, Nevada. I am interested in creating a sundial using an analemma. I am interested in knowing how to calculate the curvature of the analemma for this latitude. I would like to have students create one of these sundials out of plywood next year. Thank you. David Roberts
The theory of central projection analemmatic sundials is explained in a comprehensive paper originally publised in the NASS Compendium by Yvon Masse, and available at http://www.union-fin.fr/usr/ymasse/cpaprc.htm. If you just want the answers, Modern Sunclocks will provide a set of plans for an anelemmatic dial for your precise location.
Q25 - Dear Friends, what a fantastic website. One Q though: why does the gnomon have to be at one's latitude's angle? In Q19 you explain the HOW but not the WHY. Why does a vertical gnomon turn incorrect after a few years? Thanks for your help. Heiner Thiessen
Think first of the day of the equinox. The sun's apparent path from earth is exactly above the equator, and rotating at 15 deg. an hour with respect to the earth's axis. If you make an equatorial dial with the gnomon parallel to the earth's axis and the dial plate parallel to the equator, the shadow will move round the dial plate at exactly 15 degrees an hour. Now move forward to the summer solstice. The sun's path is now 23.5 degrees above the equator. But the plane of its orbit is still parallel to the equator, so the shadow will still move round it at 15 degrees an hour. But now consider both cases when the gonom is at, say, 45 deg to the earth's axis. The shadow will move round this gnomon at a variable number of degrees an hour, not at a constant 15 degrees every hour. The number of degrees in any particular hour will be different at the solstice (and indeed at every other day of the year) from what it was at the solstice. So any mark you make on a dial plate to indicate the "clock" hour will not be true after even a few days. I hope this helps. If you want a practical demonstration, put a vertical pole in the ground, and mark where the shadow is at any time other than noon - then mark the same time at intervals over the next few weeks. You will see it for yourself. (You will find a fuller explanation on equation.htmunder the Inclination of the Ecliptic.
Q24 - I am a Landscape Architect in Omaha, Nebraska. I have designed a human sundial to be installed in a public park but am having problems finding the correct settings. Can you help me find someone to do that?
Q23 - I am a sculptor working on a proposal to build a 26 foot high marble and stainless steel column which would function as a sundial. I am not sure what the best method for laying out the hour marks is. I would appreciate any information that you could give me.
Very tall sundials have problems all their own, partly because the gnomon may not be straight due to self-weight, and partiy because the shadow gets fuzzy if it is a long way away from the hour lines. So you need to do a bit of experimenting. You can see a picture of one I did at Lincoln linked from my entry on ......../personal.htm This was only 5 m. high. You also need to understand quite a bit about the theory of sundials, and for this you need 2 or 3 of the books listed on .........../books.htm You can get most of them through amazon.com
Q22 - Can you tell me, can I construct and arrange a vertical sundial facing due north the same way as a sundial facing due south as illustrated within these pages. I live in the southen hemisphere and I wish to make a vertical sundial but our aspect faces due north. Any assistance will be welcome
-/ I always get slightly muddled about the southern hemisphere, but the essence of it is that the gnomon has to be parallel with the earths axis. In the northern hemisphere, that means it points at the pole star. In the southern, it points at the southern celestial pole, and the sun appears to go round it at 15 deg per hour just as everywhere else in the world
Q21. . I have read your "How to set up a horizontal sundial" page with interest. Surely, if one's sundial's gnomen is correct for one's latitude and the clock time correction for one's actual longitude (with respect to the time zone longitude) has been calculated, it is a simple matter to let the sundial do it for you. Simply set the sundial so that it shows the local sun time, taking into account the equation of time. There is no need to rely on noon. This could be done in the morning and checked at intervals during the day. I all is OK the sundial's noon line should point to the celestial pole.
Yes, you are quite correct. Why we do not recommend doing it this way is that most horizontal dials are not sufficiently accurate to do it this way, because the gnomon does not have a square edge, the lines are too wide, and/or the gnomon not quite straight. It is also quite rare to find a "garden-centre" sundial which is correctly set for its latitude. So we thought it preferable to set the thing out right to start with, and let the minor inaccuracies sort themselves out.
Q20. I live in Israel which is approximately 32 degrees north. I have made a sundial according to my latitude. What I would like to know is whether the graphs for correcting the discrepancy of a sundial are the same all the world over, or change from place to place. (I have a copy of a graph from Enland - would it be valid here?) Also, how do I adjust for differences in longitude within the same time zone? I hope you can help me or guide me to the right source on the web. Thanks in advance, Jonathan
Thanks for your message. The Equation of Time is universal. The distance to the Sun is so much greater than any distances on earth. If you want your sundial to show the time at your prime meridian, you work out the time difference at 60 minutes of time equals 15 degrees of rotation. So, Lowestoft is at 1 deg 20 East, so the correction is 5 mins 20 secs. The sun reaches Greenwich after it reaches Lowestoft , so if I want the Lowestoft dial to read Greenwich time, I must calculate the hour lines for 12.05.20, 1.05.20, 2.05.20 and so on. I hope this will help you. If it does, let me know, and I will post it on our FAQ page to help others.
Q19. I have a couple questions about the gnomon on a sundial. How long should it be, and is it's angle calcualted from the latitude, or is it taken directly from latitude (my lat is 33.6, should the angle be 33.6 degrees)?
A19 - The gnomon always has to point at the celestial pole. if you are at the North (or South) pole, it therefore points straight up if you are at the equator it is horizontal. as you move north (or south) from the equator, the gnomon angle lifts up from the horizontal and the latitude also increases. So, If it is a horizontal sundial, the angle between the gnomon and the horizontal is equal to the latitude If it is a vertical dial, the angle between the gnomon and the vertical is equal to the co-latitude ( or 90 degrees less the latitude)
As to how long it should be, you can calculate it, because the sun's orbit dips 23.5 deg below the equator in winter and 23.5 above it in summer. You want to make sure that the shadow falls all the way across the dial plate when the sun is highest - on midsummer day. Get your maths teacher to help you out with how to calculate it if you cant work it out for yourself. Hope this helps
Q18 - I am looking for information on setting up an armillary sundial. I have taken it apart and restored it. On setting it up I need the longitudal and latitudal figures. I can't find the information of the internet. Please help me.
Please refer to our page on "Setting up a horizontal sundial". Setting up an armillary is essentially the same - the axis (gnomon) has to point to the celestial pole, which means that the angle it makes with the horizontal has to be equal to the latitude of the place, and the projection of the gnomon on the horizontal has to be pointing to true north, ie along the local meridian.
Q17. Dear Mr Sundial, I have a sundial with a gnomon set at 52 degrees, which is obviously an incorrect setting for is location which is 39 degrees 35 minutes South, and 174 degrees 16 minutes East. Could you please advise me of the correct setting given that New Zealand Standard time is G.M.T. plus 12 hours. Thanking you in anticipation. Could you also enclose your "snail mail" address so I can send you a 1999 New Zealand calendar in appreciation. Frank Lacy,
Thanks for your message, You too should refer to ....../setup.htm. For horizontal sundials, setting in the southern hemisphere is essentially the same as setting in the northern hemisphere, except that the gnomon is pointing to the south celestial pole. So you need to wedge up the sundial in such a way that it thinks it is at 52 deg. South. Your sundial is certainly manufactured for a place exactly on a standard meridian, and you cannot adjust for this (see next Q). You just have to remember to add or subtract the appropriate amount (4 mins for every degree you are away from your standard meridian). If you want to convert exactly to "clock time", you will also have to add or subtract the Equation of Time (see ....../equation.htm). I would certainly appreciate a calendar. Thank you. Would you also like to write a sundial trail for your neighbourhood (see ......./sunlist.htm)
Q16. we live in Langhorne, Pennsylvania, and we are affected by the daylight savings time. we put a sundial in our backyard, and my father and I had several long talks regarding adjusting or not adjusting the sun dial for the daylight savings time. please put us out of our misery, by answering this strange question.
thank you, heather and kenneth pyle
Please refer to www.sundials.co.uk/setup.htm for a full answer. The short answer is that it's best to set it for your local noon, and then to remember when you read it that you need to adjust it by XX minutes to get the time at your standard meridian, and a further hour if it's in the summer.
The reason for this is that the angular difference between successive hours is not uniform. So rotating the dial will lead to inaccuracies. This may not matter too much if the gnomon of your sundial doesnt have a square edge, or if the hour lines are engraved too wide as many mass-produced dials are.
You should also check what latitude the sundial you have is designed for, and if necessary make the adjustments in ......./setup.htm
Q15. I have recently moved to NSW Australia and whilst touring the local area spotted a sign at 'Singleton', which states 'Worlds Largest Sundial', having visited the 'Observatory' at Jaipur, India a few years earlier who had the same claim, I realised that one of them must be wrong. Both were of a similar design, but certainly the one in India was considerably larger. Perhaps you would like to list them, but as to which is the 'Worlds largest', I will leave to you!
I would like to try and get details of the size of the one in Jaipur, and if it is larger I will show this to the local tourist information centre! Any ideas where I might find this information? Do you know which is the Worlds largest sundial, perhaps neither of those I have mentioned. I am finding the general 'Sundial' information fascinating.
Thank you Sue Spence
The large instrument - a mammoth structure - is called Brihat Samarat Yantra and the main part is a right angle triangle with a base of 44 metres and a gnomon angle of 27 degrees, so the height is 27 meters. The semicircular quadrants have a radius of 15 meters. There is a link to it on the pix.htm page. There is another big one at Pajala in Sweden written up in the penultimate issue of the British Sundial Society Bulletin no 97.3. It has a diameter of 39 metres, so I guess that is not the biggest! (Paul Fischer has kindly given us its URL: http://www.pajala.se/narliv/ftgreg/elcs/elcs.htm and there is a description of it at http://www.pajala.se/welcome/tourism/soltorg.html
Q14. I am a member of the British Sundial Society and have built dials but I am still a beginer and one question remains in my mind that I can not seem to find the answer for. There seems to be a bit of a clue in question 1 in the F.A.Q. document but it is still not clear to me.
If the angle of the earth changes from Summer to Winter then why is the axis of the earth always quoted as pointing to the pole star?
The answer to your question is in what the angle is changing relative to. The angle of the earth's axis relative to the far distant stars doesnt change at all as the earth goes round the sun. But the angle relative to the sun does. In midsummer the axis is tilted 23.5 degrees towards the Sun, and in midwinter, it is tilted the same amount away from the sun.
Q13. Dear Society, What I would like to know is how Sundials work throughout the seasons. I mean the noon shadow falls in one place in Summer and a totally other place in Winter. Could some one explain this very rudimentary fact to me? I have just purchased my first sundial and would like to set it up correctly.
A13. Dear Susan Thanks for your message. Try looking at setup.htm on www.sundials.co.uk Essentially, at a given time of day in winter, the sun is lower in the sky and at a different angle relative to south compared with the same time of day in the summer. The slope on the gnomon, which is equal to the latitude, compensates for this, so that the shadow, taken from the lower part of the gnomon in winter and a higher part in summer, falls in the same place at the same hour. Let me know if this helps you. If so, I will put it up on the FAQ to help others. Thank you so much for your help. Susan
Q12. Do any of your visitors ever tell you if they got useful information from it?
Yes, occasionally. It's obviously only a very small fraction of those who visit Sundials on the Internet, and it's a great pleasure to get E-mails like this example:
Q11. I think this page is really great. When I got the project of making a sundial I didn't know where to start until I found your web site explaining how to make a sundial. I found that it was really easy to make and I hope now to get a good make for my project.
Thank-you Jennifer (one very happy person!)
Thanks a million. It's so nice to get a letter like yours - it makes the whole thing worth while. So I'm another very happy person! Webmaster - Sundials on the Interent
Q10a. We are doing a schools project on sundials and would like some help
Q10b. we are doing an assignment for school and wish to construct a sundial our latitude is 38deg 23' how do we plot the hour lines ?
Q10c. I'm a student at a high school and want to know alot about sundials. This information is needed for a science final and would be greatly appreciated if you could send it immediately.
There are details of a suitable project on www.sundials.co.uk/projects.htm if you have to get started immediately.
If you have more time, we would suggest obtaining "Make a Sundial" from the British Sundial Society which has a number of projects. It was produced specifically for schools, but is equally suitable for anyone seeking to gain understanding of sundials and experience in making simple models before venturing on to larger projects. It can be ordered directly from them
Q9. I want to give my daughter some help on a project on the history of sundials, but can't find anything in my public library
Sundials - History Theory and Practice by Rene RJ Rohr has a very good section on the history of sundials.
Q8. My son is doing a science fair project on sundials. We are unable to locate a list of most famous sundials, and their location so that we can pinpoinnt them on a world map. Any help would be appreciated.
There is no comprehensive or easy way of finding out this kind of information. Some of the books give lists of sundials in particular areas. Our own pages on favourite sundials in North America, in the United Kingdom, in France, and in the Netherlands will also be helpful. And there are links to pictures of other sundials on the Internet on pix.htm. We are building these lists up gradually - if you find them helpful, please help us by adding any information you have!
Q7a. I am keen to make a sundial but know very little about it.
Q7b. I don't know if you can help me, but I want to construct a vertical sundial similar to some I saw in the U.K. I am particularly interested in a sundial that tracks the four seasons. Any construction details, geometry, and advice (pictures of vertical sundial faces?) would be greatly appreciated. My house faces south and I have the perfect location for such a sundial. Can you help?
If you want a few small practical projects to do before you get involved with your first big individual project, your best course is to get "Make a Sundial" (see question 1 above). This will give you a good basic grounding. Or you could start off with the projects on ...../projects.htm
Q6. I acquired a Shepherd's watch but don't know exactly how to use it. CAn you be of any help? Thanks, Ann
There us a very good sundial mailing list which is the best way of getting quick and definitive answers to detailed technical questions like this. You can find out how to post a question (and how to subscribe to the list if you want) on www.sundials.co.uk/mailist.htm. Please start your enquiry along the lines "I found out about the mailing list from the FAQ page on Sundials on the Internet"
Q5. Are there any internet sites on the theory and/or constuction of sundials? if so, where? How does their constuction differ from the northern to southern hemispheres?
Try the sites listed on equation.htm. But you will probably find you are better off with one of the books listed above or on books.htmA very good book on sundials, written specifically for the Southern Hemisphere, is available.
Q4. I am a student in Singapore and I would require instructions to make a sundial for latitudes of 0 degrees, please email me immediately.
Most of the literature about sundials is written by people in medium or high latitudes. There, the gnomon (which has to point to the celestial pole) makes a large angle (some 50 deg in England) with the horizontal. At low latitudes, the gnomon makes a very small angle with the horizontal, and on the Equator, the gnomon has to be parallel with the dial plate. If you go to the botanic gardens in Singapore, they have a really nice sundial there and you could copy that using simple materials. Essentially you have a flat plate projecting p cm. from a horizontal surface with the hour lines. The hour lines are placed at y= p x tan h where h is the hour angle which is 15 deg for 11 am and 1 pm, 30 deg for 10 am and 2pm etc It could last a lot longer than 30 days.
He replied: I have made the sundial and it is quite accurate. Another victory for Sundials on the Internet!
Q3. Where and Which is to largest sundial on this planet? Where is the oldest sundial still in tact? Curious is the cat!
I should think the one at Jaipur India is probably the largest. This is another of the questions worth posting on the sundial mailing list See question 5. above
Q2. Please could you send me details about where I can buy a sundial. I know this is a bit cheeky, but I am having great problems finding a stockist. I would be very grateful if you could help me in this matter.
The easiest place to buy a sundial is at a garden centre, or from a mail order catalogue like the one from the Science Museum in London. But you should read How to set up a horizontal sundial first so that you know how to check the gnomon angle, and how to correct for it if it is not right for your location. The accuracy of these dials is often very poor because the gnomon is not straight or the hour lines are wrongly marked out. For a more accurate sundial, you should go to one of the sundial makers listed on our sundial makers and designers page
Q1. I am a reference librarian at the Flagstaff, Arizona Public Library. A patron has requested information about the Dial of Almaraz. This is supposedly a 15th Century European sundial (in Almaraz, Spain?) which uses a room and a window or a portion of a building as the mechanism of the sundial. We have consulted many different sources, but have been unable to locate any references.
See question 6. above