Border Sundials

Handmade Sundials & Armillary Spheres

“A garden to walk in and immensity to dream in – what more could he ask? A few flowers at his feet and above him the stars.” – Victor Hugo, Les Miserables

Take a look at our latest Sundial of The Month.

  • Shop
    • Sundials
    • Plinths
  • Armillary Spheres
    • Brass
    • Verdigris Armillaries
    • Stainless Steel
    • Prices
    • Gallery
  • Horizontal
    • Buy Horizontal Sundials
    • Gallery
  • Vertical
    • Gallery
  • Plinths
    • Buy Plinths
    • Gallery
  • Prices
  • About Sundials
    • History of sundials
    • Theory of sundials
    • Quotes for sundials
    • How Do Sundials Work
    • What is the Equation of Time?
  • News
  • Contact
    • Enquiry Form
    • Download Brochure
    • Order Printed Brochure
    • Testimonials

How Do Sundials Work

Since pre-history people have regulated their lives by the apparent motions of the Sun and the shadows cast it casts on the ground (See our History of Sundials). Of course we all know it’s really the rotation of the Earth on its axis which causes the shadows to move, but for convenience we say the sun moves.

For every degree that the Earth rotates, the sun appears to move one degree across the sky. It takes the sun 4 minutes to cover 1 degree, and an hour to cover 15 degrees, therefore 360 degrees or one full rotation in 24 hours.

If you know this and where South is, you have all you need to tell the time. Let me explain: The Sun goes round the Earth in 24 hours. Therefore if it is due South at midday, and due North (hidden from us by the Earth) at midnight, then at 6am it must be due East, and at 6pm it will be at due West. If you look to the South, East is over your left shoulder and West on your right shoulder, so it is easy enough to estimate the angle of the sun between these points and guess the time. Possibly not good enough to keep an appointment, but a good trick, and you get better with practice.

sun time copy

A sundial is a device that tells the time of day by measuring this apparent movement of the Sun accurately. The simplest sundials consists of a flat plate (the dial) and a shadow caster (the gnomon) which casts a shadow onto the dial. As the sun appears to move across the sky, the shadow aligns with different hour-lines which are marked on the dial to indicate the time of day.

The gnomon usually casts a broad shadow so that it is easy to see, however this can lead to uncertainty over which side of the shadow to read. To avoid this one side is usually curved and the style will be a straight line which lines up with the hour lines.

On more complicated sundials the gnomon may also be a rod (like an armillary sphere), a wire or anything else (such as your own body).

The style of the gnomon must be parallel to the axis of the Earth for the sundial to be accurate throughout the year. Therefore the style’s angle from horizontal is equal to the sundial’s geographical latitude.
You can see from this picture that a sundial on the equator would have a gnomon angle of 0 degrees, while one on the poles would have an angle of 90 degrees.

latitude variation

Longitudinal Variation

Using the sun’s light to cast a shadow onto the hour lines, sundials tell ‘Local Apparent Time’ rather than ‘Mean Time’ as conventional clocks do. To make modern life work, the world is divided into time zones and our clocks are set to national or regional time (GMT for the UK).

For each degree of Longitude to the West of Greenwich (or your local meridian) the sundial will appear to be four minutes slow and for every degree to the East it will appear four minutes fast. This is the time it takes the sun to travel one degree, and is known as Longitudinal Variation.

longitudinal variation

Daylight Saving

Sundials do not understand daylight saving time, so in the summer you will need to add an hour onto the time shown to take account of British Summer Time.

By adding or subtracting the Longitude Variation and the Equation of Time you are able to read GMT at any position in the country.

The Equation of Time

Longitudinal variation and Summer Time are fixed and easy to understand. Much more complicated and deserving of it’s own page is The Equation of Time.

Order A Sundial


Order one of our horizontal sundials in our store today.

Subscribe to our News

Equation of Time

Today your sundial will appear to be running 2 minutes and 12 seconds fast against GMT. (Please add an extra hour for British Summer Time.)

More info:
How do Sundials Work?
What is the Equation of Time?

Testimonials

Thank you it was as described and just what I expected, posted and delivered promptly
Absolutely delighted. Very special.
Lovely item. I asked for the wording to be arranged slightly differently and there was no issues. Thanks
Sundial is beautiful
Kepler was excellent, delivered within a few days of ordering and looks fantastic!
Very pleased with the engraving as it is to be a special gift and it looks lovely
Very happy with the product – it was good quality and very pleased with the lettering
Bought this for my husbands birthday and he was delighted with it. Great communication with seller and fast delivery
Beautiful sundial, lovely quality, well-packaged, very pleased with purchase!
A special personalised wedding gift exactly as portrayed in the picture – a great success

Contact

Border Sundials
Chapel Farm
Clytha
Abergavenny
NP7 9BW

T: 01873 840 297
E: office@bordersundials.co.uk

Download A Brochure

Recent Posts

  • Vertical Sundial at The Charter House, London
  • Quitsato Sundial – El Reloj Solar Quitsato
  • Guillaume Le Gentil
  • Incised Sundials at Mersham Church, Kent
  • Wills’ Cigarette Cards

Facebook

Border Sundials | Promote your Page too

Tweets

  • There's sill time to take a look at April's #SundialOfTheMonth, the #CharterHouseSundial. https://t.co/t4oso5jWOp https://t.co/Q9a4l37Mbm about 6 hours ago
  • Today your sundial will appear to be running 2 minutes and 12 seconds fast. #equationoftime #sundials about 6 hours ago
@bordersundials

Instagram

Load More...
Follow on Instagram

© Copyright 2018 Border Sundials · All Rights Reserved · Site by Peter Mahoney