Sundial
A sundial is an instrument used to show the time of day. It does so using a spike or triangle (a gnomon) that protrudes from a horizontal or vertical plate, casting a shadow which indicates the time. It is one of the earliest devices relating to the study of time (horology) and was used by the ancient Egyptians and Babylonians (1500 BC). The art or science of constructing sundials is called this gnomonics, named after the central part used to cast the shadow.
Solar time is derived from the Sun's position, by counting one hour of time every 15° of hour angle, as Earth is rotating around its axis once every 24 hours, which gives 360°/24 h = 15°/hour. On a sundial, the noon line corresponds to the moment of culmination of the Sun, when it crosses the local meridian. This sort of time depends on the location or longitude. The designer must calculate a longitude correction for a given location, by comparing the longitude to the reference meridian (CET meridian is 15° East). For example, the time in Exeter, Devon might be up to 15 minutes later than that in Greenwich. So sundials are based on the equation of time plus a longitudinal correction.
In the UK, the world heritage site, Stonehenge, built in the Neolithic period (2500 BC), is thought to be a form of sundial with each of the 30 upright stones representing one day within a repeating 30-day month. Twelve rotations of the Circle equates to 12 months, forming a solar year (which is 365 days, not 360).
The oldest sundials measuring shorter time cycles to be found in the UK are the tide dial of Bewcastle Cross, Cumbria, dating from the 7th century, and the Boyne Valley sundial in Ireland, a sundial stone believed to be over 5000 years old.
A tide, mass or scratch dial is a type of sundial that has the canonical hours instead or in addition to the standard hours of daylight marked.
Today sundials can be found as features of historical buildings and landscapes, often as single horizontal standalone features in gardens or incorporated into building facades as vertical sundials. Sundials can also be added as interesting features to modern homes or as home educational design projects.
A map showing sundials of interest around the UK can be viewed via The British Sundial Society, along with history, guidance and advice.
[edit] External links
- https://sundialsoc.org.uk/dials-filter/
- https://www.shadowspro.com/en/sundials.html
- https://www.sundialzone.com/en/sundial
- https://www.sunearthtools.com/solar/build-sundial.php#top
- http://www.anselmi.vda.it/home.htm#
[edit] Related articles on Designing Buildings
- Brise soleil.
- Designing daylight solutions for commercial buildings.
- Historic England.
- Listed Building Heritage Partnership Agreements.
- Large scale solar thermal energy.
- Passive building design.
- Protection of historic statues, plaques, memorials and monuments.
- Scheduled monuments.
- Solar photovoltaics.
- Visible light.
Featured articles and news
Design and construction industry podcasts
Professional development, practice, the pandemic, platforms and podcasts. Have we missed anything?
C20 Society; Buildings at Risk List 2025
10 more buildings published with updates on the past decade of buildings featured.
Boiler Upgrade Scheme and certifications consultation
Summary of government consultation, closing 11 June 2025.
Deputy editor of AT, Tim Fraser, discusses the newly formed society with its current chair, Chris Halligan MCIAT.
Barratt Lo-E passivhaus standard homes planned enmasse
With an initial 728 Lo-E homes across two sites and many more planned for the future.
Government urged to uphold Warm Homes commitment
ECA and industry bodies write to Government concerning its 13.2 billion Warm Homes manifesto commitment.
From project managers to rising stars, sustainability pioneers and more.
Places of Worship in Britain and Ireland, 1929-1990. Book review.
The emancipation of women in art.
Call for independent National Grenfell oversight mechanism
MHCLG share findings of Building Safety Inquiry in letter to Secretary of State and Minister for Building Safety.
The Architectural Technology Awards
AT Awards now open for this the sixth decade of CIAT.
50th Golden anniversary ECA Edmundson awards
Deadline for submissions Friday 30 May 2025.
The benefits of precast, off-site foundation systems
Top ten benefits of this notable innovation.
Encouraging individuals to take action saving water at home, work, and in their communities.
Takes a community to support mental health and wellbeing
The why of becoming a Mental Health Instructor explained.
Mental health awareness week 13-18 May
The theme is communities, they can provide a sense of belonging, safety, support in hard times, and a sense purpose.
Mental health support on the rise but workers still struggling
CIOB Understanding Mental Health in the Built Environment 2025 shows.
Design and construction material libraries
Material, sample, product or detail libraries a key component of any architectural design practice.