Understanding The Sundial

The Oldest Way To Tell Time!

Most of us have seen sundials but never gave them much thought.

sundial sunset

The most common sundials are often perched on a pedestal of some sort and are found in gardens, common areas, tourist sites, or on one’s back patio.

Sundials offer more than an ornamental value because if correctly placed, they will tell you exactly what time it is based on the shadow cast from the sun. 

The time is correct even to the minute!

What is a Sundial?

A sundial is an instrument that tells us the time based on the position of the sun.

garden sun dial

To better understand how a sundial works, first, we will describe the components.

Components Of A Sundial

Dial Plate

  • This is a where you will see the lines that indicate the hour/minute.
  • Flat
  • Circular
  • Other varieties include vertical or curved.


  • This points due north to the Northern Hemisphere.
  • The angle this forms on the dial plate is equal to the latitude of the sundial location. This allows accurate movement of the shadow as the sun passes overhead.


  • This sits above the style and is what’s used to cast a shadow onto the dial plate to show what time it is.

Hour Lines

  • These are lines on the dial plate that indicate the hour.
  • Some sundials have sections between each hour broken down into 5 or 10 minute increments.


  • The shadow that is cast on the sundial from the gnomon lines up with an hour/minute line on the dial plate and this is how you tell time.


  • The type of time that sundials keep is solar time, similar to military time.
  • Solar time is not the same time that traditional clocks keep.

How To Tell Time On A Sundial

  • Must be a bright sunny day (daylight, not evening)
  • Locate the “hour lines”
  • Locate where the shadow falls on the dial plate, and this will tell you the time.
  • Some sundials have sections between each hour broken down into 5 or 10-minute increments. If not, then you will need to estimate what the minutes are.

History Behind The Sundial

The Universal Sundial was invented by Theodosius of Bithynia (around 160 BC.)

theodosius of bithynia

He was a scholarly mathematician and astronomer, and the combination of both skills allowed him to utilize his celestial mechanics coming up with a way to tell time by the sun’s position in the sky.

Following suit, Emperor Augustus erected a huge sundial in Rome in 10BC.

It stood almost 100 feet tall. By the middle ages, sundials began to crop up in various styles, and designs.

Once the mechanical clock was invented, the use of the sundial began to decline.

Notable Sundials Worth Seeing


Jaipur, India is home to the world’s biggest sundial which is named “Samrat Yantra.” Known as a “Jantar Mantar,” this sundial is one of five in India.

samrat yantra

Jaipur, India is home to the world’s biggest sundial which is named “Samrat Yantra.” Known as a “Jantar Mantar,” this sundial is one of five in India.

Samrat Yantra is located in one of the most sophisticated ancient astronomical observatories.

This observatory was built in the 1700s from stone, bricks, marble, and bronze. It covers about 59,000 square feet.

"Taking sundials to the next level: 2 seconds accuracy.

The Samrat Yantra at the Jantar Mantar in Jaipur (CC BY-NC-ND 2.0)


“Sundial Bridge” is a sight to see in Redding, California. Engineers and designers combined art and architecture to produce a bridge that is a working sundial.

sun dial bridge

The large arc (gnomon) casts a shadow into the arboretum where one can see what time it is.

This shadow moves one foot per minute.

Sundials Require Calculations

Most would never choose to dive into the variables and calculations of sundials because it is usually above the average person’s skill level.

We will save that for those that “live on the edge” with longitudes, time meridians, celestial mechanics and declination arcs!

It is safe to say, unless you have an advanced skill set that leans towards the physics of time, don’t purchase a complex sundial but stick to the simple ones.

sundial by flowers

Otherwise, you may find yourself extremely frustrated.

As earth spins, the sun seems to move across the sky when in fact, we are the ones moving, not the sun!

The angle of the earth’s rotation changes and as a result, corrections (calculations) must be done to sundials to make up for the change.

Fun Facts About Sundials!

  • Solar time is similar to military time.
  • The largest sundial that ever existed was built in 1724 and is located in Jaipur, India where it covers one acre!
  • Sundials are less effective in England as compared to the Mediterranean.
  • The gnomon was named after a stick that was used by nomadic people that called it a shadow stick. They were able to judge time by the length and position of the stick’s shadow.


(n.d.) Solar vs. Local Time, Ball State University, Retrieved from:

(n.d.) Sundials Ancient Clock, Science IQ, Retrieved from:

(n.d.) Sundial History, First Time Keeping Device, Retrieved from:

(n.d.) Where is the Jantar Mantar Home of the World’s Largest Sundial?, Retrieved from: