MADE FOR PIONEERS

How to read the time with a sundial

How to read the time with a sundial
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Telling Time with the Sun: A Practical Guide to Sundials and Ancient Timepieces

By A. Fost

I remember the first time I truly grasped what it meant to read time from the sky. It was a spring afternoon in southern France, and I was standing beside a weatherworn sundial carved into a limestone wall, the shadow of its gnomon creeping steadily across the hours. No ticking. No screens. Just the turning Earth and a quiet line of light. It was humbling.

Ever since, I’ve been collecting conversations with those who still know how to tell time with the sun, horologists, astronomers, historians of science. What follows is my attempt to gather their insights into the most accurate and accessible guide to understanding solar time and reading the oldest of all timepieces: the sundial.

 

 

What Is Solar Time?

To begin with, solar time is simply the time kept by the Sun itself. Unlike our modern clocks, which slice the day into 24 equal hours, solar time is based on the actual position of the Sun in the sky.

Dr. Clara Menard, an astronomical historian I met in Geneva, put it like this:

“Solar time is true time, the time your body instinctively knows. It’s noon when the sun is at its highest. Everything else is a compromise.”

Sundials are the original instruments of telling time with the sun, and understanding how to read one reconnects us to a rhythm far older than any digital display.

 

 

How a Sundial Works: The Elegance of Shadow

At its essence, a sundial consists of two parts:

  • The gnomon, the piece that casts a shadow, often angled like a blade

  • The dial plate, which holds the hour markings

The gnomon must point toward the Earth’s rotational axis, that is, true north in the Northern Hemisphere or true south in the Southern. Its angle must match your latitude; in Paris, for example, the gnomon would be tilted about 48° above horizontal.

“The mistake most people make,” said Étienne Laroque, a garden sundial restorer in Provence, “is to treat sundials like ornaments. But a sundial is a precision instrument, if you give it the respect of proper alignment, it will tell you real solar time, to the minute.”

 

 

Setting Up a Sundial Correctly

To make your sundial more than a decorative curiosity, follow these steps:

  1. Find true north. Use an app or compass or an Augé watch.

  2. Align the gnomon. Tilt it at an angle equal to your local latitude.

  3. Level the dial plate. Even a small tilt can introduce significant errors.

Once set, your sundial will begin its slow conversation with the sky, casting the shadow that tells you solar time.

 

 

Reading Time on a Sundial: A Daily Ritual

To read the sundial:

  • Note where the shadow of the gnomon crosses the hour lines.

  • That’s your apparent solar time, the Sun’s actual time at your location.

But here's the twist: solar time and clock time rarely agree. Because of Earth’s elliptical orbit and axial tilt, there can be up to a 16-minute difference between them. That brings us to…

 

A Contemporary Expression of Solar Time

Working within Augé, I’ve often found myself returning to the sundial, not as a relic, but as a reference. Its simplicity, its reliance on elemental truths, continues to inform how we think about time.

The “Since 4.6 Billion Years” timepiece was born from that same reverence. It’s not a reinterpretation of the sundial, but a parallel gesture, a modern instrument that reads the hour using the sun’s position and the Earth’s magnetic field. There is no battery, no circuitry. Just orientation, light, and time.

It’s a different kind of timekeeping, slower, participatory, more attuned.
 For those who appreciate the ritual of reading a sundial, this offers a way to carry that same intimacy with solar time, wherever you go.

 

Converting Solar Time to Clock Time

There are three simple corrections to translate sundial readings into your local time:

1. Longitude Correction

Standard time zones assume a central meridian (e.g., 0° for GMT, 15° for CET). If you live east or west of that, adjust by 4 minutes per degree.

2. Equation of Time

A seasonal correction based on Earth’s orbit. You can find this value for any date from websites like NOAA's Solar Calculator. For example, March 26 typically requires a +5 minute adjustment.

3. Daylight Saving Time (DST)

Add 1 hour if DST is in effect.

Example
 Your sundial reads 1:20 PM on March 26.

  • You're 2° west of your time zone's meridian → –8 min

  • Equation of Time: +5 min

  • DST in effect: +1 hour

Corrected clock time = 2:17 PM

“The sundial doesn’t lie,” says Dr. Menard. “But you have to understand its dialect.”

 

 

Why Telling Time with the Sun Still Matters

You might ask, in the age of atomic clocks and smartphones, why bother?

Because telling time with the sun is not just practical, it’s deeply human. It reminds us that timepieces were once crafted to reflect the turning of the Earth, not to enslave our schedules. It slows you down. It grounds you.

And in a world obsessed with precision, there’s wisdom in returning to the source.

 

 

Final Thoughts: Relearning the Language of Light

There’s a quiet dignity in standing beside a sundial, watching the world spin beneath the sun. When you read solar time, you aren’t just marking hours, you’re participating in a dialogue older than history.

So if you have a sundial, dust it off. Align it. Observe it.
 If you don’t, make one. Even a stick in the ground and a few well-measured lines will do. Because to tell time with the sun is to return, however briefly, to a time when we listened more carefully to the world around us.

 

 

Resources for Solar Time Enthusiasts

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A. Fost

Welcome to MADE FOR PIONEERS. I explore the marks of time, from nature to the cosmos. My curiosity often leads me to unexpected subjects. These notes fuel the inspiration behind Maison Augé, creator of timekeepers and measuring instruments inspired by natural mechanisms.

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