The Gnomon Sun Path and Analemma Lab: Exploring Day Length and Noon Altitude

What is a Gnomon?

A gnomon is the part of a sundial that casts a shadow. It's essentially an upright rod or stick set at a specific angle to align with Earth’s axis, allowing it to cast shadows that indicate time and position in the sky.

The term 'gnomon' comes from ancient Greek, where it referred to both the instrument itself and the mathematical concept of division.

Understanding Sun Path and Analemma

The path of the Sun across the sky varies throughout the year due to Earth's axial tilt and its elliptical orbit around the Sun. This variation is captured by the analemma, a figure-8 pattern that represents the position of the Sun at solar noon over the course of a year.

By adjusting latitude and date in our simulation, we can observe how these factors influence day length and the altitude of the Sun at midday.

Seasons and Day Length

The changing seasons are primarily caused by Earth's axial tilt. As Earth orbits the Sun, different hemispheres receive varying amounts of sunlight due to this tilt, leading to differences in day length and temperature.

In the Northern Hemisphere, summer occurs when the North Pole is tilted towards the Sun, while winter happens when it’s tilted away.

The Equation of Time

The equation of time accounts for the discrepancy between solar time (time based on the position of the Sun) and mean solar time (average time over a year). This difference arises from Earth's elliptical orbit and axial tilt.

By manipulating the simulation, we can observe how changes in Earth’s orbital parameters affect the equation of time.

Frequently asked questions

Try it live

Everything above runs in your browser — open Gnomon Sun Path and Analemma Lab: Day Length, Noon Altitude and Shadow by Latitude and Date and change the parameters while it is running. Nothing is installed, nothing is uploaded, the whole model lives in one tab.