Making a Sundial/​Fun with Shadows

What is this session about

Phenomena around the Earth-Sun system

Simple measurements/​observations with a sundial can tell us a lot about interesting phenomena

A common misconception

What is the reason for the seasons?

Big ideas

Measuring the circumference of the Earth

What do we discuss in this session?

Starting with simple observations, one can build a lot of understanding about the Earth-Sun system. We discuss such observations and connect them to various aspects of our life on the planet, such as the seasons, the length of the day, the apparent motion of the Sun in the sky, etc.

  1. Constructing a basic sundial
  2. The reason for seasons
  3. Measuring our latitude
  4. Zero shadow day
  5. Measuring Earth’s circumference by doing simultaneous measurements of shadows

00:00 Introduction
06:37 A basic sundial
13:10 Comparing the length of a shadow at noon at Delhi and Bangalore
17:49 A new Pole Star 10,000 years from now
20:36 The reason for seasons
24:56 The Earth is actually a bit closer to the Sun in winter (in the Northern Hemisphere)
27:28 Apparent motion of the Sun in the sky
32:29 Sidereal day vs Solar day
39:33 The Earth’s distance from the Sun is essentially fixed
53:14 Measure your latitude on Equinox day and Zero shadow day
01:00:01 Zero shadow day on the Equator
01:05:09 Recreating Eratosthenes’ measurement of the Earth’s circumference from 240 BC
01:06:47 Types of sundials
01:11:45 A measure of Solar irradiance

Other resources:

Making a sundial

Analemmatic sundial Bangalore

Bangalore noon data

Bangalore-2021-Noon-Data Download

Slides from the session

WPT-Dec-2021 Download