Topic: What is a gnomon and how to use it to observe the apparent movement of the Sun over the horizon?

Target group

Student in class VI‑th elementary school

Corre curriculum

General requirements

I. Geographical knowledge.

1 . Mastering the basic geographical vocabulary in order to describe and explain phenomena and processes occurring in the geographical environment.

II. Skills and application of knowledge in practice.

1 . Conducting observations and measurements in the field, analyzing the data obtained and formulating conclusions based on them.

2. Using plans, maps, photographs, drawings, diagrams, diagrams, statistical data, source texts and information and communication technologies in order to acquire, process and present geographic information.

Specific requirements

V. Earth Movements: Earth in the Solar System; rotational and reciprocating motion; consequences of Earth movements.

Student:

3 . explains the relationship between the rotational movement and the voyage of wandering and sun‑raising, the existence of day and night, the daily rhythm of human life and nature, the occurrence of time zones.

General aim of education

The student will learn to observe with a gnomon the apparent sunward wandering over the horizon.

Key competences

• communication in foreign languages;

• digital competence;

• learning to learn.

Criteria for success
The student will learn:

• you will explain what a gnomon is and how to use it;

• you will describe how to safely observe the Sun with a gnomon;

• You will set geographic directions and the local meridian using the gnomon.

Methods/techniques

• activating

  • discussion.

• expository

  • talk.

• exposing

  • film.

• programmed

  • with computer;

  • with e‑textbook.

• practical

  • exercices concerned.

Forms of work

• individual activity;

• activity in pairs;

• activity in groups;

• collective activity.

Teaching aids

• e‑textbook;

• notebook and crayons/felt‑tip pens;

• interactive whiteboard, tablets/computers.

Lesson plan overview

Before classes

• Students get acquainted with the content of the abstract. They prepare to work on the lesson in such a way to be able to summarize the material read in their own words and solve the tasks themselves.

Introduction

• The teacher determines the purpose of the lesson, informing the students about its planned course.

• The teacher writes the topic of the lesson on the blackboard or interactive whiteboard. Students write it in notebooks.

Realization

• The teacher indicates a person who will demonstrate with the help of the globe changes in the Earth's lighting caused by its rotational motion and reminds the class what is the relationship between the Earth's rotational movement and the apparent solar wandering over the horizon.

• The teacher acquaints students with the risks resulting from direct observation of the Sun. Next, he discusses the method of observing the apparent sun's wandering over the horizon using a gnomon. For this purpose, the lecturer introduces the students to the illustration in the abstract and the animation showing the simulation of the change of shadow cast by the gnomon on the equinox in the northern hemisphere..

• Students individually or in pairs will familiarize themselves with the description of the observation included in the lesson, which consists in designating a local meridian in the neighborhood of the house or school (observation 1). Next, go to interactive exercise No. 2, which aims to strengthen the ability to understand the relationship between the position of the Sun in the sky and the length and direction of the shadow cast by the gnomon.

• The teacher initiates a discussion on the class forum regarding the described method of determining geographical directions. Then he instructs the students to get into teams and perform the described observation and to illustrate it (eg with the help of photos or an amateur film) as part of homework as a student project.

Summary

• The teacher goes to the summary of the lesson, during which the students can ask questions and complete the notes.

The following terms and recordings will be used during this lesson

Terms

Texts and recordings

What is a gnomon and how to use it to observe the apparent movement of the Sun over the horizon?

The apparent motion of the Sun over the horizon is an indirect proof of the rotational motion of the Earth. We can observe it every day.

One of the ways to avoid the risk of damaging your eyes, while following the apparent movement of the Sun, is to observe the shadow cast by objects illuminated by direct sunlight. By observing the shadow, we can make conclusions about the apparent movement of the Sun. Every relatively thin, straight, and vertical rod stuck into the ground becomes a gnomon, i.e., the instrument whose shadow determines the position of the Sun.

The following simulation shows changes in the shadow cast by a gnomon on the equinox day in the northern hemisphere.

The length and direction of a gnomon’s shadow are determined by the height of the Sun and its azimuth. When establishing the directions based on the shadow cast by a gnomon, you should remember that in Poland and in the whole area of the northern hemisphere, except for the intertropical zone, the Sun is always at its highest point on the southern side of the sky. The shadow cast by a gnomon at noon is the shortest and precisely indicates the north. We may conclude from this that the moment of the Sun’s highest point (the moment of the solar noon) has come. When this happens, the position of the Sun in the sky indicates the south. The extension of the line set by the gnomon’s shadow is the local meridian of the point at which the gnomon is stuck into the ground. The sun rises exactly in the east and sets exactly in the west only twice a year (March 21 and September 23). If we could observe the gnomon’s shadow on those days at sunrise or sunset, then the extension of the line of this shadow would be the local parallel, because the gnomon’s shadow would indicate the east–west direction.
However, it is easy to determine geographical directions with a gnomon on other days too. At the moment when a gnomon casts the shortest shadow, it indicates the north (N). The south is, therefore, the opposite direction (S). 90° to the left of the gnomon is the west (W), and 90° to the right is the east (E).

In the area between the tropics, twice a year, the Sun’s highest point matches the zenith. On the equator, this happens on March 21 and September 23. On the Tropic of Cancer, the Sun appears at the zenith only on June 22, and on the Tropic of Capricorn only on December 22. When the Sun’s highest point matches the zenith, gnomons do not cast a shadow at all.

You should remember that in Poland and in the whole area of the northern hemisphere, except for the intertropical zone, the Sun is always at its highest point on the southern side of the sky. However, in the intertropical zone of both hemispheres, the sun is at its highest point on the northern side in one part of the year, and on the southern side in another. On the rest of the southern hemisphere, the Sun is at its highest point on the northern side of the sky all year, and the shadow cast by gnomons indicates the south.