Proof that the Earth is spherical for SS 1

Class: SS 1
Term: First Term
Week: 7
Age: 15 years
Duration: 60 minutes
Subject: Geography
Curriculum Theme: Earth Systems and Environmental
Focal competence: Identify components of the solar system, Earth’s position and motion within it, and how these influence day and night, seasons, and planetary relationships
Key competencies/values: Critical Thinking; Collaboration; ICT and Digital Competencies; Digital Competencies
Skills:

• Identifying and describing the solar system

Previous Lesson: The Earth, Solar System and Planets
Topic: The Earth And The Solar System: Proof That The Earth Is Spherical
Subject Matter: Proof that the Earth is spherical

Specific Objectives

By the end of the lesson, pupils/students should be able to:

Cognitive Domain

• Describe the size and shape of the Earth.
• Discuss the various proofs that the Earth is spherical.

Affective Domain

• Appreciate the scientific evidence supporting the Earth’s spherical shape.
• Collaborate effectively in group discussions about Earth’s shape.

Psychomotor Domain

• Observe and interpret visual evidence of the Earth’s curvature.
• Demonstrate the concept of a curved horizon using a globe and torchlight.

Social Domain

• Participate constructively in discussions about geographical concepts.

Reference Materials

The following resources were used in planning this lesson:

• 2025 New Revised Senior Secondary Education Curriculum (SSEC)
• Relevant State Unified Scheme of Work
• A suitable Geography textbook for SS 1
• The HeadTeacher Scheme of work For The New Revised Senior Secondary Education Curriculum (SSEC)

Instructional Materials

The teacher will teach this lesson with the aid of:

• Video or animation on the solar system
• Photos of Earth from space
• Globe
• Torch light/Flashlight
• Projector (optional, for videos/photos)
• Whiteboard/Chalkboard

Rationale for the Lesson

This lesson is important for students to understand the fundamental shape of our planet, moving beyond common misconceptions. It develops critical thinking by examining observable evidence and reinforces the scientific method through the interpretation of various proofs. This knowledge forms a basis for understanding other geographical concepts like navigation, time zones, and atmospheric phenomena.

Prerequisite/Previous Knowledge

Pupils/students should have a basic understanding of the Earth as a planet and its place in the solar system, perhaps from their Junior Secondary School Geography lessons.

Lesson Content/Board Summary

The Earth And The Solar System: Proof That The Earth Is Spherical

Size and Shape of the Earth

The Earth is an oblate spheroid, meaning it is nearly spherical but slightly flattened at the poles and bulging at the equator. This shape is due to its rotation. While not a perfect sphere, it is often referred to as spherical for simplicity in general terms.

Its approximate equatorial diameter is 12,756 km, and its polar diameter is 12,714 km. The circumference at the equator is about 40,075 km.

Proofs That the Earth is Spherical

Several observable and recorded pieces of evidence confirm that the Earth is spherical. These proofs consistently support the same conclusion:

1. Circumnavigation of the Earth: Explorers like Ferdinand Magellan and Sir Francis Drake sailed continuously in one direction and eventually returned to their starting point. This would only be possible on a spherical or curved surface, not a flat one.
2. The Curved Horizon: When standing on a high point, such as a mountain or a tall building, the horizon appears curved. As one ascends higher, the visible horizon expands and the curvature becomes more noticeable. This is because the Earth’s surface curves away from the observer.
3. Ships Disappearing at Sea: When a ship sails away from the coast, its hull disappears first, followed by its mast. Conversely, when a ship approaches, its mast becomes visible before its hull. If the Earth were flat, the entire ship would simply get smaller and disappear uniformly. This phenomenon is a clear indication of the Earth’s curvature.
4. Earth Imagery from Space: Photographs and videos taken by satellites, astronauts, and space probes clearly show the Earth as a sphere. These direct visual proofs are undeniable and provide the most compelling evidence of its shape.
5. Differences in Visible Stars (Celestial Observation): As one travels from the equator towards the poles, new stars become visible, while others disappear below the horizon. For example, the North Star (Polaris) is visible in the Northern Hemisphere but disappears as one crosses the equator into the Southern Hemisphere, where the Southern Cross constellation becomes visible. This change in the visible celestial sphere is only possible on a curved Earth.
6. Lunar Eclipse: During a lunar eclipse, the Earth passes between the Sun and the Moon, casting a shadow on the Moon. The shadow cast by the Earth on the Moon is always circular. Only a spherical object can consistently cast a circular shadow from any angle.
7. Sunrise and Sunset at Different Times: Different parts of the Earth experience sunrise and sunset at different times. If the Earth were flat, the sun would rise and set simultaneously for everyone on its surface. The progression of day and night across different longitudes is due to the Earth’s spherical shape and its rotation.

Teaching Methods/Instructional Techniques

Discussion, Demonstration, Guided Practice, Question and Answer, Explanation, Observation, Group Work

Instructional Procedures

Step 1: Introduction

Time: 5 minutes

Teaching Skill: Engaging/Questioning

Teacher’s Activity: The teacher greets the students and asks them what they think the shape of the Earth is. The teacher then shows a large photo of Earth from space or a video clip and asks students to describe what they see.

Pupils’ Activity: Pupils respond to the questions and observe the photo/video, describing the Earth’s appearance.

Learning Point: Earth’s perceived shape

Step 2: Discussing Earth’s Size and Shape

Time: 10 minutes

Teaching Skill: Explanation/Discussion

Teacher’s Activity: The teacher guides students to discuss in groups the photo of Earth from space, focusing on its size and shape. The teacher then explains that the Earth is an oblate spheroid, clarifying what that means in simple terms, and provides approximate dimensions.

Pupils’ Activity: Students discuss in groups, then listen to the teacher’s explanation and ask questions for clarification.

Learning Point: Earth’s oblate spheroid shape

Step 3: Proof 1 – The Curved Horizon and Circumnavigation

Time: 10 minutes

Teaching Skill: Demonstration/Explanation

Teacher’s Activity: The teacher uses a globe and a small toy figure to demonstrate how the horizon appears curved from a high point. The teacher also briefly explains the historical circumnavigation of the Earth as proof of its spherical nature.

Pupils’ Activity: Pupils observe the demonstration, ask questions, and relate it to their own experiences of seeing a curved horizon.

Learning Point: Curved horizon, circumnavigation

Step 4: Proof 2 – Ships Disappearing at Sea

Time: 10 minutes

Teaching Skill: Demonstration/Visualisation

Teacher’s Activity: The teacher uses the globe and a small object (e.g., a matchstick representing a ship) to demonstrate how a ship’s hull disappears before its mast as it sails away, and vice-versa. The teacher explains why this happens only on a curved surface.

Pupils’ Activity: Pupils observe the demonstration and discuss how this observation supports the Earth’s spherical shape.

Learning Point: Ships disappearing at sea

Step 5: Proofs 3 & 4 – Earth Imagery and Visible Stars

Time: 10 minutes

Teaching Skill: Visual Aid/Explanation

Teacher’s Activity: The teacher displays more photos of Earth from space, emphasizing the clear spherical shape. The teacher then explains how the visibility of different stars (e.g., North Star vs. Southern Cross) changes as one travels across latitudes, using the globe to illustrate.

Pupils’ Activity: Pupils examine the photos and listen to the explanation, relating it to the concept of a curved Earth.

Learning Point: Space photos, changing stars

Step 6: Other Proofs and Conclusion Reinforcement

Time: 5 minutes

Teaching Skill: Summarisation/Reinforcement

Teacher’s Activity: The teacher briefly introduces other proofs like the Earth’s circular shadow during a lunar eclipse and the different times for sunrise/sunset. The teacher then guides students to summarise how all these observations consistently support the conclusion that the Earth is spherical.

Pupils’ Activity: Pupils listen to the additional proofs and participate in summarising the lesson’s main point.

Learning Point: Consistent spherical evidence

Step 7: Evaluation/Review

Time: 5 minutes

Teaching Skill: Questioning/Assessment

Teacher’s Activity: The teacher evaluates the learning by asking the following questions:

1. Describe the general shape of the Earth.
2. Mention two proofs that the Earth is spherical.
3. Explain why a ship’s hull disappears before its mast when sailing away.
4. How do photos from space confirm the Earth’s shape?

Pupils’ Activity: Pupils answer orally and in writing.

Learning Point: Understanding Earth’s sphericity

Step 8: Note-Taking

Time: 10 minutes

Teaching Skill: Guided Writing

Teacher’s Activity: The teacher guides pupils/students to copy the essential Board Summary notes on the size, shape, and proofs of the Earth’s sphericity into their notebooks.

Pupils’ Activity: Pupils/students copy the notes carefully into their notebooks.

Learning Point: Recording lesson content

Step 9: Conclusion

Time: 5 minutes

Teaching Skill: Consolidation

Teacher’s Activity: The teacher reiterates that the Earth is indeed spherical, supported by numerous scientific observations and historical accounts. The teacher encourages students to continue observing their environment for geographical phenomena.

Pupils’ Activity: Pupils listen attentively and prepare for the next lesson.

Learning Point: Earth’s spherical confirmation

Continuous Assessment/Further Study

Type: Homework/Further Reading

Instruction: Research and write a short paragraph (5-7 sentences) on one additional proof of the Earth’s spherical shape that was not discussed in class. Provide a brief explanation of how it supports the conclusion.

1. Research an additional proof of Earth’s sphericity.
2. Describe the proof clearly.
3. Explain how it demonstrates the Earth’s curved surface.
4. Submit your findings in your Geography notebook next class.

Lesson Keywords

• Spherical – Having the form of a sphere; round.
• Oblate Spheroid – A sphere flattened at the poles and bulging at the equator.
• Horizon – The line where the Earth’s surface and the sky appear to meet.
• Circumnavigation – The action or process of sailing or travelling all the way around something, especially the world.
• Lunar Eclipse – An eclipse in which the moon passes into the Earth’s shadow.

Differentiation

For struggling learners: Provide simplified diagrams and pre-written sentence starters for their discussions. Focus on understanding just two key proofs with clear visual aids. For advanced learners: Challenge them to research the historical context of how people came to accept the Earth’s spherical shape, or to explain the scientific principles behind why the Earth is an oblate spheroid rather than a perfect sphere.

Suggested Lesson Videos

Search on YouTube for: proofs earth is spherical SS1 geography