Section 1: Proof That the Earth Is a Sphere
Observation:
Imagine standing on a beach watching a ship sail away toward the horizon.
Question 1:
What do you notice about how the ship disappears as it moves away?
Feedback:
If the student answers: “The bottom disappears first,” or mentions “hull,” “curve,” or “curved Earth,” respond:
Correct! The bottom vanishes first because the Earth is curved. If the Earth were flat, the whole ship would shrink evenly.
Otherwise:
Look again! Does the ship disappear evenly, or does something vanish first? Try to describe it.
Observation:
During a lunar eclipse, the Earth’s shadow falls on the Moon.
Question 2:
What shape is the Earth’s shadow on the Moon during an eclipse?
Feedback:
If the student answers: “Round,” “circle,” “always round,” respond:
Exactly! Only a sphere always casts a round shadow, no matter what angle the light hits it.
Otherwise:
The shadow is always round, like a perfect circle. What shape would always cast a round shadow?
Quick Quiz:
Why can’t you see the same stars in Colombia as at the North Pole?
Why does the Sun get higher in the sky as you travel south from Europe to Africa?
Feedback:
Because the Earth is curved—a different part of the sky is visible depending on where you are on the sphere
Section 2 Why the circle has 360 degrees
I choose a clear spot—perhaps a hill or a temple courtyard—where I have a wide, unobstructed view of the eastern and western horizons
Marking the Sunrise and Sunset
- Each day at sunrise, I stand in the same place and note exactly where the Sun rises on the horizon.
- I place a small stone or carve a mark on a wall to record the Sun’s position.
Watching the Shifting Points
- As days pass, I notice the Sun doesn’t rise in the same spot every day.
- After the summer solstice, the sunrise point shifts southward along the horizon, day by day.
- After the winter solstice, the sunrise point moves back northward.
The Cycle Closes
- Over many months, I keep adding marks.
- After nearly 365 sunrises, I see the Sun rises again in the same spot as it did exactly one year ago—lining up with my original mark.
- The pattern repeats: solstice, equinox, solstice, equinox… always coming back to my marked spots
Summary in Ancient Words
“By watching where the Sun rises and sets each day, and by marking those spots, I see that after a full cycle of seasons—after one year—the Sun comes back to the same place on the horizon. The days, nights, and seasons repeat in the same order. The Sun’s path is a great circle, repeating endlessly, proof of the year’s cycle.”
Ancient astronomers linked the length of the year to geometry. Because the Sun seemed to complete its circle in the sky after about 360 days, they divided both the year and the circle into 360 parts. That’s why a full circle is 360 degrees: each degree once represented a day in the Sun’s journey through the year.
Fixed Observer’s View of the Sun’s Noon Arc Through the Year
- June 21 (Summer Solstice):
Sun follows its highest arc in the sky . - September 21 (Autumn Equinox):
Sun follows a midway arc (lower than June, higher than December) - December 21 (Winter Solstice):
Sun follows its lowest arc - March 21 (Spring Equinox):
Sun again follows the midway arc (, same as September. - Next June 21:
Sun returns to the highest arc
Section 3: The Eratosthenes Experiment
[Teacher:]
Let me take you back to ancient Egypt, over 2,000 years ago. Imagine you’re Eratosthenes, the head librarian in the city of Alexandria—a city full of scholars, scrolls, and big ideas.
[Slide/Visual: Map of Egypt, showing Syene and Alexandria]
[Teacher:]
One day, you hear an interesting fact:
On the summer solstice, at noon in the city of Syene (now called Aswan), the Sun is directly overhead. So much so that it shines straight down a well—no shadow at all!
But, in Alexandria, far to the north, you notice that at the same date and time, a stick does cast a shadow.
[Teacher holds up a stick or pointer.]
Let’s try to visualize what this means.
If the Earth were flat, what would you expect to happen to the shadow in Alexandria when the Sun is overhead in Syene?
(Let students answer: “No shadow!”)
But Eratosthenes saw a shadow! That’s our first clue that the Earth is curved.
[Slide/Visual: Diagram showing vertical stick in Syene (no shadow) and in Alexandria (with shadow)]
You, Eratosthenes, decide to measure the angle of the shadow in Alexandria at noon on the solstice.
It turns out to be about 7.2 degrees.
What is the measure of the central angle xyz? Hint think of aline intersecting 2 parallel lines
[Teacher draws or shows angle on board or slide.]
Now you remember:
- The distance between Syene and Alexandria is about 5,000 stadia .
If one stadium is approximately 160 meters how many kilometers in 5000 stadia?
Hint :convert 5000 stadia to meters and meters to kilometers. - If 7.2 degrees represent so many kilometers, then 36o degrees represent how many k,. HintÑ use proportion. This 360 degrees converted to k, represent the circumference of the earth.
Answer at the end of the lesson. Resist tentation to look oo quicikly at the answer
(Let students respond; then guide them if needed.)
Once you find the circumference, can you determine the diameter and the radius?
HintÑ given the formula circumference equal 2*3.14*radius, express radius in terms of circumference
once you have the radius, it is a simple matter of multiplying rqdius by 2 to get diameter
Section 4: Observable Components of the Earth
As we explore our planet, we can identify three main layers of study:
🌊 Oceans – Descend below 100 km and you’ll encounter a vast blue expanse covering most of Earth’s surface. This is the domain of Oceanography where we study the interconnected bodies of water that shape climate, life, and weather.
🌍 Landmasses – Rising above the water, you’ll see continents and islands in a mosaic of colors. This is the combined domain of Geologyand Geography
Geography examines the patterns of human and natural landscapes, while Geology focuses on the Earth’s structure, rocks, and the processes that have shaped them over time.
☁️ Atmosphere – Finally, lift your eyes above the surface and you’ll notice a light blue haze surrounding our planet. This is the Atmospheric Studies, the realm of Meteorology and atmospheric science, where we study weather, climate, and the gases that make life possible.