Circumference Earth Quote by Carl Sagan
““For the observed difference in the shadow lengths, the distance between Alexandria and Syene had to be about seven degrees along the surface of the Earth; that is, if you imagine the sticks extending down to the center of the Earth, they would there intersect at an angle of seven degrees. Seven degrees is something like one-fiftieth of three hundred and sixty degrees, the full circumference of the Earth. Eratosthenes knew that the distance between Alexandria and Syene was approximately 800 kilometers, because he hired a man to pace it out. Eight hundred kilometers times 50 is 40,000 kilometers: so that must be the circumference of the Earth.””
About This Quote
Source Book: Cosmos, Carl Sagan, 1980
Eratosthenes measured Earth’s size by comparing shadows, using geometry and known distances to estimate circumference.
In simple terms: He used shadow angles and distance to calculate Earth’s size.
Key Takeaway
Apply simple geometry to estimate large scales.
Themes
science
measurement
geometry
history
curiosity
Mood
inquisitive
reflective
Type
educational
historical
When to use this quote
- educational lectures
- science museums
- classroom demonstrations
- DIY experiments
Key Concepts
ancient astronomy
trigonometry
empirical method
Questions to Reflect On
- How can we verify ancient measurements today?
- What modern methods improve on this approach?
A Different Perspective
Assumes accurate distance measurement and uniform Earth shape; modern tools give more precise data.
![“[ When a religious couple wrote to Sagan about fulfilled prophecies, he wrote back in May 1996 :] If ‘fulfilled prophecy’ is your criterion, why do you not believe in materialistic science, which has an unparalleled record of fulfilled prophecy? Consider, for example, eclipses.” quote by Carl Sagan](https://sms4smile.com/quotes/img-quotes/875/carl-sagan-160_belief_when-a-religious-couple-wrote-to-sagan-a_25095.jpg)
