--- title: "Meaning & Key Takeaway of: For the observed difference in the shadow…" description: "\"“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 Ea..." image: "https://sms4smile.com/quotes/i/f01/carl-sagan-160_quote_for-the-observed-difference-in-the-shado_681524.jpg" --- # For the observed difference in the shadow lengths, the… ![“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…” quote by Carl Sagan](https://sms4smile.com/quotes/i/f01/carl-sagan-160_quote_for-the-observed-difference-in-the-shado_681524.jpg) [Download](https://sms4smile.com/quotes/i/f01/carl-sagan-160_quote_for-the-observed-difference-in-the-shado_681524.jpg) [Open image](https://sms4smile.com/quotes/i/f01/carl-sagan-160_quote_for-the-observed-difference-in-the-shado_681524.jpg) > ““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.”” [Carl Sagan](https://sms4smile.com/quotes/author/carl-sagan/) ## About This Quote This interpretation was drafted with AI assistance. It is one reading of the quote, not the author's own explanation. 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. ★ ★ ★ ★ ★ No ratings yet [Alexandria Syene](https://sms4smile.com/quotes/about/alexandria-syene-5392498/) [Circumference Earth](https://sms4smile.com/quotes/about/circumference-earth-1843467/) [Distance Alexandria](https://sms4smile.com/quotes/about/distance-alexandria-5392496/) [Earth Intersect](https://sms4smile.com/quotes/about/earth-intersect-5392499/) [Syene Approximately](https://sms4smile.com/quotes/about/syene-approximately-5392497/) ## Related quotes > [Eratosthenes's only tools were sticks, eyes, feet, and brains; plus a zest for experiment. 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