Fermi Estimate of the Earth's Size Around the Equator Using Known Distances

Without looking anything up, estimate how far it is around the Earth along the Equator. Explain each assumption and show how you would check that the number is reasonable. ```hint Anchor on something you know Start from a distance you are fairly sure of, then work out what share of a full trip around the planet that distance represents. ``` ### Clarifying Questions - May I use facts I remember, such as how wide a country is or how many time zones it spans, or should the method rely only on what I could observe or measure myself? - How close does the answer need to be: the right order of magnitude, or within roughly 10% of the true figure? - Should the answer be in kilometers or miles? - Can I treat the Earth as a perfect sphere, or should I account for it being slightly wider at the Equator? ### What a Strong Answer Covers - A clear equation that links a known distance to the fraction of a full circle it covers - Inputs labeled as assumptions with round numbers, including a correction when the anchor distance does not lie on the Equator - Arithmetic carried out step by step, without false precision - A sanity check from an independent second method, and which input the result is most sensitive to ### Follow-up Questions - If you could not rely on any remembered facts, how would you measure this with a stick, the Sun and two towns? - Your two methods disagree by 20%. How do you decide which one to trust? - Using your answer, roughly how long would a nonstop flight along the Equator take on a typical airliner?