Eratosthenes
Life
An Alexandrian scholar remembered for turning two shadows into a calculation of Earth’s size. His own account is lost; the later writer Cleomedes describes a method using the difference in solar altitude at Syene and Alexandria and an estimated distance between them. The result is reported as 250,000 or 252,000 stadia, but uncertainty about the stadion and the geographical assumptions prevents a single trustworthy modern error percentage. The geometric idea remains elegant and reproducible. The sieve bearing his name, along with his work on chronology and geography, shows a much wider range. The nickname Beta and the story that he fasted after losing his sight belong to later tradition.
Decisive moments
Linking an angle and a distance to Earth’s circumference
AlexandriaA later account says he used the difference in solar altitude at Syene and Alexandria together with the estimated distance between them. The method is powerful, but uncertain inputs and units make the modern error percentage interpretation-dependent.
Sieve of Eratosthenes
Starting at 2, cross out multiples of each surviving prime. It is a hand-worked puzzle for beginners and leads to segmented sieves and complexity analysis at advanced levels.
Later traditions about his death
A tradition says that after losing his sight in old age he ended his life by fasting, but it is not supported by the same kind of direct evidence as his mathematical work.
If this person hadn't existed
This is a thought experiment about influence, not a verified historical fact.
Beginners compare two shadows with a lamp and sticks; intermediate learners turn the angle into a fraction of a circle. Advanced learners model errors from a non-spherical Earth and cities that are not exactly on one meridian. Experts compare Cleomedes’s account, possible stadion lengths, and route estimates to see why converting an ancient result into one modern accuracy claim is difficult.
Beyond MathVoyage
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