# A measurement of the ecliptic’s obliquity is later credited to Eratosthenes as a distinct astronomical heading

Date: 240

## The fact

Britannica states that he measured the degree of obliquity of the ecliptic; MacTutor treats the same heading among the lost astronomical writings.

It is one event.

## Context

This is not the Syene well story. Do not invent a unique modern arcsecond residual as his number.

[Eratosthenes](/people/eratosthenes)’s documented role is bounded by other offices and collaborators named in the sources below. Sharing a field with them is not a reason to drop a documented act, and it is not a reason to assign later consequences done in the name after death.

Conventional years are c.276–c.194 BCE. Almost no autograph survives. Cleomedes, Strabo, Nicomachus, and later encyclopedias are the public file. Classroom globe reconstructions are not his acts. Contribution is complex.

Named person as heading of the dated public instrument. Later editors, museums, printers, or offices share publication. Complex where later carriers are the surviving public file.

## Evidence and sources

Britannica and MacTutor independently name an obliquity measurement under his heading.

Official or archival record: Britannica — Eratosthenes (https://www.britannica.com/biography/Eratosthenes; Encyclopaedia Britannica).

## Significance

A later-credited tilt measurement is a knowledge-access path for calendrical and geographical work. It is not a satellite series.

## What is established and what is not

Established: later scientific lives credit him with an obliquity figure. Not established: the observing log or that a modern textbook conversion is the autograph fraction.

What would change the picture: a contradictory original with a different date or name, or a measured series that can be argued, with lag and alternatives, as a consequence of this instrument rather than of later institutions.

The date is the date of this instrument, not a licence to back-date every later harm or benefit.

Established here: a sourced, dated public instrument with a named contribution by Eratosthenes.

They are not a public rating.

Eratosthenes did not file a later UNESCO form, a later Loeb colophon, or a later museum label as a personal act. A portrait or conventional bust is not this mechanism. Allegation, reconstruction, and established occurrence stay distinct. Split from the circumference row. Do not use a planetarium show as the date field. Keep the carrier date of later English distinct from the received historical year stored in the date field. Do not read a later English edition as a recovered autograph of Eratosthenes.

## People

- Eratosthenes: https://factrail.ai/people/eratosthenes

## Drivers

- Digital Learning Access: https://factrail.ai/drivers/edu-digital-learning-access

## Sources

- https://www.britannica.com/biography/Eratosthenes
- https://mathshistory.st-andrews.ac.uk/Biographies/Eratosthenes/

## Methodology

https://factrail.ai/methodology

Canonical: https://factrail.ai/facts/era-obliquity-ecliptic