March 2011 page 18
Jos Kint
Stan Ulens

Two Methods to Find the Eccentricity of the Earth’s Orbit from Measurements with a Sundial. Part 2—Observations and Calculations of e

This second part details observations and calculations to determine Earth's orbit eccentricity using a sundial. It applies Ptolemy's geometrical model and an algebraic approach based on the Equation of Time, finding surprisingly accurate results despite the sensitivity of initial conditions.
Equation of Time, How Sundials Work, Mathematics of Dialling

September 2010 page 32
Stan Ulens
Jos Kint

Two Methods to Find the Eccentricity of the Earth’s Orbit From Measurements with a Sundial. Pt. 1: Theoretical Considerations

This article presents two theoretical methods to calculate the Earth's orbital eccentricity using sundial measurements. The first method uses the Ptolemaic geocentric model and season lengths; the second derives eccentricity from the Equation of Time by separating the part due to obliquity from the total.
Equation of Time, How Sundials Work, Mathematics of Dialling