Sunsets and solar diameter measurement

TL;DR

This paper explores how sunset observations can be used to measure the solar diameter, comparing it with traditional astrolabe methods and discussing their respective advantages and errors.

Contribution

It introduces a method linking sunset duration to solar diameter measurements and compares it with established astrolabe techniques, highlighting their similarities and differences.

Findings

Sunset duration correlates with solar diameter and azimuth.

Analogies between sunsets and astrolabe observations are established.

Sources of errors in sunset-based measurements are discussed.

Abstract

A sunset over the sea surface offers the possibility to chronometrate a solar transit across the horizon. The vertical solar diameter is proportional to the duration of the sunset, the cosine of the azimuth and the cosine of the latitude of the observing site. The same formula applies to every circle of equal height, called in arabic almucantarat, and it is exploited in the measurements of the solar diameter made with the Danjon's solar astrolabes. The analogies between sunsets and astrolabes observations are presented, showing advantages and sources of errors of these methods of solar astrometry.