Visual Photometry: Colour and Brightness Spacing of Comparison Stars

TL;DR

This paper analyzes the characteristics of visual photometry, revealing consistent estimate dispersion among observers and independence from star colour or brightness spacing, to improve the use of variable star data.

Contribution

It provides an empirical analysis of visual brightness estimates, highlighting their consistent dispersion and independence from comparison star properties.

Findings

Estimate dispersion is 0.2-0.3 magnitudes.

Dispersion is independent of star colour.

Dispersion is independent of brightness spacing.

Abstract

A significant amount of data on the historical and current behaviour of variable stars is derived from visual estimates of brightness using a set of comparison stars. To make optimum use of this invaluable collection one must understand the characteristics of visual photometry, which are significantly different from those of electronic or photographic data. Here I show that the dispersion of estimates among observers is very consistent at between 0.2 and 0.3 magnitudes and, surprisingly, has no apparent dependence on the colour of comparison stars or on their spacing in brightness.