An error affecting visual estimates of variable stars. It causes a difference in the perceived brightness of a star, relative to another, depending on its position in the field of view. Generally, the star that is either lower in the field or closer to the observer's nose appears relatively brighter. The effect is caused by the variation of sensitivity across the retina, and is independent of variations caused by colour differences such as the Purkinje effect.
Subjects: Astronomy and Astrophysics.