From the August 2008 issue

Glenn Chaple’s observing basics: See the red star round-up

October 2008: Herschel's Garnet Star and Hind's Crimson Star burn red and brightly this month.
By | Published: August 25, 2008 | Last updated on May 18, 2023
Have you ever been “Purkinjed?” If you’re a variable star observer, you’re susceptible to this phenomenon, called the Purkinje effect, whenever you try to make a visual magnitude estimate of a red star.

Stare at the star directly, and its crimson light excites your retina. As a result, you perceive the star as being brighter than it really is. To avoid being Purkinjed by this color of star, I either quick-glance between it and the nearby field stars I’m comparing it to, or I defocus my telescope to reduce its intensity.