The Envelope of the Star Gamma Persei
The time between two observable occultations of this variable star is quite long with a period of 29 years. In 2019 it was that time again: An interesting discovery was made in its spectrum at observatories in Canada and Mexico.
At 2.8 mag, Gamma Persei in the northern constellation Perseus is the second brightest eclipse in our sky, but the second eclipse was only observed in November 2019 - this only happens every 29 years. It is also why Gamma Persei's variability went unnoticed until 1990. It lasted for over a week, was 0.3 mag deep in visible light, and was visible to the naked eye. The system consists of two components A and B: a giant star (A) and a smaller companion (B). Nowadays, a digital camera is enough to follow the fluctuating brightness and to create a light curve, and so not only astrophysicists but also amateur astronomers followed the rare spectacle in international cooperation.
At 2.1 mag, the brightest eclipsing star in our sky is Beta Persei, better known by its proper name Algol. In such systems, two stars orbit each other and regularly eclipse each other as seen from our line of sight. Such an eclipsing variable is therefore not a physically variable star such as Delta Cephei or Mira. While most of these "true" variables have well visible light changes, they are at best 3 mag bright or dimmer. However, if smaller changes in luminosity are also taken into account, then even some very bright stars such as Betelgeuse are among the physical variables (see SuW 3/2020, p.24) …
