The Constellation Perseus The Hero is important in the northern autumn sky. The arrow indicates Algol. Credit: Tony Hallas
Takeaway Keyway:
- Algol (Beta Persei), the second brightest star of Perseus constellation, is a more stars system consisting mainly of two stars, Algol A and Algol B, orbit a common center of Massa in orbit.
- From the terrestrial point of view, algol A and Algol B are periodically eclipsed, causing a significant darkness in the general brightness of the system, observable without telescope.
- The primary eclipse, in which Algol B (a yellowish subgiant) Eclissa Algol A (a blue-white star), causes a decrease in the brightness from magnitude 2.1 to about 3.4, which lasts about 10 hours; This cycle repeats itself approximately every 2.87 days.
- A secondary eclipse, in which Algol A Eclissi Algol B produces a change of not detectable brightness.
In the constellation of Perseus the hero, the star Algol is fun to look due to its regular changes in the brightness. And you don’t even need a telescope. Officially designated Beta Persei, it is the second brightest star of the constellation. What makes Algol particularly interesting is not an intrinsic change in the star itself, but rather a celestial alignment observed by the earth.
Algol is not a single star but a more stars system, mainly consisting of two main components, Algol A and Algol B, which orbit a common mass center. A third more single star, Algol C, also orbit to this couple, but does not affect what we see. The fascinating aspect of Algol A and Algol B is their close closeness and orientation of their orbit with respect to the earth. From our point of view, these two stars are periodically eclipsed.
The primary star, Algol A, is a warm and blue-blue star, while Algol B is a larger yellowish subgiant, cooler and less bright. When Algol B passes in front of the brighter algol, it blocks a significant part of its light. Astronomes call this event the primary eclipse. During this period, the combined brightness of the Algol system, normally around size 2.1, temporarily drops to a minimum brightness of about the size 3.4. This darkness is evident to the eye without help.
This cycle of eclipse is significantly coherent, which occurs about 2 days, 20 hours and 49 minutes or 2.87 days. The entire recall and relegation process lasts about 10 hours. There is also a secondary eclipse, which happens when the brightest algol passes in front of the most unbridled algolo B. However, this secondary eclipse causes only a slight dip in the brightness that we cannot even detect through telescopes.
Historical observations suggest that algol variability could have been noticed by the ancient astronomers, who could influence its traditional name, which has roots in Arabic and means “the head of the demon” or “the ghoul”. This is probably attributed to his dampening behavior, which would seem unusual and perhaps mysterious to the first Skywatchers. Modern astronomy, however, provides a clear and predictable explanation for this intriguing stellar phenomenon.
Then, go out early and identify Algol. So watch it for several nights in a row and you will also see it change in brightness. Not only that, but now you will know why.
