Even the name sounds bad. In Hebrew it’s known as Rōsh ha Sāṭān, in Latin: Caput Larvae. The Chinese know it as dieshi, ‘pile of corpses’. The star system’s modern name, Algol, is derived from ancient Arabic ra’s al-ghūl, literally ‘the ghoul’s head’.
It’s been associated with misfortune, curses, and violence. What could a star do to earn such a horrible reputation? To put it simply, it blinks. Algol the one of the most noticeable variable stars, which means it’s brightness expands and dims in a set rhythm. Imagine what ancient astrologers and astronomers must have felt seeing this thing growing and dying unlike any other star. Few other stars do this and none as visibly as Algol. We think that people knew of this behavior as early as 1,000 BC, probably earlier.
Algol blinks for an interesting reason. Notice at the beginning of the article I used the term star system not star. Algol is actually a set of three stars orbiting around each other in what is known as a trinary star system. They’re just so far away that they appear as a single point of light to anyone without a telescope. One interesting thing about the system is that the axis of rotation is actually perpendicular to our point of view (imagine watching a top spin in front of you at eye level). This arrangement of angles means that occasionally one star will pass in front of another one, eclipsing it’s light and causing Algol to ‘blink’.
In theory the stars should eventually lose momentum and slow down their rotation. And, thanks to the Egyptians, we know that this is actually happening. It takes 2.867 days for the stars to complete an orbit around each other today, but the Egyptians kept such detailed records that we know that around 1200 BC it only took the stars 2.85 days. This means that in the interim three millennia they gained about an extra twenty-four minutes.
Let me just put it this way. We kept such good records that we know down to a matter of seconds how fast a star system ninety-three light years away was spinning three-thousand years ago. Awesome.