Algol from Gymnome
Algol is an eclipsing binary star which dims regularly as one star goes in front of the other. It's probably the most well known such star, having been known to dim and brighten since the 17th century, or perhaps even since antiquity.
By pure coincidence, Algol is also an eclipsing binary as seen from the slimegirl planet Gymnome.
Yeah! I was playing around with my ZwoNmu system mod for Space Engine, and saw that Algol was a very bright star of 0th magnitude not far from the Oryades (Orion OB1 + Hyades) asterism and the Pleiades cluster. (From Earth it is 2nd magnitude, about the same as Polaris)
Here is a view of the Southern Celestial Sphere of Gymnome, with Algol highlighted. Note to the lower left the incredibly starry 'Oryades' cluster, comprised of the Hyades cluster in front of the much more distant Orion OB1 association, and the Pleiades cluster to the lower right.
Space Engine does not simulate variable stars unfortunately, but I zoomed in on the star and sure enough one star transits the disk of the other star, theoretically dimming it with the same 2.8 day period.
How fascinating that Earth and Gymnome share this property. Essentially this means that the Sun and ZwoNmu are coplanar with the orbit of Algol A & B to a fairly high degree of precision. It also implies that if you draw an arc across Gymnome's sky connecting the Sun to Algol, any stars on that line will also see Algol as an eclipsing binary.
Although, I don't think this has to be incredibly precise because Algol A & B orbit close enough that there is still a fairly wide band of the sky that can be eclipsed.
Betelgeuse also appears to be on that line but I don't have a way of measuring how precise that is and I don't feel like going and checking.
Anyway. The lore implications of this are somewhat interesting. On Earth, there is only weak evidence that ancient astronomers recognized the variability (the strongest evidence is the etymology of its name, referring to a Gorgon in the Greek tradition and a ghoul in the Arabic tradition); it can only be confirmed as early as the 1660s.
But on Gymnome, a 0th magnitude star--one of the very brightest in the sky--suddenly shrinking to 2nd magnitude for 10 hours every 3 days... that would be very strange indeed.
Maybe Algol is a fugitive, shrinking away to hide themself from their pursuers.
Maybe Algol is some kind of great celestial lighthouse.
Maybe Algol is a lesser god, like one of the Oryades stars, only pretending to be as bright and grand as Betelgeuse or Caph, but they have to rest every few nights to regain their energy.
Maybe Algol is, as implied by its earthling nomenclature, a monster of some kind. Maybe Algol's dimming is a bad omen, and people keep almanacs of its brightening and dimming so they can plan decisions and trips and soforth.
On a planet closer to Algol where it would look even brighter, it might even be tempting to design a calendar that accomodates it, but Gymnome's orbit and calendar is weird enough without trying to figure in an Algol-centric set of days of the week. The period of Algol expressed in multiples of Gymnomi sidereal days, is 3.9246. If it was closer to 4.00 I might consider it, but alas.
