The four Royal stars or Guardians of the Sky were a group of stars noticed by the Persian astrologers, and mentioned by Zarathustra[1] , around 3000 BC and used as a rudimentary season calendar.
All four stars are among the brightest 25 stars, having an apparent magnitude of less than 1.5. However, this particular set of stars was chosen because they are divided on the sky by approximately 6 hours apart in right ascension. The reason why they are called "royal" is that they appear to stand aside from the other stars in the sky. Throughout a year, each star is for several months "dominant" on the night sky and one can guess the season just by noticing which star is dominant.
The position of "Watcher" for Venant and Haftorang has caused confusion. Persian astrologists associated Venant (Regulus) with the North, and Haftorang/Hastorang (Fomalhaut) with the South due to their stellar positions.[2] Some contemporary astrologists and Neopagans have flipped these positions due to their seasonal/directional associations.[3]
The four stars with their modern and ancient Persian names were: