Royal stars
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The four Royal stars or Guardians of the Sky were a group of stars noticed by the Persian astrologers 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 four stars with their modern and ancient Persian names were:
- Aldebaran (Tascheter) - vernal equinox (Watcher of the East)
- Regulus (Venant) - summer solstice (Watcher of the North)
- Antares (Satevis) - autumnal equinox (Watcher of the West)
- Fomalhaut (Haftorang) - winter solstice (Watcher of the South)
