In astrology, the royal stars of Persia are Aldebaran, Regulus, Antares and Fomalhaut. They were regarded as the guardians of the sky during the time of the Persian Empire (550 BC–330 BC) in the area of modern-day Iran. The Persians believed that the sky was divided into four districts with each district being guarded by one of the four Royal Stars. The stars were believed to hold both good and evil power and the Persians looked upon them for guidance in scientific calculations of the sky, such as the calendar and lunar/solar cycles, and for predictions. The royal stars are mentioned in the Bundahishn, a collection of Zoroastrian cosmogony and cosmology. History The four stars with their modern names, and their ancient Persian names (in brackets) 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/Hastorang) – winter solstice (Watcher of the South) The four dominant stars have an apparent magnitude–1.5 or brighter. and are the brightest stars in their constellations and among the 25–brightest stars in the night sky. In Babylonian and Assyrian times In 747 BCE the Babylonian King Nabu-nasir adopted a calendar derived from the motions of the four stars, one following an eight-year cycle and one a nineteen-year cycle (later adopting the nineteen-year calendar as standard). By 700 BCE the Assyrians had essentially mapped the ecliptic cycle because of the four stars and were in result able to map the constellations, distinguishing them from the planets and the fixed stars. In Persia By the time of the Persian Empire (550 BC–330 BC), Aldebaran watched the Eastern sky and was the dominant star in the Taurus constellation, Regulus watched the North and was the dominant star in the Leo constellation, Antares watched the West and was the alpha star in Scorpio, and Fomalhaut watched the Southern sky and was the brightest star in Piscis Austrinus (sharing the same longitude with the star Sadalmelik which is the predominant star in Aquarius). Aldebaran marked the vernal equinox and Antares marked the autumnal equinox, while Regulus marked the Summer Solstice and Fomalhaut the Winter Solstice. While watching the sky, the dominant star would appear in its season, each having a time of the year when most noticeable. Regulus was seen as the main star because it was in the constellation