A planetary hour is a concept in astrology and historical astronomy that divides the day and night into twelve parts, each ruled by one of the seven classical planets: Saturn, Jupiter, Mars, the Sun, Venus, Mercury, and the Moon. This system is based on the ancient belief that each planet influences specific hours, affecting various aspects of life. The concept of planetary hours is often used in ritual magic, astrological elections, and other esoteric practices to determine the most auspicious times for specific activities. The division of the day and night into planetary hours is calculated based on the length of daylight and nighttime, ensuring that each planetary hour corresponds to an equal portion of the total time from sunrise to sunset and from sunset to sunrise. In Hebrew, the term is translated as שעת כוכב (sha'at kokhav), while in Latin it is known as hora planetaria. This system has been influential in various cultural and magical traditions, including Hermeticism, Renaissance magic, and ceremonial magic.