Jupiter is the ruling planet of Sagittarius, and, for many astrologers, also the ruler of Pisces . In Roman mythology Jupiter is the ruler of the gods (having overthrown Saturn) and their guardian and protector, and his symbol is the thunderbolt. In the same way, the planet Jupiter is the king of the other planets, a giant in size with spectacular, brightly coloured clouds and intense storms. Astronomers believe that it plays an important protecting role in using its massive gravity to capture or expel from the solar system many comets and asteroids that would otherwise threaten Earth and the inner planets. Jupiter takes 11.9 years to orbit the sun, spending almost an earth year (361 days) in each sign of the zodiac.

Astrologically Jupiter is associated with the principles of growth, expansion, prosperity and good fortune; and a person's inner sense of justice and morality and their ideals and higher goals. Jupiter governs long distance and foreign travel, higher education, religion and the law. It is also associated with the urge for freedom and exploration, humanitarian and protecting roles, and with gambling and merrymaking or 'joviality'. The first-century poet Manilius described Jupiter as temperate and benign, and the greater benefic. It was regarded as warm and moist in nature, and therefore favourable to life.
The planet Jupiter

In medicine Jupiter is associated with the liver, pituitary gland and the disposition of fats; it governed the blood / sanguine humour. In modern times Jupiter is said to be the ruler of the 9th and 12th houses, but traditionally Jupiter was assigned to the 2nd and 9th houses (the house of values and the house of beliefs, respectively) and had 'joy' in the 11th house of friends and aspirations.

Jupiter is associated with Thursday, and in Romance languages the name for Thursday often comes from Jupiter (for example, jueves in Spanish or jeudi in French). Dante Alighieri associated Jupiter with the liberal art of geometry.

In Chinese astrology, Jupiter is ruled by the element wood, which is warm, generous and co-operative. In Indian astrology, Jupiter is known as Guru or Brihaspati and is known as the 'great teacher'.