Astrology

Astrology (占星術) is a system involving the use of astrological phenomena, such as the positions of the stars and planets in the night sky, for the purpose of divination.

In Toaru Majutsu no Index, certain forms of Magic make use of astrology.

Etymology
Astrology is derived from the Latin astrologia, in turn derived from the Greek ἀστρολογία, approximately meaning 'study of the stars', comprised of ἄστρον/astron ("star") and -λογία/-logia, ("study/account of"). Astrologia later came to refer to 'star-divination' while astronomia (later ) was used for the scientific term.

Principles
There are various patterns formed by the stars in the night sky, and some of these are considered to form images at specific points in the night sky. These are known as constellations (星座). The number of recognized constellations have changed over time and between different locations, with many cultures having various tales associated with them. In modern times, there are eighty-eight officially recognized constellations, many of them derived from Classical Mythology.

Among these are a group of twelve constellations known as the, which follow the ecliptic belt across the celestial sphere which the Sun and planets travel along. The signs of the Zodiac are important elements in astrology, with various attributes associated with them, such as personality types, elements, times of the year and day, and ruling planets.

The planets are another important aspect of astrology, with the ones traditionally used being Mercury (水星), Venus (金星), Mars (火星), Jupiter (木星) and Saturn (土星), together with the two 'lights'; the Sun (太陽) and the Moon (月). Like the Zodiac signs, the planets have various qualities associated with them.

The positions of the constellations and the planets observed in the night sky and in relation to each other (angles and proximity), combined with their individual qualities, are used to divine for a specific point in time, with different meanings and interpretations arising at different times. These positions and meanings can be used as a basis for various spells, a fair number of which are dependent on the state of celestial sphere.

Western Astrology
In Western Astrology, the twelve signs of the Zodiac are Aries (おひつじ座), Taurus (牡牛座), Gemini (双子座), Cancer (蟹座), Leo (獅子座), Virgo (乙女座), Libra (天秤座), Scorpio (蠍座), Sagittarius (射手座), Capricorn (山羊座), Aquarius (水瓶座) and Pisces (魚座). As well as a month-long time period in the year, personality type and element, they also have one of three modalities:, and.

Astrology of this kind plays an important role in Hermeticism, being said to be one of the three parts of the wisdom of the universe held by Hermes Trismegistus.

Eastern Astrology
Onmyoudou makes use of certain aspects of astrology.

Indian astrology, also referred to as Vedic and Navagraha Astrology (九曜占星術), tells fortunes through the positions of 9 Navagraha; the Sun, the Moon, Mercury, Venus, Mars, Jupiter, Saturn, Rāfu (ラーフ) and Kēto~u (ケートゥ), as well as the angles of the constellations.

Deep Blood Arc
Index mentioned astrology during her first meeting with Himegami Aisa regarding her validity as a magician. Modern Astrology was included in her list together with the likes of Enoch Kabbalah, Hermeticism and Vision of Mercury.

Daihasei Festival Arc
Astrology is referred to during the events in the Daihaseisai, with some of the laws behind Oriana Thomson's Shorthand coming from the basis of Western Astrology.

Toaru Majutsu no Index SS: Necessarius Special Admission Test
Astrology is referred to among the various magical-related systems which depend on the positions of the stars in the night sky, which the group known as the Royal Astronomical Research Organization was formed to observe, in order to obtain data regarding the use of those systems.

Uses of Astrology within the story

 * Oriana Thomson makes use of the laws which form the basis of Western Astrology, concerning the relationships between the planets and constellations at different angles, as part of her Shorthand technique.
 * Etzali's obsidian dagger Spear of Tlahuizcalpantecuhtli (トラウィスカルパンテクウトリの槍) requires the light of Venus as part of Idol Theory to reflective off it to disassemble targets.
 * Sozty Exica makes use of Navagraha Astrology when reading Kamijou Touma's fortune.

Astrological organizations

 * Astrological Surgery Brigade
 * Royal Astronomical Research Organization