Etymology

Etymology

The Sanskrit term for horo is hora (होरा). Horo-scope is hora-shastra (होरा-शास्त्र). The Latin word horoscopus, ultimately from Greek ὡρόσκοπος "nativity, horoscope", literally "observer of the hour [of birth]", from ὥρα "time, hour" and σκόπος "observer, watcher". In Middle English texts from the 11th century, the word appears in the Latin form and is anglicized to horoscope in Early Modern English. The noun horoscopy for "casting of horoscopes" has been in use since the 17th century (OED). In Greek, ὡρόσκοπος in the sense of "ascendant" and ὡροσκοπία "observation of the ascendant" is in use since Ptolemy (Tetrabiblos 33, 75).

Concepts in Western astrology

• The native is the subject of the event (a birth, for example) being charted at a particular time and place, and is considered to be at the centre of the celestial sphere.

• The celestial sphere is an imaginary sphere onto which the zodiac, constellations and planets are projected.

• The plane of the equator is the plane of the Earth's equator projected into space.

• The plane of the ecliptic is defined by the orbits of the earth and the sun. For practical purposes the plane of the equator and the plane of the ecliptic maintain a constant inclination to each other of approximately 23.5°.

• The plane of the horizon is centred on the native, and is tangential to the earth at that point. In a sphere whose radius is infinitely large, this plane may be treated as nearly equivalent to the parallel plane with its centre at the Earth's center. This greatly simplifies the geometry of the horoscope, but does not take into account that the native is in motion. Some writers on astrology have thus considered the effects of parallax, but most would agree that (apart from that of the moon) they are relatively minor.

Angles

There are four primary angles in the horoscope. These are, in order of power:

• First House (Ascendant – East Angle)

• Tenth House (Midheaven or M.C. – North Angle)

• Seventh House (Descendant – West Angle)

• Fourth House (Imum Coeli or I.C. – South Angle)

The ascendant is the easternmost or sunrise point where the ecliptic and horizon intersect; the ascendant and the midheaven are considered the most important angles in the horoscope by the vast majority of astrologers. In most systems of house division, the ascendant is the cusp of the 1st house and the midheaven is the cusp of the 10th house. The placement of the planetary ruler of the ascendant, called the chart ruler is also considered to be significant. The point in the west diametrically opposing the ascendant is called the descendant, normally the cusp of the 7th house; and the point opposing the M.C. is the cusp of the 4th house, the northernmost point of the chart, called the imum coeli or I.C.

In creating a horoscope the ascendant is traditionally placed at the "nine o'clock" position on the left-hand side of the chart wheel (though traditional rectangular chart formats need not follow this convention). During the course of a day, because of the Earth's rotation, the entire circle of the ecliptic will pass through the ascendant and will be advanced by about 1°. This movement provides us with the term rising sign, which is the sign of the zodiac rising over the eastern horizon at the moment of birth. The point on the ecliptic that is furthest above the plane of the horizon at the time is called the Midheaven, or medium coeli (M.C.), placed at the "twelve o'clock position" effectively where the Sun would be if the birth time was midday.