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