Astronomy for Astrologers
Horizon Sphere -- A heavenly sphere based on the
plane of the observer's local horizon (90° from both
zenith and nadir), but taken from the center of the Earth.
Zenith -- The zenith is the point directly overhead any
spot on Earth.
Nadir -- The nadir is the point directly beneath (opposite
the zenith) any spot on Earth.
Altitude -- The angular distance of any body above or
below the plane of the local horizon. Altitude is
measured from 0° to 90° from the plane of the horizon
to either pole.
Azimuth -- The angle measured around the 360°
circumference of the horizon, either east or west (there
are different practices). The azimuth of an object is
measured from the meridian plane of the observer and
from a vertical plane through any body.
Prime Vertical – Is a great circle passing through the
zenith (North Pole), nadir (South Pole) and the east and
west points on the horizon.
Altitude Circles -- Parallel circles of altitude, whether
north or south of the plane of the horizon.
Almuncantar -- Parallel circles of altitude, whether north
or south of the plane of the horizon.
North Point – Is a point on the horizon to the north of the
observer, where the meridian plane intersects the
horizon.
South Point – Is a point on the horizon to the south of
the observer, where the meridian plane intersects the
horizon.
East Point -- A point on the horizon to the east of the
observer, where the prime vertical plane intersects the
horizon.