ephemeris, it was found that the declination of the sun at the instant of observation was
7°58'N. What was the azimuth of the sun?
Calculation Procedures:
- Calculate the azimuth of the body
Refer to Fig. 11. The celestial sphere is an imaginary sphere on the surface of which the
celestial bodies are assumed to be located; this sphere is of infinite radius and has the
earth as its center. The celestial equator, or equinoctial, is the great circle along which the
earth's equatorial plane intersects the celestial sphere. The celestial axis is the prolonga-
tion of the earth's axis of rotation. The celestial poles are the points at which the celestial
axis pierces the celestial sphere. An hour circle, or a meridian, is a great circle that passes
through the celestial poles.
The zenith and nadir of an observer are the points at which the vertical (plumb) line at
the observer's site pierces the celestial sphere, the former being visible and the latter in-
visible to the observer. A vertical circle is a great circle that passes through the observer's
zenith and nadir. The observer's meridian is the meridian that passes through the observ-
er's zenith and nadir; it is both a meridian and a vertical circle.
In Fig. 11, P is the celestial pole, S is the apparent position of a star on the celestial
sphere, and Z is the observer's zenith.
The coordinates of a celestial body relative to the observer are the azimuth, which is
the angular distance from the observer's meridian to the vertical circle through the body
as measured along the observer's horizon in a clockwise direction; and the altitude, which
is the angular distance of the body from the observer's horizon as measured along a verti-
cal circle.
The absolute coordinates of a celestial body are the right ascension, which is the an-
gular distance between the vernal equinox and the hour circle through the body as meas-
SP « polar distance
= 90°-declination
SZ = 90°-altitude
ZP= 90°-latitude
Nadir
FIGURE 11. The celestial sphere.
Zenith
Pole
Vertical
