The noon or shortest shadow of the Obelisk or shadow clock points due north towards the celestial pole. At the equinoxes (March 21st and September 23rd) the sun rises due east and sets due west, and the observer is at the centre of its semicircular track, called the equinoctial or celestial equator. The angle A which the sun makes with the horizon is called its altitude. The angle Z which it makes with the vertical is its zenith distance. The altitude of the Pole Star is very nearly constant, and on the equinoxes the z.d. of the noon sun is practically equal to the altitude of the Pole Star. Hence the plane of the equinoctial is at right angles to the axis which passes through the observer and the celestial pole. The stars and moon pass over the horizon in circular arcs parallel to that of the sun's transit, rising on the eastern side and setting on the western side of the meridian, or arc, which passes through the north and south points of the horizon, the pole, and the zenith directly overhead.
Diagrammatic view as we might see the sky from the Pyramids today in late summer. The two constellations shown, being very near the pole, do not set below the horizon. Six months later Cassiopeia would be seen sinking after sunset and rising just before sunrise.