The horizon was extremely important to the Egyptians, since it was here that the Sun appeared and disappeared daily. A hymn to the Sun god Ra shows this reverence: 'O Ra! In thine egg, radiant in thy disk, shining forth from the horizon, swimming over the steel firmament.' The Sun itself was represented by several gods, depending on its position. A rising morning Sun was Horus, the divine child of Osiris and Isis. The noon Sun was Ra because of its incredible strength. The evening Sun became Atum, the creator god who lifted pharoahs from their tombs to the stars. The red color of the Sun at sunset was considered to be the blood from the Sun god as he died. After the Sun had set, it became Osiris, god of death and rebirth. In this way, night was associated with death and day with life or rebirth. This reflects the typical Egyptian idea of immortality.

Astronomy for Practical Uses

The center of Egyptian civilization was the Nile River, which flooded every year at the same time and provided rich soil for agriculture. The Egyptian astronomers, who were actually priests, recognized that the flooding always occurred at the summer solstice, which was also when the bright star Sirius rose before the Sun. The priests were therefore able to predict the annual flooding, which made them quite powerful.

Many Egyptian buildings were built with an astronomical orientation. The temples and pyramids were constructed in relation to the stars, zodiac, and constellations. In different cities, the buildings had different orientations based on the specific religion of that place. For instance, some temples were constructed to align with a star that either rose or set at harvest or sowing time. Others were oriented toward the solstices or equinoxes. As early as 4000 B.C., temples were built so that sunlight entered a room at only one precise time of the year.

An alternative building method was to gradually narrow successive doors into a specific room, in order to concentrate the sunbeams onto a god's image on the wall. The designs sometimes became quite complex. At the temple of Medinet Habu, there are actually two buildings which are slightly off-kilter. It has been suggested that the second one was built when the altitude of the other temple's orientation stars changed over a long period of time. The picture below shows Medinet Habu and the relative orientation of its temples.

http://physics.unr.edu/grad/welser/astro/egyptian.html