Every 2 hours or so, a new sign of the Zodiac is busy by ASC and, similarly, the other points (DISC, MC, IC). During this rotation the horizon is continually crossed by two points representing the lifting and the lowering of the Sun The ASC indicates precisely, for a given day at a given place, the sunrise, the sunset and the DISC. Among them are placed in the highest point of the meridian, noon (MC), and the lowest point midnight (IC). These positions correspond to the cardinal points of a paper astronomical, which are reversed compared to those of a map of the Earth. Those born at dawn will the Sun near the Ascendant, those born at noon will be close to the Sun MC, those born at sunset will have it next to the DISC and those born at midnight will have it close to the IC. The intermediate spaces between the four points correspond to other times of day.
As well as the line ASC-DISC divides the zodiac into two semicircles, one upper and one lower, also the line MC-IC divides it into two equal semicircles, one right and one left of the meridian.
In the past, the design of the horoscope has assumed different geometric shapes, including square. The latter follows from the definition of the ancient "four quadrants" to indicate what are now the four semicircles. The distribution of the planets in semicircles has special meanings.