The horizon and the four angles

The horizon is the line where the sky meets the ground at the birth place. Whatever was above it was visible at the moment of birth, and whatever was below it was not.

The Sun, Moon and planets all travel along one path, the ecliptic. Because Earth turns, that path rises over the eastern horizon and sets in the west once a day. At any moment half of the ecliptic is above the horizon and half is below it.

The Ascendant is the sign and degree of the ecliptic on the eastern horizon at the moment of birth. It is the one point that was rising. It is also called the rising sign.

The Descendant is the opposite point, setting on the western horizon. The two are always exactly 180° apart.

The meridian runs from due north through the point straight overhead to due south. The Midheaven is where the ecliptic crossed it above the horizon. The Imum Coeli is the point opposite, below your feet.

These four points are the four angles. They sweep through the whole zodiac once a day, and they depend on the place as well as the time. The houses are built around them, and in quadrant systems such as Placidus the Ascendant starts the 1st house and the Midheaven starts the 10th.

A chart wheel is a flat drawing of a round sky. The globe below puts the chart back where it came from. The disc is the ground at the birth place, and the colored band is the zodiac along the ecliptic. Each body sits at its height and compass direction for that minute.

Move the time and the whole sky turns while the ground stays still. The Ascendant is whichever degree of the band is crossing the eastern edge of the disc. The Midheaven is where the band crosses the meridian, the dashed arc.