Four points structure the chart: the rising sign in the east, the descendant in the west, the Midheaven at the top, the IC at the bottom.
The rising sign is the sign rising in the east at the moment in question, the Midheaven the one culminating at the highest point.
A chart is drawn for one moment and one place.
The rising sign is the point of the ecliptic that is then on the eastern horizon; its opposite, in the west, is the descendant. The Midheaven is the point of the ecliptic that crosses the meridian, at the highest point of the sky; its opposite, beneath our feet, is the IC. These four points are called the angles.
Calculating them requires the date, the exact time, and the place: from these you get the local sidereal time, then project the horizon onto the ecliptic. A sign takes about two hours to rise, roughly one degree per four-minute slice, with variations by sign and latitude. The birth time therefore weighs heavily in this calculation.
The Midheaven is not always the start of the 10th house. Quadrant systems, including Placidus, do place the cusp of the 10th house there; in Equal houses as in Whole Sign, it can fall in the 9th or 11th house. According to tradition, the rising sign evokes the way of approaching the world, the Midheaven the public direction of a life: these are reading conventions.
Manilius, in the 1st-century Astronomica, describes the four angles of the sky as the strong points of the chart: rising, culmination, setting, and IC. Ptolemy, in the Tetrabiblos, makes the horoscope, the rising degree, the starting point for studying the chart.
The modern formulas for sidereal time and for calculating the angles are those of Jean Meeus, used by the site.
For some, the rising sign is the most important point of a chart and requires a birth time reliable to the minute.
Others prefer the whole sign of the first house, less sensitive to time. The Midheaven is held sometimes to be the cusp of the 10th house, sometimes an independent point. Finally, some astrologers do without the rising sign when the birth time is unknown.
Schools do not all agree: the site sets out the positions without deciding for you, and states the setting it uses by default.
The authors and texts that establish or discuss this concept, with the passage when it is known.
Describes the four angles of the sky (rising, culmination, setting, IC).
The horoscope (the rising degree) as the starting point of the chart.
Sidereal time and coordinates: the basis of the site’s rising sign calculation.
The diagram’s figures are calculated by the site’s engine (Astronomy Engine) or taken from the recorded facts, never copied by hand.
The rising sign is the degree of the ecliptic currently climbing in the east; the Midheaven is the one passing the highest point, in the south in the Northern Hemisphere. They are two different angles of the chart, which tradition does not read the same way.
Because the rising sign gains about one degree every four minutes. A few dozen minutes can change its degree, and two hours can change its sign. The houses depend on it too. Without a time, you can only give a partial chart.
It marks the start of it in the Placidus, Porphyry, and Regiomontanus systems. With Equal houses, or Whole Sign houses, the Midheaven lies elsewhere, sometimes in the 9th or 11th house. It remains the same point of the sky, whatever the system.