The same process is done for houses two and three. This timeline, called a diurnal arc, is divided into equal thirds. Instead of dividing the space between the midheaven to find where houses eleven and twelve begin, however, the time it takes for the sun to move from it's rising position to its noontime position is calculated. The ascendant, midheaven, descendent, and IC are all found the same way and, similar to Porphyry, the rising sign also begins the first house while the midheaven begins the tenth house. Placidus houses will look a lot like Porphyry houses. Because it is a time based house system, you could simply make a table for how a house cusp changes across time zones, making this method popular among journalists. This is because Placidus houses can be calculated across time zones without a calculator. The most popular house system in use today is Placidus. The descendent and IC are found by finding the points 180 degrees from the ascendant and midheaven, respectively, and the space between the ascendent and IC is again divided into three houses. The space between the ascendent and the midheaven is then divided evenly into equal thirds. In the Porphyry house system, which is a space based house system, the ascendant starts the first house and the midheaven starts the tenth house. The descendent, again, 180 degrees from the ascendent and the IC is 180 degrees away from the midheaven. In this house system, your midheaven can still be located anywhere above the horizon of your chart. If your rising sign is at 20 degree Aries, then your second house would start at 20 degrees Taurus, your third house at 20 degrees Gemini, and so on.

Each house is exactly 30 degrees, meaning each house starts in a different sign at the degree of your rising sign. In the equal house system, your ascendant starts off your first house. The descendent is 180 degrees away from the ascendent and the IC is 180 degrees from the midheaven. The ascendant is anywhere in the first house and the midheaven can be located anywhere above the horizon (anywhere between houses seven and twelve). In the whole sign house system, every house is an entire sign beginning with whatever sign the ascendant is in. This is because they are the easiest to use. The oldest, and most popular throughout history, house systems have been ecliptic based.

We will look at two types of ecliptic based houses systems, whole sign and equal, one spatial, Porphyry, and one temporal, Placidus.

There are three different types of houses systems: ecliptic, spatial, and temporal.

Astrology house calculator