A Brief Astrology History- The Foundations of Western Astrology

Hellenistic Astrology established the four fundamental pillars of Western astrology: the planets, the twelve zodiac signs, the twelve houses, and the major aspects between planets.

During this period, astrologers observed how planets moved along the zodiac and combined this with the Egyptian concept of the 36 decans, where each zodiac sign corresponds to three decans. They also paid close attention to how planets rose over the eastern horizon and set in the west throughout the day.

The decan rising on the eastern horizon at the time of birth was considered especially significant. This concept evolved into what we now know as the Ascendant sign.

The Ascendant sign was designated as the first house, followed counterclockwise by the second through twelfth houses. This equal division of the houses became known as the Whole Sign House System.

The concept of rulership, along with its diagram, the Thema Mundi (link), also originated in this period.

The Moon, being the closest celestial body to Earth and orbiting it directly, was considered the first and most personal luminary, ruling Cancer. The Sun was assigned rulership of Leo, because when the Sun reaches 15° Leo, it marks the height of summer in the northern hemisphere—when the Sun stands highest and strongest in the sky.

I personally don’t fully grasp the exact logical sequence behind these assignments, but clearly, the ancients saw patterns and categorized them this way.

In the Thema Mundi, planetary rulerships were determined based on each planet’s distance from the Sun and its orbital speed, using Leo as the central reference point.

• Mercury, which never strays more than one sign from the Sun (unless retrograde), was assigned to Virgo. For example, if your Sun is in Leo, your Mercury will either be in Cancer, Leo, or Virgo.

• Venus, which moves no more than two signs away from the Sun (unless retrograde), was assigned to Libra.

• By extension, Mars was assigned to Scorpio, Jupiter to Sagittarius, and finally, Saturn to Capricorn.

These rulerships were then mirrored from Cancer to the remaining five signs, creating the full rulership scheme.

From the starting point of the Sun and Moon in Leo and Cancer, planets forming 60° (Venus) and 120° (Jupiter) aspects were considered harmonious and beneficial. In contrast, planets forming 90° and 180° aspects (Mars and Saturn) were seen as challenging and difficult.

Angles themselves are fascinating. For instance, people with more angular facial structures tend to appear determined and resilient, whereas those with softer, rounder features often seem more approachable and diplomatic. I often think of this parallel when interpreting planetary aspects.