Decan

The decans are 36 groups of stars used in ancient Egyptian astronomy. These groups helped divide the 360-degree ecliptic into 36 parts of 10 degrees each. This system was useful for keeping time at night. Each decan rose one after another as the Earth turned, marking the start of a new "hour" of the night for the ancient Egyptians.

Because a new decan appeared in the sky every ten days, the Greeks called them dekanói, meaning "tenths." Over time, decans were replaced by a lunar system with 27 or 28 lunar stations. This later evolved into the zodiac with twelve signs. The use of decans can still be seen in the Dendera zodiac, which dates back to around 50 BCE.

Ancient Egyptian origins

Decans were groups of stars used by ancient Egyptians to track time. They appeared on coffin lids during the First Intermediate Period of Egypt and began with the star Sirius, known as "Sothis." Each decan helped mark a part of the night sky, similar to an ancient clock.

There were 36 decans, each covering 10 degrees of the sky, which together made up 360 days of the year. The Book of Nut talks more about these star patterns. These decans helped ancient Egyptians understand the passage of time and the changing seasons.

Later developments

The ancient Egyptians used the predictable appearances of the decans to help organize their calendar. For example, the rising of the star Sirius signaled the yearly flooding of the Nile River.

Over time, these decans were also linked to various ideas in astrology. They were connected to planets like Mercury and Venus, the directions of the compass, and even different qualities like masculine and feminine. These connections were used in ancient astrology to understand many aspects of life.

Descriptions of the decans

Decans are groups of stars used in ancient Egyptian astronomy. They were named in many old books and stories from different places, including Greece and Egypt. Writers like Julius Firmicus Maternus, Cosmas of Maiuma, and Athanasius Kircher talked about them.

Images of these star groups appear in many cultures. An Indian astrologer named Varāhamihira described them, and they even appeared in Japan. The first decan started at a special point in the sky connected to the rising of the star Sirius, which marked the beginning of the Egyptian New Year.

Ancient India

Main article: Drekkana

In ancient India, the zodiac was divided into 36 parts, each spanning ten degrees. This system was known as the drekkana, dreshkana, or drikana. Early mentions of this system appear in works by Sphujidhvaja in Yavanajataka and were later detailed by Varahamihira in his Brihat-Samhita. Scholars think this idea came to India from the Greeks, who had learned it from ancient Egyptian astronomy.