Decan

The decans are 36 groups of stars used in ancient Egyptian astronomy. These groups split the 360-degree ecliptic into 36 parts, each 10 degrees wide. This helped people tell time at night. Each decan appeared one after another as the Earth turned, showing 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." Later, decans were replaced by a system with 27 or 28 lunar stations. This changed into the zodiac with twelve signs. You can still see the use of decans in the Dendera zodiac, which is from 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, called "Sothis." Each decan marked a part of the night sky, like an ancient clock.

There were 36 decans, each covering 10 degrees of the sky. Together, they marked 360 days of the year. The Book of Nut has more information about these star patterns. These decans helped ancient Egyptians understand time and the changing seasons.

Later developments

The ancient Egyptians used the decans to help organize their calendar. The rising of the star Sirius showed when the Nile River would flood each year.

These decans were later linked to ideas in astrology. They were connected to planets like Mercury and Venus, compass directions, and different qualities. People used these connections to understand life in ancient times.

Descriptions of the decans

Decans are groups of stars used in ancient Egyptian astronomy. They were named in old books and stories from places like Greece and Egypt. Writers such as Julius Firmicus Maternus, Cosmas of Maiuma, and Athanasius Kircher wrote 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. This marked the beginning of the Egyptian New Year.

Ancient India

Main article: Drekkana

In ancient India, the zodiac was split into 36 parts. Each part was ten degrees wide. This system was called the drekkana, dreshkana, or drikana. Early talks about this system are in works by Sphujidhvaja in Yavanajataka. Later, Varahamihira wrote about it in his Brihat-Samhita. Scholars think this idea came to India from the Greeks. The Greeks learned it from ancient Egyptian astronomy.