Occupation: Astronomer and Mathematician
Year born: Around 400 BCE
Research Areas: Jupiter’s movements, Star maps, Sunspots
"[Jupiter] ...was very large and bright. Apparently, there was a small reddish star appended to its side. "
Source: Treatise on Astrology of the Kaiyuan Era, xxiii
There is very little known about Gan De’s life and work, but we do know he was one of the first Chinese astronomers.
Gan De wrote at least 2 books: ‘Treatise on Jupiter’ and ‘Astrological Predictions’. His books have since been lost and are no longer available. We know about his work because later astronomers have made reference to it.
Gan De made accurate observations of Jupiter in sky over several years. One of his observations of Jupiter in 365 BC noted a small reddish star nearby in the sky. It is possible that this was one of Jupiter’s large moons. If it was, Gan De was probably the first person to notice it and must have had very good eyesight. He was doing astronomy long before the invention of the telescope. He Is also one of the first known Chinese astronomers to write a star catalogue.
Gan De also studied the movements of sunspots across the Sun. He described them as ‘eclipses’. Gan De’s observations of sunspots took place over 1000 years before astronomers in Europe did the same.
China are planning a mission to Jupiter. The spacecraft will be called Gan De.