Gan De
| Gan De | |||||||||||
| Chinese | 甘德 | ||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|
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| Transcriptions | |
|---|---|
| Standard Mandarin | |
| Hanyu Pinyin | Gān Dé |
| Wade–Giles | Kan1 Te2 |
| IPA | [kán tɤ̌] |
Gan De (Chinese: 甘德; fl. 4th century BC) was a Chinese astronomer/astrologer born in the State of Qi also known as the Lord Gan (Gan Gong). Along with Shi Shen, he is believed to be the first in history known by name to compile a star catalogue, preceded by the anonymous authors of the early Babylonian star catalogues and followed by the Greek Hipparchus who is the first known in the Western tradition to have compiled a star catalogue.
Gan De made some of the first detailed observations of Jupiter in recorded history. He described the planet as "very large and bright". In one of his observations on Jupiter, he reported a "small reddish star" next to Jupiter. The historian Xi Zezong has claimed that this was a naked-eye observation of Ganymede in the summer of 365 BC, long before Galileo Galilei's celebrated discovery of the same in 1610 (all four of the brightest moons are technically visible to the unaided eye, but in practice are normally hidden by the glare of Jupiter). By occluding Jupiter itself behind a high tree limb perpendicular to the satellites' orbital plane to prevent the planet's glare from obscuring them, one or more of the Galilean moons might be spotted in favorable conditions. However, Gan De reported the color of the companion as reddish, which is puzzling since the moons are too faint for their color to be perceived with the naked eye. Shi and Gan together made fairly accurate observations of the five major planets.
Shi Shen and Gan De divided the celestial sphere into 365 1⁄4°, as a tropical year has 365 1⁄4 days. At the time, most ancient astronomers adopted the Babylon division where the celestial sphere is divided by 360°.
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