Person: Gan De

Gan De was one of the earliest of the Chinese astronomers.

He was one of the earliest of Chinese astronomers and made observations which he recorded giving dates and coordinates.
We have included Gan De this archive for one reason only.
That is that a quotation from his book Suixing Jing (Treatise on Jupiter) was recorded by later writers.
Apparently, there was a small reddish star appended to its side.
Of course the intriguing question is what was the small reddish star which Gan De saw?
If he did see one of the Galilean satellites, then it would have been Ganymede which is the brightest of the four.
Ganymede can have a magnitude of 4.6 which means that it is within the range which anyone might expect to see.
However the reason that Ganymede is not readily visible is that Jupiter, being so much brighter and so close to Ganymede when viewed from earth, obscures the faint satellite.
Gan De might have possessed exceptional eyesight and been able to separate the faint Ganymede and the bright Jupiter.
The only thing in the description which would have one doubt this is the fact that Gan De records the small star on the side of Jupiter to be reddish.
However, we must remember that he observed under conditions of absolutely no light pollution, something impossible today.
Evidence on the positive side suggesting that he did indeed observe Ganymede comes from the accuracy of his observations in general.
and also gave accurately observed details of the planet's movements throughout its 12 year cycle.
We also know that Gan De produced star catalogues.

Born about 400 BC, China. Died about 340 BC, China.

View full biography at MacTutor

Astronomy, Origin China

Thank you to the contributors under CC BY-SA 4.0!

O’Connor, John J; Robertson, Edmund F: MacTutor History of Mathematics Archive