Celestial is a slur used to describe Chinese in a derogatory way. Mainly used in the past by whites to describe the Chinese whom they saw as strange and from some where far away. The Chinese used to refer to their nation as the "Celestial Empire"
The word Celestial is a racial slur that has been used historically to degrade and dehumanize chinese. The word is still used by some people for this purpose, and it is seen as offensive and hurtful to chinese. If you are unsure about whether or not it is appropriate to use the word Celestial, it is best to err on the side of caution and avoid using it in any situation.