Here are some synonyms for "celestial", depending on the specific context:

General:

* Heavenly

* Cosmic

* Astronomical

* Starry

* Extraterrestrial

* Supernal

* Empyrean

* Ethereal

More specific:

* For objects: Lunar, solar, stellar, planetary

* For events: Astral, sidereal

* For beauty: Divine, sublime, glorious

The best synonym will depend on the specific meaning you want to convey.