X
- X PerseiX Persei is a high-mass X-ray binary system located in the constellation Perseus, approxim
- X-ray astronomyBranch of astronomy that uses X-ray observation
- X-ray binaryClass of binary stars
- X-ray pulsarClass of astronomical objects that are X-ray sources
- X-type asteroidGrouping of asteroids
- XO-4XO-4 is a star located approximately 863 light-years away from Earth in the Lynx constella