Of or pertaining to the force of gravity; as, gravitational units.

Attractive force of Earth which causes all bodies in her atmosphere to move towards her center.

of or relating to or caused by gravitation

(adj) – Having to do with or caused by gravity

Light cannot escape the pull of gravity; the light from astronomical objects therefore gets deformed - bent, curved or even amplified - if it passes close to a massive body. The massive body causing the effect, a galaxy cluster, for instance, plays the role of a lens. If the lens is spherical then the image appears as an Einstein ring (the image appears as a ring of light), if the lens is elongated then the image is an Einstein cross (it appears split into four distinct images) and if the lens is a galaxy cluster then arcs and arclets of light are formed.