What is gravitational lensing?
The effects of gravity from celestial bodies help to act as a lens, refracting light similar to how
However, generally, the effects of gravitational lensing are only more significantly observed for light coming from distant objects.
Because gravity can affect the path of light (which travels in a straight line due to the law of rectilinear propagation), as light passes around a celestial object with significant gravity, the path of light is bent as it would be when passing through a thin or thick lens.
Depending on the angle and direction by which light passes by the (let's say) cluster of galaxies, light from (let's say) an even further supernova would be refracted by the gravitational effects of the cluster of galaxies that lie between the distant supernova and observation equipment on Earth.
In fact, the above situation was exactly what happened a few years ago in 2015 - where a group of researchers managed to spot images of a supernova being subjected to heavy gravitational lensing, allowing them to observe the supernova from multiple perspectives in the final moments of its life. Here's an image:
Researchers dubbed it as an "Einstein Cross" after Einstein, who had predicted the effects of gravity being able to act as a lens for light.