“Einstein’s Telescope” is the latest episode of the New York Times astronomy series Out There. The episode provides a brief explanation of gravitational lensing, which was first theorized by Albert Einstein. As light passes massive objects like galaxies or galaxy clusters, it is bent by that object’s gravity, and–given the right conditions–can provide a view of what’s behind the object.
Recently, astronomers have benefited from gravitational lensing to get four separate views of an exploding supernova more than nine billion light-years from Earth.
