Glossary

Gravitational lensing

Massive objects bend passing light, acting like a cosmic lens that distorts distant images.

Image: NASA, ESA & STScI. Public domain, via Wikimedia Commons (Source)

Because gravity bends the path of light (general relativity), a massive galaxy or cluster between us and a distant source acts as a lens — magnifying, distorting, and sometimes multiplying the background image into arcs or several copies.

The striking “Einstein Cross,” a single quasar lensed into four images, is a famous example, and lensing is now a routine tool of astronomy.

Try it yourself

Stars at the edge of the Sun In 1919 stars shifted in the sky – by about as much as Einstein had predicted, and not by half as much as Newton’s theory implied. On the page: General Relativity tried Eddington’s light table Lay the 1919 eclipse plate over the night plate and measure for yourself how far the stars near the Sun have moved. On the page: General Relativity tried The gravitational lens Move your mouse or finger across the starry sky on the home page: your mass bends the light of the stars behind it. On the home page tried Knowledge quiz: life & physics Questions on Einstein’s life and physics – with an explanation and a source for every answer. On the page: Learn
Source: Wikipedia: Gravitational lensing — Read the full article on Wikipedia.

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