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Gravitational lensing is an amazing and beautiful result from General Relativity. Take a look at the image below.

Light from a distant object is bent by gravity as it travels. Our telescopes therefore see the distant object at a different location from where it actually is. It may also appear brighter or dimmer, depending on whether we receive more or less of the light than normal, and often appears distorted.

A very dramatic gravitational lens is at work in the starfield below. You can see on the right that the blue galaxy's lensed image makes it look as if it were wrapped around one of the bright foreground objects. You can click to see a larger version of the image.

In galaxy lensing, as seen in the image above, the bending of light is so extreme that sometimes the image of the background galaxy is smeared out, or you can see multiple images of the background galaxy.

In microlensing, the physics is the same as that behind the impressive galaxy lensing events, but the effect is much smaller. Still, we can use the presence of gravitational lensing to detect a planet around a star. Because the effect from a single planet is small, this is often called "microlensing".

The trick is that we don't look for a planet creating a lensing effect on its own star. Instead, from our viewpoint, the planet's star must pass in front of another, more distant bright object. This could be another star, a distant galaxy, a quasar, or any other light-emitting object. When the closer star moves in front of the more distant object, there is a gravitational lensing effect caused by the closer star. The planet creates its own lensing effect as well. We can see the difference between lensing from the star, and lensing from a planet and star together. This works even if that planet is not very close to its star, which is an advantage over both the wobble method and the transit method.

Unfortunately, because the stars move slowly across the sky from our viewpoint, this is a fairly rare event, and one that is unlikely to repeat for any given star. Follow-up observations are often impossible. As of this writing, less than two dozen planets have been detected in this manner.

Солнечная система и ее тайны