A small-scale gravitational lens effect. In microlensing, the gravitational field of the lensing object is not strong enough to form distinct images of the background source; instead, it causes an apparent brightening of the source. Stars are expected to vary in brightness in a characteristic manner if low-mass stars or planets pass in front of them, and this effect has been detected for stars in the Large Magellanic Cloud and in the central bulge of our Galaxy.