For 10 points, identify this astronomical event where, unlike strong and weak lensing, the mass of the lens is only about the size of a star.
The filtering out of so-called "blue bumpers" is important when searching for this. The AGAPE project and the Angstrom project concern discovering these phenomena in the Andromeda galaxy, and this phenomenon was first named by Paczynski in a paper that also inspired the OGLE and DUO projects that were the first to search for this. It has been used to detect certain dark matter candidates in the galactic halo and in the Large Magellanic Cloud via the MACHO experiment, but it may be better known for its capacity to detect low-mass extrasolar planets. For 10 points, identify this astronomical event where, unlike strong and weak lensing, the mass of the lens is only about the size of a star.
The filtering out of so-called "blue bumpers" is important when searching for this.
gravitational microlensing [prompt on gravitational lensing]