Measuring the mass of a single star

In the image at top, left, astronomers discovered a subtle brightening of a star [located within the box] due to the effect of gravitational microlensing. This phenomenon occurs when a foreground star, in this case a dim red star, passes in front of a much more distant star and amplifies its light. Astronomers were engaged in a large-scale search for microlensing events in the halo of our Milky Way galaxy. They were looking in the direction of the Large Magellanic Cloud, a satellite galaxy of our Milky Way. The image was taken in February 1993 with the 50-inch telescope at the Mount Stromlo Observatory in Australia. The box represents the field of view of NASA/ESA Hubble Space Telescope.