blink microscope, in astronomy, device for determining a change in position or magnitude (brightness) of a star relative to other stars in the background. Two photographs of the same field or area of the sky are projected so that they precisely coincide. The combined image is viewed through a magnifying eyepiece while light from first one photograph and then the other is interrupted mechanically. A change in position or magnitude of a star can usually be detected since the star will seem to flicker or jump to and fro while the background stars remain steady in both position and brightness.