A system for tracking an orientation of a first object, the system comprising: a light emitting device located relative to a second object at a fixed predetermined position; a sensor having a square two-by-two photodetector array that is configured to receive incident light emitted from the light emitting device, the square two-by-two photodetector array being mounted on the first object; and a processor coupled to the square two-by-two photodetector array, the processor configured to determine the orientation of the first object relative to the second object based on an angle of incident light detected by the square two-by-two photodetector array from the light emitting device, wherein the sensor includes: a housing having a first side and a second side, the second side being opposite to the first side and spaced therefrom, the square two-by-two photodetector array being located proximal to the second side within the housing; and an aperture extending through the first side of the housing and configured to expose the four photodetectors (18a-d) of the square two-by-two photodetector array to an incident light from the light emitting device, wherein each of the four photodetectors (18a-d) is square shaped, and wherein the aperture has the same square shape and dimensions as each photodetector, and wherein the aperture is spaced from the square two-by-two photodetector array by a distance equal to a width or length of the square shape of each photodetector; and wherein the processor is configured to detect an angle of incidence of a light source based on light intensity readings detected at one or more regions of a light-receiving surface of the square two-by-two photodetector array that are illuminated by light entering the sensor through the aperture. a light emitting device located relative to a second object at a fixed predetermined position; a sensor having a square two-by-two photodetector array that is configured to receive incident light emitted from the light emitting device, the square two-by-two photodetector array being mounted on the first object; and a processor coupled to the square two-by-two photodetector array, the processor configured to determine the orientation of the first object relative to the second object based on an angle of incident light detected by the square two-by-two photodetector array from the light emitting device, wherein the sensor includes: a housing having a first side and a second side, the second side being opposite to the first side and spaced therefrom, the square two-by-two photodetector array being located proximal to the second side within the housing; and an aperture extending through the first side of the housing and configured to expose the four photodetectors (18a-d) of the square two-by-two photodetector array to an incident light from the light emitting device, wherein each of the four photodetectors (18a-d) is square shaped, and wherein the aperture has the same square shape and dimensions as each photodetector, and wherein the aperture is spaced from the square two-by-two photodetector array by a distance equal to a width or length of the square shape of each photodetector; and a housing having a first side and a second side, the second side being opposite to the first side and spaced therefrom, the square two-by-two photodetector array being located proximal to the second side within the housing; and an aperture extending through the first side of the housing and configured to expose the four photodetectors (18a-d) of the square two-by-two photodetector array to an incident light from the light emitting device, wherein each of the four photodetectors (18a-d) is square shaped, and wherein the aperture has the same square shape and dimensions as each photodetector, and wherein the aperture is spaced from the square two-by-two photodetector array by a distance equal to a width or length of the square shape of each photodetector; and wherein the processor is configured to detect an angle of incidence of a light source based on light intensity readings detected at one or more regions of a light-receiving surface of the square two-by-two photodetector array that are illuminated by light entering the sensor through the aperture.