R Doradus is a red giant variable star in the far-southern constellation Dorado. Its distance from Earth is 178 light-years. Having a uniform disk diameter of 57±5 mas, it is thought to be the extrasolar star with the largest apparent size as viewed from Earth.

The angular diameter, angular size, apparent diameter, or apparent size is an angular distance describing how large a sphere or circle appears from a given point of view. In the vision sciences, it is called the visual angle, and in optics, it is the angular aperture. The angular diameter can alternatively be thought of as the angular displacement through which an eye or camera must rotate to look from one side of an apparent circle to the opposite side. Humans can resolve with their naked eyes diameters down to about 1 arcminute. This corresponds to 0.3 m at a 1 km distance, or to perceiving Venus as a disk under optimal conditions.