where R s is the radius of the star, R o is the occulting object's radius, and r is the distance from the star to the occulting object. For Earth, on average L is equal to 1.384 × 10 km, which is much larger than the Moon's semimajor axis of 3.844 × 10 km. Hence the umbral cone of the Earth can completely envelop the Moon during a lunar eclipse. If the occulting object has an atmosphere, however, some of the luminosity of the star can be refracted into the volume of the umbra. This occurs, for example, during an eclipse of the Moon by the Earth—producing a faint, ruddy illumination of the Moon even at totality.