The Eyes of Clavius
BEST TIME TO SEE: Early hours of 2 April
Clavius is a large crater visible in the southern region of the Moon’s Earth-facing side. Its 225km-diameter rim appears heavily foreshortened from Earth due to its proximity to the Moon’s southern limb.
The rim appears interrupted by smaller craters such as 53km Porter in the northeast and 55km Rutherfurd in the southeast. Inside Clavius is a curving arc of craterlets that appears to start at Rutherfurd arcing round to 28km Clavius D, 21km Clavius C, 13km Clavius N and 12km Clavius J.
Clavius C and D have rims raised above Clavius’s floor. At certain times when the terminator is crossing Clavius, the C and D rims will catch the light of the early lunar dawn before it’s had a chance to flood the main crater’s floor. When this happens, the rims appear like large illuminated circles hovering in the dark. This forms the clair-obscur effect, a trick of the light, known as the Eyes of Clavius.
The eyes occur when the lunar terminator is at co-longitude 15˚.
This will be the case in the early hours of 2 April when the effect should be visible through a telescope’s eyepiece. The Moon will be at the 56% waxing gibbous phase at this time.