Using data collected by the MACRO experiment during the years 1989–1996, we show evidence for the shadow of the Moon in the underground cosmic ray flux with a significance of 3.6σ. This detection of the shadowing effect is the first by an underground detector. A maximum-likelihood analysis is used to determine that the angular resolution of the apparatus is $0.9°\pm 0.3°.$ These results demonstrate MACRO’s capabilities as a muon telescope by confirming its absolute pointing ability and quantifying its angular resolution.

• Received 11 June 1998

DOI:https://doi.org/10.1103/PhysRevD.59.012003