 This paper proposes a novel method for synchronizing sensor nodes in wireless sensor networks, WSNs, which uses cosmic ray muons rather than radio frequency signals. This method is able to provide accurate synchronization over a wide range of environments, including those where radio frequency signals cannot be used due to obstructions. Experimental results show that the proposed system can achieve a resynchronization frequency and precision of 60 Hz and plus or minus for 0.3 NS, standard deviation. This method could be applied to a variety of applications, such as structural health monitoring of aerospace structures, and could potentially lead to the development of new critical and useful applications of WSNs in a wider range of environments. This article was authored by Hiroyuki K. M. Tanaka.