Participants in an Operation Nanook-Nunalivut patrol, an Arctic military exercise, near Rankin Inlet in the Nunavut territory of Canada. photos:  Nasuna Stuart-Ulin/nyt

A moon dog hung low over the horizon. It showed up on the first day of the Canadian soldiers' patrol, and the Inuit rangers guiding them in the country's far north spotted it right away: Ice crystals in the clouds were bending the light, making two illusory moons appear in the sky.