Ortac is a small uninhabited islet about 5 kilometres west of the coast of Alderney near to the islet of Burhou. It measures roughly 50 by 70 metres, and rises 24 metres above the sea level.

Alderney is the northernmost of the inhabited Channel Islands. It is part of the Bailiwick of Guernsey, a British Crown dependency. It is 3 miles (5 km) long and 1+1⁄2 miles (2.4 km) wide.