Tropic of Cancer
From Memory Alpha, the free Star Trek reference
The Tropic of Cancer is a geographical region on Earth which is defined as the tropical region of the planet situated north of the equator. In the Pacific Ocean, the Tropic of Cancer was the location of several islands, such as Hawaii and Midway Island. The International Date Line also ran on a north-south axis through the Tropic of Cancer.
In 2254, when the Talosians downloaded a map of the Pacific region from the library computer of the USS Enterprise, the Tropic of Cancer was one of the areas which was displayed. (TOS: "The Cage")
