How Alaska’s Semisopochnoi Island Became the Easternmost Point in the U.S.

You might think that the easternmost point of the United States is somewhere in Maine, but you would be wrong. It’s actually in Alaska, on a remote island called Semisopochnoi. How is that possible? It’s all because of how we define our global coordinate system.

Semisopochnoi Island is part of the Rat Islands group in the western Aleutian Islands of Alaska. The island is uninhabited and provides an important nesting area for maritime birds. It’s of volcanic origin, containing several volcanoes including Mount Young. The island has a land area of 85.558 square miles, measuring 11 miles in length and 12 miles in width.

The reason Semisopochnoi Island is considered the easternmost point in the U.S. is because of its location relative to the 180th meridian, which is the line of longitude that defines the boundary between the Eastern and Western Hemispheres. At 179°46′ East (+179.7667) (in the Eastern Hemisphere), the easternmost tip of Semisopochnoi is, by longitude, the easternmost land location in the United States and North America. Semisopochnoi is located 14 minutes (0.2333 degrees) or 9.7 miles (15.6 km) west of the 180th meridian.

This might seem confusing, but it’s all about perspective. When we think of the globe, we often imagine it with the Prime Meridian (0…