antimeridian

Noun

antimeridian (plural antimeridians)

1. The reference line at 180° longitude, on the opposite side of earth to the prime meridian.
   • On the opposite side of the Earth from Greenwich is the antimeridian, a line of longitude that is 180° both east and west of the prime meridian. It cuts through parts of eastern Russia, the Fiji Islands and the middle of the Pacific Ocean.2015, Simon Guerrier, Dr. Marek Kukula, The Scientific Secrets of Doctor Who, Random House, →ISBN

   Synonyms:

   Greenwich antimeridian

2. A meridian of longitude opposite to any given meridian used as a point of reference.
   • 123° west is the antimeridian of the 57° east meridian.
   • The antimeridian contains your nadir and the opposite celestial pole for your hemisphere. The local meridian and the antimeridian together form the great circle simply called the meridian.2006, William Millar, The Amateur Astronomer's Introduction to the Celestial Sphere, Cambridge University Press, →ISBN, page 24