Title: Meridian (geography)
Content:  circle, the meridian on the opposite side of the earth from Greenwich, the antimeridian, forms the other half of a circle with the one through Greenwich, and is at 180° longitude  near the International Date Line (with land mass and island deviations for boundary reasons). The meridians from West of Greenwich (0°) to the antimeridian (180°) define the Western Hemisphere and the meridians from East of Greenwich (0°) to the antimeridian (180°) define the Eastern Hemisphere. Most maps show the lines of longitude. The position of the prime meridian has changed a few times throughout history, mainly due to the transit observatory 
Title: IERS Reference Meridian
Content:  opposite, stations must move in opposite directions by the same amount. The 180th meridian (the meridian at 180° both east and west of the Prime Meridian) is opposite the IERS Reference Meridian and forms a great circle with it dividing the earth into Western Hemisphere and Eastern Hemisphere. Universal Time is notionally based on the WGS84 meridian. Because of changes in the rate of Earth's rotation, standard international time UTC can differ from the mean observed solar time at noon on the prime meridian by up to 0.9 of a second. Leap seconds are inserted periodically to keep UTC close to Earth's angular position relative to the Sun; see mean solar time.
Title: Geographic coordinate system
Content:  of a point on Earth's surface is the angle east or west of a reference meridian to another meridian that passes through that point. All meridians are halves of great ellipses (often called great circles), which converge at the North and South Poles. The meridian of the British Royal Observatory in Greenwich, in southeast London, England, is the international prime meridian, although some organizations—such as the French Institut national de l'information géographique et forestière—continue to use other meridians for internal purposes. The prime meridian determines the proper Eastern and Western Hemispheres, although maps often divide these hemispheres further west in order to keep the Old World on a single side. The 
Title: 90th meridian west
Content:  The meridian 90° west of Greenwich is a line of longitude that extends from the North Pole across the Arctic Ocean, North America, the Gulf of Mexico, Central America, the Pacific Ocean, the Southern Ocean, and Antarctica to the South Pole. In Antarctica, the meridian defines the western limit of Chile's territorial claim. The land further west is not claimed by any nation. The 90th meridian west forms a great circle with the 90th meridian east, located midway between the Prime meridian and the 180th meridian; thus, the center of the Western Hemisphere is on this meridian. In the United States, the Mississippi River runs close to the 90th meridian, crossing the meridian several times. The cities of St. Louis, Memphis and New Orleans are all close to the meridian.
Title: 122nd meridian west
Content:  The meridian 122° west of Greenwich is a line of longitude that extends from the North Pole across the Arctic Ocean, North America, the Pacific Ocean, the Southern Ocean, and Antarctica to the South Pole. 122°W is the Seventh Meridian of the Dominion Land Survey in Canada. The 122nd meridian west forms a great circle with the 58th meridian east.
Title: 142nd meridian west
Content:  The meridian 142° west of Greenwich is a line of longitude that extends from the North Pole across the Arctic Ocean, North America, the Pacific Ocean, the Southern Ocean, and Antarctica to the South Pole. The 142nd meridian west forms a great circle with the 38th meridian east.
Title: 152nd meridian west
Content:  The meridian 152° west of Greenwich is a line of longitude that extends from the North Pole across the Arctic Ocean, North America, the Pacific Ocean, the Southern Ocean, and Antarctica to the South Pole. The 152nd meridian west forms a great circle with the 28th meridian east.
Title: 20th meridian west
Content:  The meridian 20° west of Greenwich is a line of longitude that extends from the North Pole across the Arctic Ocean, Greenland, Iceland, the Atlantic Ocean, the Southern Ocean, and Antarctica to the South Pole. The 20th meridian west forms a great circle with the 160th meridian east. In Antarctica, the meridian defines the border between the British Antarctic Territory and Queen Maud Land. Between the 5th parallel north and the 60th parallel south it forms the eastern boundary of the Latin American Nuclear-Weapon-Free Zone.
Title: 82nd meridian west
Content:  The meridian 82° west of Greenwich is a line of longitude that extends from the North Pole across the Arctic Ocean, North America, the Gulf of Mexico, the Caribbean Sea, Panama, the Pacific Ocean, the Southern Ocean, and Antarctica to the South Pole. The 82nd meridian west forms a great circle with the 98th meridian east.
Title: 94th meridian west
Content:  The meridian 94° west of Greenwich is a line of longitude that extends from the North Pole across the Arctic Ocean, North America, the Gulf of Mexico, Central America, the Pacific Ocean, the Southern Ocean, and Antarctica to the South Pole. The 94th meridian west forms a great circle with the 86th meridian east. In the United States, the meridian runs just east of, and approximately parallel to, part of the border of Texas with Arkansas and Louisiana.

Question: where is the meridian that is opposite the prime meridian located?
Answer: the 180th meridian.
antimeridian.