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The 180th meridian or antimeridian [1] is the meridian 180° both east and west of the prime meridian in a geographical coordinate system. The longitude at this line can be given as either east or west. On Earth, the prime and 180th meridians form a great circle that divides the planet into the Western and Eastern Hemispheres.
Earth's rotation imaged by Deep Space Climate Observatory, showing tilt. Earth's rotation or Earth's spin is the rotation of planet Earth around its own axis, as well as changes in the orientation of the rotation axis in space. Earth rotates eastward, in prograde motion. As viewed from the northern polar star Polaris, Earth turns counterclockwise.
A prime meridian is an arbitrarily chosen meridian (a line of longitude) in a geographic coordinate system at which longitude is defined to be 0°. Together, a prime meridian and its anti-meridian (the 180th meridian in a 360°-system) form a great circle.
Any planetary-sized body 180 degrees from Earth should also have been visible to some space probes, such as NASA's STEREO coronagraph probes (two spacecraft launched into orbits around the Sun in 2006, one farther ahead of and one behind the Earth's orbit) which would have seen the Counter-Earth during the first half of 2007. The separation of ...
Assuming a spherical Earth, a meridian is a great semicircle on Earth's surface. Adopting instead a spheroidal or ellipsoid model of Earth, the meridian is half of a north-south great ellipse . The length of a meridian is twice the length of an Earth quadrant , equal to 20,003.93 km (12,429.87 mi) on a modern ellipsoid ( WGS 84 ).
Viewed from a vantage point above the Sun and Earth's north poles, Earth orbits in a counterclockwise direction about the Sun. The orbital and axial planes are not precisely aligned: Earth's axis is tilted some 23.44 degrees from the perpendicular to the Earth–Sun plane (the ecliptic ), and the Earth-Moon plane is tilted up to ±5.1 degrees ...
An object with an axial tilt up to 90 degrees is rotating in the same direction as its primary. An object with an axial tilt of exactly 90 degrees, has a perpendicular rotation that is neither prograde nor retrograde. An object with an axial tilt between 90 degrees and 180 degrees is rotating in the opposite direction to its orbital direction.
While Airy's local vertical, set by the apparent centre of gravity of Earth still points to (aligns with) the modern celestial meridian (the intersection of the prime meridian plane with the celestial sphere), it does not pass through Earth's rotation axis. As a result of this, the ITRF zero meridian, defined by a plane passing through Earth's ...