Home » Zodiac » Celestial Coordinate Systems Zodiac Celestial Coordinate Systems of latitude and longitude are used in astronomy to find any point located on the earth's surface. In ancient times astronomers thought that the sky was an enormous sphere at the center of which the Earth was located. According to them, the stars were bound to the huge sphere, and when it rotated for a single time everyday, all the stars would appear to rise and set across the sky. It is a known fact in the modern age, that the existence of this sphere is not true. The planets and stars are located very far away from the earth and their motion is due to the spinning action of the Earth on its axis. However the picture of this celestial sphere, enveloping our planet is a helpful concept for astronomers. They have produced a grid of reference points and lines on the celestial sphere in order to ascertain the position of every planet, star and galaxy.

The different zodiac celestial coordinate systems are important in the field of astronomy and the most significant of them are Equatorial Coordinate System and Ecliptic Coordinate System. In the equatorial coordinate system, the plane of reference is undoubtedly the Earth’s equator.

The poles are located at the intersection point of the pole of the celestial sphere and the Earth’s pole. Every point on the Earth, and the latitudes and longitudes are imaginary. The poles are South Celestial Pole or SCP and the North Celestial Pole or NCP. The circle drawn at the intersection point of the plane of the celestial sphere and the Earth’s equator is known as the celestial equator. The big circle through the object like a star and the celestial poles is the Hour Circle of the object. The other great circle passing through the zenith and the celestial poles is the Meridian Circle. In this system the coordinates are given by the angle between the object and the celestial equator (or declination) and the right ascension, which is the angle assessed from the Vernal Equinox (a reference direction) to the hour circle of the object.

In the coordinate system of the ecliptic, the plane of reference is the Earth’s orbit. The coordinates which are employed are celestial latitude and celestial longitude. The first one is the vertical distance of the object from the plane of ecliptic, measured in angles. The great circle which passes through the winter and summer solstices is known as the solstitial colure. The ecliptic sphere or the zodiac sphere is the sphere, which results from casting the plane of the Earth’s orbit and the poles. The ecliptic plane passes through the central points of both the Earth and the Sun. It is a representation of the route the Sun’s center taken every year on the celestial sphere.

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