If you lived at the North Pole and look striaght up to the zenith, then all the stars in the sky move around the point directly above you Very near this point is a star 0 called the Pole Star All the stars in the sky seem to rotate around this point 90 degrees from the zenith is the horizon At the North Pole, the horizon also marks the position of the celestial equator If you live somewhere else on the Earth, then the Pole Star appears not at the zenith, but at an angle to the horizon equal to your latitude The celestial equator is now no longer at the horizon, but somewhere in the sky above the horizon If you live on the equator, then the Pole Star is now on the horizon, and the celestial equator is directly above you
The projection of Earth's equator onto the sky If you were standing on Earth's equator, the celestial equator would extend from eastern horizon, directly over your head (zenith), then to the western horizon Astronomers use an imaginary projection of Earth's latitude and longitude, called the celestial sphere, to locate planets, stars, star clusters, nebulae and galaxies
great circle that is a projection of the Earth's equator onto the sky Always intercepts horizon at exact East and exact West point Its meridian altitude = 90\deg -- observer's latitude We see one-half of its circle at a time (12 hours worth)
This is simply the projection of the Earth's equator, onto the celestial sphere The sphere is thus divided into Northern and Southern hemispheres in the same way as the Earth Declination is measured North or South of the celestial equator in degrees so that the celestial equator has a declination of 0° along its whole length See also celestial pole
the great circle of the celestial sphere all points of which are 90o from the poles It is the plane of the earth's equator projected onto the celestial sphere
The projection onto the celestial sphere of the Earth's equatorial plane, separating northern and southern hemispheres, and representing zero degrees of declination
The primary great circle of the celestial sphere in the equatorial system, everywhere 90° from the celestial poles; the intersection of the extended plane of the equator and the celestial sphere Also called equinoctial
The sky can be imagined as a sphere surrounding Earth A line projected out from the equator of Earth defines the celestial equator of the celestial sphere Standing on Earth's equator, the celestial equator would appear directly overhead
The imaginary line projected in the sky which is directly above the Earth's equator[?] At the equator, this line goes directly overhead, through the zenith[?] At either the north or south pole, this line forms a circle at the level of the horizon See also: celestial pole, ecliptic, meridian