The zodiac signs are arranged along the ecliptic, and the intersection angle between the ecliptic and the celestial equator is 23.4; The two intersections of the ecliptic and the celestial equator are the vernal equinox and the autumnal equinox. In the ecliptic coordinate system, the longitude of celestial bodies is measured eastward along the ecliptic from the vernal equinox, with positive north latitude and negative south latitude. The distance between the south and north poles and the corresponding celestial pole is 23.4.
Because the earth's revolution is perturbed by the moon and other planets, the orbit of the earth's revolution is not a strict plane, that is, it produces irregular continuous changes in space, which includes many short-term and a slow long-term movements. Short-period motion can be averagely eliminated in a certain time, and the orbital plane with periodic motion eliminated is called instantaneous average orbital plane. The strict definition of the ecliptic is: the great circle where the instantaneous average orbital plane of the center of mass of the Earth-Moon system revolves around the sun and intersects the celestial sphere. The ecliptic is the base circle of the ecliptic coordinate system on the celestial sphere.
Zodiac plane (ecliptic)
Plane) refers to the orbital plane of the earth around the sun, and the intersection angle with the equatorial plane of the earth is 23 27'. Because the gravity of the moon and other planets affects the revolution of the earth, the position of the ecliptic plane in space is always changing irregularly. But in change, this plane always passes through the center of the sun at any time. The great circle where the ecliptic plane intersects the celestial sphere is called the ecliptic.
zodiac
The annular region on the north and south sides of the ecliptic on the celestial sphere. There are twelve constellations in the zodiac, and the sun always appears in the same constellation in a month. According to the arrangement order of the constellations, the sun passes through one of the twelve constellations every month, and the trajectory of the sun passing through the zodiac is called the zodiac.
In astronomy, celestial coordinate system is a coordinate system that describes the position of objects in the sky. Similar to the geographical coordinate system we use on the earth's surface, celestial coordinate system changes with the grid of coordinates projected on the celestial sphere. The plane that divides the sky into two equal hemispheres along the great circle is called the fundamental plane, and this coordinate system will only change because of the difference of the fundamental plane. The basic plane in the geographical coordinate system is the equator of the earth. The name of each coordinate system depends on the choice of basic principles. The following are different coordinate system names:
Horizon coordinate system
Equatorial coordinate system
ecliptic coordinate system
Galaxy coordinate system
Supergalaxy coordinate system
obliquity of the ecliptic
The equatorial plane of the earth does not coincide with the ecliptic plane, but there is an intersection angle (dihedral angle), namely the ecliptic angle. In 2000, this intersection angle was 23 26' 21".
Equinox, autumnal equinox, summer solstice and winter solstice.
These points are on the geocentric celestial sphere.
One of the two intersections between the ecliptic and the celestial equator is the first point of Aries, namely the vernal equinox, and the second intersection is the first point of Libra, namely the autumnal equinox. These two points are collectively called the bisector.
One of the two points farthest from the celestial equator on the ecliptic is the first point of Cancer House, which is the solstice in summer, and the second intersection point is the first point of Capricorn House, which is the solstice in winter. These two points are collectively called the second solstice.