Noun explanation: celestial pole, zodiac, vernal equinox. (The above is related to astronomy. )

The zenith is not the zenith. It is the intersection of celestial axis and celestial sphere, which is divided into north celestial pole and south celestial pole. Now the north celestial pole is near Polaris, but the position of the north celestial pole has been changing because of the precession of the earth.

When we look at the earth, the sun goes around the earth once a year. This kind of movement is called the apparent movement of the sun (not the real movement), and the projection of the apparent movement route of the sun on the celestial sphere is the ecliptic. In other words, the great circle where the ecliptic plane intersects the celestial sphere is the ecliptic. The zodiac is a constellation near the ecliptic on the celestial sphere.

The vernal equinox is the rising intersection of the ecliptic and the celestial equator, and the right ascension and declination of the vernal equinox are both 0. The vernal equinox is the day when the sun passes through vernal equinox in the annual movement (apparent movement) of the sun, that is, the declination of the sun is zero.