Note: Constellation date is the date when the sun passes through each constellation. Constellation date and solar term date are bothGregorian calendar。
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The ecliptic and the zodiac
EclipticyesAnnual apparent motion of the sunThe path on the celestial sphere passes through 13 of the 88 constellations, which are collectively called the zodiac constellations.Other EarthplanetThe orbits around the sun intersect into a range of 1 °~3 ° (exception:Mercury7 °)Rail inclinationThe area of 8 ° on both sides of the ecliptic and 16 ° in width iszodiacAll the planets in the sky are in it.
Huang Jing and Gong
Zodiac
The zodiac is used in east-west directionYellow meridianIs represented by, and is specified asVernal equinoxFrom east to west, the longitude is 0 ° to 360 °.Divide the ecliptic into 12 equal segments, each 30 °, that isZodiacThe sun passes through each house in about 30 days.The 12 zodiac signs are artificially divided, so there are only 12 signs, notOphiuchus 。So Ophiuchus is one of the zodiac constellations, but notZodiacone of.
However, the zodiac constellation is long and short in the east-west direction. The longest one is Virgo, which is 44 ° long in the ecliptic, accounting for about 1/8 of the total length of the ecliptic. The sun passes through Virgo for 44 days;The shortest one is Scorpio, which is only 5 ° long, about 1/9 of Virgo. The time when the sun passes through Scorpio is only 7 days.Therefore, the house and the constellation cannot be confused.
precession of the equinoxes
Since the earth is not a normal sphere, but a rotating ellipsoid, the equatorial radius is about 21 kilometers larger than the polar radius, and there is an angle between the equatorial plane of the earth and the ecliptic plane, with an average of 23.5 °, so a celestial body like the earth will change its axis of rotation under the action of planetary gravity, which is called the earth's axis.This change is very slow, with a period of about 25800 years. It was first discovered by the Greek astronomer Hipparchus around 150 BC.
The precession causes the vernal equinox to move westward about 50.2 ″ every year along the ecliptic, which is a very small angle.It will take about 400 years for the second hand to rotate 6 ° every second and the vernal equinox to move 6 ° on the ecliptic.But from a historical perspective, the influence of precession is not small.The star house was divided 4000 years ago, when all constellations were basically located in their respective star houses.But because of the precession, the constellations are moving, and the position of the house of stars is always unchanged.As a result, after 4000 years, modern constellations have been misaligned with their own star houses, resulting in the mismatch between constellations and star houses, as shown in the table above.
