Bai Dao

[bái dào]

term in astronomy

open 4 entries with the same name

Baidao, astronomy Term Moon The running track of. White and ecliptic Angle of intersection It varies from 4 ° 57 ′ to 5 ° 19 ′, average value It is about 5 ° 09 ′, and the change period is about 173 days. Due to the gravity of the sun on the moon, the line between the two intersection points moves westward along the opposite direction of the ecliptic and the moon. This phenomenon is called Intersection retrogression 。

The intersection moves 19 ° 21 'every year, and it will complete one week in about 18.6 years. The impact of this phenomenon on the earth nutation And tides.

Chinese name: Bai Dao
Definition: Moon Of revolution Included angle between plane and earth's revolution
Angle of intersection: Change between 4 ° 57 ′ and 5 ° 19 ′
average value: About 5 ° 09 ′

Cycle of change: About 173 days
Complete one week: 18.6 years
Time of publication: 1998^[1]
See publications: Astronomical Terms (Second Edition), Science Press

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Bai Dao - Introduction

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The angle of intersection between the ecliptic and the equator is the ecliptic angle

The revolution plane of the moon is not coincident with that of the earth, and there is an angle of about 5 degrees and 9 minutes.

Baidao Diagram

So it doesn't happen every lunar month solar eclipse and lunar eclipse 。 Only when the moon is on the same line with the sun and the earth, and the moon is near the intersection of two planes, will a solar eclipse or lunar eclipse occur. Because the distance between the moon and the intersection of two planes is not fixed during each solar eclipse, and earth rotation The resulting angle is not fixed, so Eclipse zone The location on the earth is not fixed. The moon goes around Earth revolution The track of celestial sphere Projection on. It is a big circle on the celestial sphere and intersects the ecliptic at two points. The intersection where the moon moves from the south of the ecliptic to the north of the ecliptic on the white path is called Ascending intersection The other intersection opposite this is called Descending point 。 Ecliptic Angle of intersection It varies from 4 ° 57 ′ to 5 ° 19 ′, average value It is about 5 ° 9 ′, and the change period is about 173 days. Due to the gravity of the sun on the moon, the line between the two intersections (i.e. the intersection line) moves westward in the opposite direction of the ecliptic and the moon's movement, resulting in the moon not returning to its original position after a circle. Intersection line The phenomenon of westward movement is called Intersection retrogression 。 The intersection line moves 19 ° 21 'every year, completing one cycle in about 18.6 years, which causes the lunar Declination Change. When the ascending intersection point and Vernal equinox (See Equinox ）When it coincides, the ecliptic is located between the Whiteline and the equator, and the intersection angle between the Whiteline and the equator is Yellow declination angle And Yellow white angle Sum of; When Descending point When it coincides with the vernal equinox, the white path lies between the equator and the ecliptic, and the intersection angle between the white path and the equator is the difference between the yellow and red angles and the yellow and white angles.

White Way - Creating Meaning

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Bai Dao

First of all, the orbit of the moon is not a circle in space, but if it is projected onto the celestial sphere Then it must be a big circle on the celestial sphere, because Lever theorem The existence of the moon Earth and Moon The two focal points of the orbit of revolution must be in a straight line, while the celestial sphere Spherical center It is generally believed that it is the earth, and the radius of the earth is far less than the radius of the moon's orbit, so the white road is a big circle on the celestial sphere. The equator is also a big circle on the celestial sphere, so their centers coincide.

White Road - Location

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Yellow white angle It is about 5 degrees, and its intersection point moves continuously along the ecliptic with time, so the intersection angle between the white path and the equator is in a state of constant change, the minimum is about 18 degrees, the maximum is about 28 degrees, but these two Extreme value And its nearby values are rarely observed, because it is rarely so coincidental: Yellow white intersection It is completely coincident with the yellow and red intersections, and the distance between the moon and these two intersections on the celestial sphere is 90 degrees.

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