Lunar node

The South Node or Dragon points are the intersections of the Moon's orbit to the ecliptic plane.

The ascending lunar node ( common symbol: ☊ ) is one in which the moon goes from the southern to the northern side of the ecliptic. In the South Node ( ☋ ) changes of the moon on the southern side of the ecliptic. The connection between the two nodes is called nodal line.

The interval between two successive passages of the Moon through the ascending node is called Drakonitischer month.

Nodes and eclipses

Only in the vicinity of a passage of the moon through one of the nodes - with simultaneous full or new moon - is a lunar or solar eclipse possible. The time interval between two passages of the sun through the same lunar node is called the eclipse year.

From the image of the dragon swallows the sun or the moon, the old term kite point ( "dragon" in Latin draco ) is derived from: The Moon's Nodes were also known as dragon's head (caput draconis, the ascending lunar node ) or dragon's tail ( cauda draconis, Descending known lunar node ) and had a special meaning. The two points of the lunar orbit with the largest northern and southern ecliptic latitude (ie the greatest distance from the ecliptic ) were called dragon belly ( Venter draconis ); they differ from the node by 90 ° in length.

The same etymological meaning is in the " ecliptic " (Greek ékleipsis - literally " concealment, obliteration "). It is also found in the Chinese- Confucian mythology in Xi and He,羲 和, the heavenly officials for sun and moon. This myth however, has no known relationship with the constellation " Dragon".

The dragon point names as the Drakonitischen period, ie the general period of two passes of a celestial object by its nodes.

The Drakonitische month

The length of the drakonitischen month is given as 27.21222 days. The 27 days, 5 hours, 5 minutes and 35.8 seconds.

The drakonitische month is used to calculate eclipse cycles, the regular repetition of solar and lunar eclipses.

The lunar nodes move through the precession of the lunar orbital plane annually by about 19.3 ° decline in the ecliptic. Thus, the drakonitische month to 0.1095 days (2h 37.6 m) is shorter than the - related to the equinox - Tropical month.

A complete revolution of the nodes in the ecliptic takes 6798 days or 18.61 years.

Moon's Nodes and nutation

The lunar nodes drift causes a change in the position of the lunar orbit on the celestial sphere of an observer. If one of the lunar nodes ( in ascending or descending ) with the vernal equinox together, so there is an extreme position of the web: The equatorial plane close to the ecliptic at an angle of 23 ° 27 ' ( obliquity of the ecliptic ) that the lunar orbit is in the middle 5 ° 9 'with respect to the ecliptic inclined (inclination of the lunar orbit ). The two values ​​add up to a maximum declination of the moon of 28 ° 36 ' (minimum 18 ° 17' ). The extrema of the cycle are also referred to as a moon turning.

The gravitational effect of the moon that hovers around these extreme situations, causes nutation, a periodic Achsschwankung the earth with the same period of 18,613 years, which is therefore called nutation.