Rahu and Ketu illustrated using the Celestial Sphere

This video illustrates the astronomical definition of Rahu and Ketu using a Celestial Sphere.

Rahu and Ketu are not physical bodies but merely points in space. These are the two points in space where the orbit of the Sun and the Moon intersect (in a geocentric model). The point where the Moon moves from the south to the north of the Ecliptic is Rahu; the point where the Moon moves from the north to the south of the Ecliptic is Ketu. In English, these points are called Ascending Node of the Moon and Descending Node of the moon respectively.

This concept is best illustrated using a celestial sphere. The celestial sphere is all the space that surrounds the earth. It is modelled as a sphere of infinite radius. Stellarium illustrates the celestial sphere by using curved longitude and latitude lines (similar to those used on a globe of the Earth). Using such a representation, it is possible to show North on the top and South on the bottom in the conventional way. This helps to illustrate the Moon moving north of the Ecliptic (Rahu) and south of the Ecliptic (Ketu).

0:00 North and south of the Ecliptic
2:25 Definition of Rahu and Ketu
4:03 Celestial sphere
6:19 Rahu and Ketu on celestial sphere