All the planets move round the sun in orbits whose planes are
slightly inclined to that of the earth, the plane of Mercury having
the greatest inclination of 6°. The plane of the moon's orbit round
the earth is also inclined at 5° 9' to the ecliptic. The orbits of
the moon and all the planets must necessarily intersect the plane of
the earth's orbit on the ecliptic at two points, and these are called
the nodes of the moon and each planet respectively. In consequence
of the inclination being so slight, though the course of the moon and
planets is not actually on the ecliptic, they are all so close to it
that they are included in the belt of the zodiac. Thus the moon and
all the planets follow almost the same apparent course on the zodiac
or belt round the ecliptic in the changes of position resulting from
their own and the earth's orbital movements with reference to what
are called the fixed stars.