Astronomically, the zodiac defines a belt of space extending 9° either side of the ecliptic, within which the orbits of the Moon and the principal planets remain [REF].
The convention of measuring celestial longitude within individual signs was still being used in the mid-19th century,[REF] but modern astronomy now numbers degrees of celestial longitude from 0° to 360°, rather than 0° to 30° within each sign.