In astrology, an orb is the number of degrees of difference from an exact angle that is allowable for planets to still be considered in aspect to one other.
For example, an opposition between two planets exists when the planets are 180 degrees from each other on a natal or horary chart. Two planets may still generally be considered in opposition with a variation of up to 7 degrees. Different astrologers allow different orbs in computing aspects.
- March, Marion and McEvers, Joan. The Only Way to Learn Astrology. San Diego, CA: ACS Publications.