Orb

The orb is the angular tolerance around an aspect — how far from the exact angle two planets can be and still be considered in aspect. Different schools use different orbs, but a working middle ground is: 8° for major aspects (conjunction, opposition, trine, square), 5° for sextiles, 2-3° for minor aspects. The tighter the orb, the louder the aspect: a 0.5° square is dramatically more prominent in the chart than a 7° square. Some astrologers vary orbs by planet — the luminaries (Sun and Moon) get wider orbs (10°) because they're the loudest bodies; outer planets get tighter orbs in transits because their slowness makes any aspect to a natal point linger for months. The Astro Diary uses a configurable orb factor in user preferences so that more conservative practitioners can tighten thresholds while traditionalists can keep them wide.