What Aspects Are

An aspect is simply how many degrees apart two positions are — something you can read by measuring an angle. The usual reading treats an aspect as a conversation between two planets: 180 degrees apart is face to face, 90 is catching on each other, 120 and 60 are going along with each other.

A quick way to estimate: count how many signs lie between the two. Six apart is roughly an opposition, four a trine, three a square, two a sextile. Sun in Aries and Moon in Leo are four signs apart, so start by guessing a trine.

Then check the actual degrees. This app measures the real degrees, and the aspects listed on the chart page are already worked out, so you can check your guess against them.

What the old texts say: Book I ch. 13 of Ptolemy's Tetrabiblos, “Of the Aspects of the Signs,” is precise — opposition spans two right angles, six signs, 180 degrees; trine one and a third right angles, four signs, 120 degrees; square one right angle, three signs, 90 degrees; sextile two-thirds of a right angle, two signs, 60 degrees.

A circle is 360 degrees. 180 is a half, 120 a third, 90 a quarter and 60 a sixth. Held this way, the four aspects are easy to remember, and you can tell which one a figure is at a glance.

This app computes exactly these four, plus the conjunction: two bodies bunched together, 0 degrees apart. The chart page lists all five together.

Astrology today often reads them like this: a conjunction blends two forces; an opposition is a tug of war that asks for balance; a square catches and pushes you to act; a trine runs easily, without effort; a sextile is an opening you have to reach for.

What the old texts say: the same chapter gives the reason. Opposition is the obvious one, because the two places sit on one straight line. The rest come from applying the most important musical ratios to the right angle: a half and a third applied to opposition give the square, the sextile and the trine. The text adds that trine and sextile are called harmonious because they join signs of the same kind, all masculine or all feminine, while square and opposition are not.

Two bodies are rarely an exact round angle apart, so you need a range for how far off still counts, called the orb. This app uses a common modern table: in a birth chart, 8 degrees for conjunction and opposition, 6 for square and trine, 4 for sextile; transits are read more tightly, 1 degree in general and 2 for the Sun and Moon. Every report records which version of the table it used.

So if another source shows you different aspects, usually the orbs are set differently. When reading your own chart, start with the aspects closest to exact; they are usually the ones most worth reading first.

What the old texts say: Book I ch. 13 gives exact angles: opposition 180, trine 120, square 90, sextile 60 degrees.