What the trine is
A trine is an angular separation of 120° — one-third of the circle. It is the most harmonious of the aspects: the two planets are in the same element, so their energies flow together with complete ease. Whatever the planets signify comes naturally, as innate talent or effortless grace.
The trine is the aspect of gift — but a gift so easy it is often unnoticed and underused.
How the trine works
A trine grants effortless cooperation between two functions of the psyche. It gives ability, luck and flow in the area involved. Its shadow is precisely its ease: because trines require no effort, they can breed complacency, and their talents may go undeveloped unless the harder aspects (squares) push the person to use them.
By transit and synastry
By transit, a trine brings a period of ease and opportunity — favourable, low-effort, but rarely a catalyst on its own. In synastry it shows where two people simply "get" each other, an area of natural understanding and comfort. Harmony, sometimes to the point of taking each other for granted.