Neptune
Neptune governs imagination, the dissolving of boundaries and illusions. It was discovered in 1846, by calculation, before it was observed.
Governs
Neptune describes the area where a person finds inspiration and where they deceive themselves: creativity, compassion, faith, but also illusions, addictions and self-deception.
Its cycle is about 165 years, with roughly fourteen years in each sign. Like Uranus, it is a generational planet, and its sign is the same for everyone of the same age.
In the signs and houses
Neptune's house shows where a person tends to idealize and not see reality: in the seventh, a partner; in the second, money; in the sixth, work.
In astrology, Neptune's aspects to the Sun and the Moon are considered a sign of artistic sensitivity and, at the same time, of vulnerability to other people's influence.
Strong and weak placements
Ruler of Pisces in the modern tradition; in the classical tradition, the sign was ruled by Jupiter.
The story of Neptune's discovery is a good illustration of the difference between astronomy and astrology: the planet was found by calculating the perturbations in Uranus's orbit, a method that is testable and reproducible. Its astrological meaning was assigned afterward.