Neptune was discovered in 1846, and given the Roman name for Poseidon, god of the oceans and seas. Because of its deep blue color, its name is an apt assignment. In astrology, it represents the depths of the imagination and emotions, as well as the mystery and chaos of the human mind.
Along with the discovery of Neptune came the discovery of anesthetics, hypnotism and the rise of the industrial state. The latter is why most authors attribute such political ideas as nationalism and communism to Neptune. The idea in both philosophies is that the individual needs and desires are unimportant in the light of the collective; that no one can prosper unless everyone prospers, and that individual achievement is unimportant compared to the advancement of society.
It takes almost 165 years to visit all 12 signs, and spends about 14 years in each sign. Neptune has an orbit that intersects with the erratic orbit of Pluto, and is sometimes the outermost planet of the Solar System. Like Uranus, the transits of Neptune from sign to sign are very important in political astrology; its action is more generational than it is personal.
Most modern astrologers consider Neptune as the ruler of Pisces. Traditionalists argue, as they do with Uranus, that Neptune cannot be forced into the scheme of rulership and exaltation. It was designed to perfectly match the Zodiac signs with the seven visible planets, which include the Sun and Moon.
Nevertheless, Neptune's association with Pisces, who tends to love the general rather than the particular, and who is more concerned with imagination than facts, is both obvious and certain.
Most human beings have a really difficult time tuning in to Neptune's astral influence. Neptune can inspire contradictions, confusion and disorder; most Virgo (Neptune's detriment) cannot abide any of them, unless they are more imaginative or "spiritual" in their personal work or interests.
Some astrologers and writers try to assign the exaltation of Neptune to Sagittarius, because it is the planet of idealism, but it's probably best to leave it out of that scheme, which was designed as part of a closed system based on Sacred Geometry.
If you are in the camp that assigns exaltation to Sagittarius, then you would also peg Neptune as fallen in Gemini. As evidence you might offer the idea that Gemini's imaginations can get them in trouble, but that generalization is really unkind to the Geminis who have a good relationship with this mystical planet.
When close to one of the personal planets, it can cause that planet to become a little less personal. For instance, Neptune conjunct Mercury in a birth horoscope often shows someone who quickly absorbs information from their environment, manages to be good at meditation or other therapeutic mental practices, or is highly imaginative. It also shows a person who will quickly adapt the style of dress, habits and even the verbal accent of those around them.
Neptune focuses on imagination, fantasy and idealism. These are three of the defining traits often associated with the watery world of Neptune.
When well connected with the other planets in the birth horoscope, Neptune can indicate an individual who is very sensitive, even psychic. We could say that Neptune is the planet of New-Age ideas, which are basically collections of different mystical traditions that are dissolved into one another, like raindrops falling on the sea.
Neptune is better known for its negative traits than its positive ones, probably because it doesn't fit well into the needs of the individual in today's economically-based society.
Some of these characteristics are a lack of discipline, an overactive imagination, laziness and a lack of concern for practical matters. If you want to use everyday language, you could call Neptune the "whatever" planet and baffle many highly trained astrologers with your observations.
Neptune is also the planet most closely associated with recreational drug use and alcoholism as a means of escape from facts and reality.
Because Neptune is more concerned with the collective than the individual, it's been observed that people who are strongly influenced by this planet are more likely to get wrapped up in social and political movements than personal idealism. Neptune is considered to be the planet of terrorism and fanaticism by many. In fact, Osama Bin Laden was born under the influence of this planet with the sun sign of Pisces.
In relationship astrology, Neptune can often represent submission and abandon. It can also represent a tendency to get wrapped up in others' dramas. When two people with strong Neptune influences get together, they often fall into a pattern in which responsibilities and obligations take a back seat to their emotional experience of the relationship, and truth becomes less important than a good story.
Many people with a powerful Neptune, unless they are absorbed in a scientific or spiritual pursuit, have problems with boundaries that make it difficult for them to pursue their own self-interest. But for people in creative professions or who manage to make their way in the world by pursuing their personal ideals, Neptune can be both a muse and a blessing. The "Law of Attraction" works wonderfully for those who can tune into Neptune's magic.