Don't really believe in astrology, but this is so accurate.
Pisces is the twelfth sign of the Zodiac, and governs the feet. Positive traits include idealism, wisdom, intuition, empathy, imagination, creativity, adaptability, compassion, and an uncanny connection to all that is spiritual and otherworldly (which makes for talent in magic); negative traits include being easily influenced by other people, gullibility, a lack of backbone, escapism, addictive personality, impracticality, emotional game-playing, delusion, and a total inability to say "no."
Slytherin
This is not the most natural of sun signs for a Slytherin to be born into, but it's not unheard of, and when it happens, the results are usually interesting. These Slytherins dream big. Because of their romantic streak and their need for mystery and glamour, their dreams are often the most dazzling of all. To put them into fruition, they either need to develop a pragmatic streak, or partner up with a practical wizard who will help midwife the dreams and keep them going. These Slytherins are loners or followers rather than leaders, but don't assume that they are doormats - they wouldn't be Slytherin if they didn't have some backbone. They will accomodate people to the best of their limits, but if those limits are pushed or violated, they will get angry - and they will remember. A Pisces never forgets a cut or a kindness. Ever. Slytherin Pisceans often delve into mysteries involving death and afterlife, for Pisces is naturally placed in the house of endings; Pisces wizards in House Slytherin will also be brilliant seers and potion brewers. Because these wizards are good with people and human psychology, they understand everybody around them; and because they are so quiet and unassuming, nobody notices that they are there. The wise Pisces in House Slytherin of course is aware of this, and uses it to advantage.
From http://www.spenecial.com/birdsofafeather/astrology.htm
Slytherin
This is not the most natural of sun signs for a Slytherin to be born into, but it's not unheard of, and when it happens, the results are usually interesting. These Slytherins dream big. Because of their romantic streak and their need for mystery and glamour, their dreams are often the most dazzling of all. To put them into fruition, they either need to develop a pragmatic streak, or partner up with a practical wizard who will help midwife the dreams and keep them going. These Slytherins are loners or followers rather than leaders, but don't assume that they are doormats - they wouldn't be Slytherin if they didn't have some backbone. They will accomodate people to the best of their limits, but if those limits are pushed or violated, they will get angry - and they will remember. A Pisces never forgets a cut or a kindness. Ever. Slytherin Pisceans often delve into mysteries involving death and afterlife, for Pisces is naturally placed in the house of endings; Pisces wizards in House Slytherin will also be brilliant seers and potion brewers. Because these wizards are good with people and human psychology, they understand everybody around them; and because they are so quiet and unassuming, nobody notices that they are there. The wise Pisces in House Slytherin of course is aware of this, and uses it to advantage.
From http://www.spenecial.com/birdsofafeather/astrology.htm