There is no specific planet that represents a black cat in astrology or any other cultural tradition. The association of planets with animals is not a standard practice in any recognized astrological system.
However, some might associate black cats with the planet Saturn due to its association with darkness, mystery, and misfortune, which are often attributed to black cats in folklore.
It's important to remember that these associations are largely based on popular beliefs and interpretations, and not on any scientific or astrological basis.
