The correct answer is B) Polar distance. In the celestial equator system of coordinates, the polar distance is equivalent to the colatitude in the Earth system of coordinates. The polar distance is the angular distance between a celestial object and the celestial pole, which corresponds to the colatitude, which is the angular distance between a point on the Earth's surface and the North or South Pole. The other options are incorrect because: A) Zenith distance is the angular distance between a celestial object and the observer's zenith, not the celestial pole; C) Coaltitude is the complement of the altitude, not the colatitude; and D) Declination is the celestial equivalent of latitude, not the colatitude.