What is "parallactic angle"

In spherical astronomy, the parallactic angle is the angle between the great circle through a celestial object and the zenith, and the hour circle of the object. It is usually denoted q. In the triangle zenith—object—celestial pole, the parallactic angle will be the angle at the celestial object. Despite its name, this angle is unrelated with parallax. The parallactic angle is zero when the object crosses the meridian.