What is meant by right ascension and declination of a star, how does this differ from altitude and azimuth?
Right ascension and declination are what astronomers use to precisely locate objects on a celestial map, and are equivalent to the imaginary lines of longitude and latitude used in maps of the earth. Although it is obvious that all of the stars lie at different distances from the earth, it is also convenient to think of the sky as a fixed sphere with the earth at the centre. Just as the earth has a north pole, south pole, and equator, so does the sky. The altitude of a point is its angular distance above or below the horizon. It can range from -90 degrees to +90 degrees with the altitude of the zenith being +90 degrees and the altitude of the nadir being -90 degrees. The altitude of any point on the horizon is 0 degrees. The complement to the altitude is the zenith distance, which is sometimes used instead of the altitude. The zenith distance is the angular distance between the zenith and the point. The zenith distance added to the altitude is always 90 degrees. The azimuth of a point
