The position of a heavenly body on the celestial sphere can be completely specified by A. Its altitude and azimuth B. Its declination and hour angle C. Its declination and right ascension D. All the above

Its altitude and azimuth
Its declination and hour angle
Its declination and right ascension
All the above

The correct answer is D. All of the above.

The altitude of a heavenly body is its angle above the horizon, measured from the observer’s zenith. The azimuth of a heavenly body is its angle from due north, measured from the observer’s meridian. The declination of a heavenly body is its angle north or south of the celestial equator. The right ascension of a heavenly body is its angle eastward from the vernal equinox, measured along the celestial equator.

All four of these quantities are necessary to specify the position of a heavenly body on the celestial sphere. For example, the Sun has an altitude of about 90 degrees at noon on the day of the summer solstice, an azimuth of due south, a declination of about 23.5 degrees north, and a right ascension of about 18 hours.

The altitude and azimuth of a heavenly body depend on the observer’s location on Earth. The declination and right ascension of a heavenly body are independent of the observer’s location on Earth.