Why is declination important to mariners?

• A. Declination is equivalent to the altitude of a celestial body
• B. Declination measures the distance to the horizon
• C. Declination indicates azimuth of the sun
• D. Declination tells time of day

Answer: (A)

Declination is the angular distance of a celestial body north or south of the celestial equator. This north–south position on the sky is what mariners rely on to relate a body's location to their own latitude. When a body crosses the local meridian, its altitude above the horizon is determined by how far north or south it is (its declination) relative to the observer’s latitude. In practice, knowing the sun’s or a star’s declination allows you to predict its maximum height in the sky and, from measured altitudes, compute your latitude or check sight reductions. The other statements mix up what declination measures: altitude is the angle above the horizon, azimuth is the compass direction, and time of day is governed by hour angle and the body’s declination rather than declination alone.