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Desde la situación 51° 37,8' S, 173° 11,1' W, vamos a observar un astro de coordenadas: horario del lugar = 104° 05,8', declinación = 19° 38,4' S. ¿En qué acimut náutico lo veremos?From position 51° 37.8' S, 173° 11.1' W, we observe a body with local hour angle = 104° 05.8' and declination = 19° 38.4' S. At what nautical (circular) azimuth will we see it?
Show the answer
Correct answer: c) 247°
Why it is correct
Since hL = 104º 05.8′ (< 180º), the meridian angle is P = 104º 05.8′ W. Applying tan Z = sin P / (cos l tan d − sin l cos P) with negative l and d gives Z = N 113.0º W, which as a circular azimuth is 360º − 113.0º = 247º.
Why the others are not
- a) Takes the supplement in the eastern semicircle (068º).
- b) Leaves the quadrantal angle (113º) as if P were East instead of West.
- d) Fails to switch quadrants when the denominator is negative (360º − 67º = 293º).
How to work it out in the exam
- If 0º < hL < 180º, the body is west and its circular azimuth lies between 180º and 360º.
Where this question comes from
- Junta de Andalucía · 2023 · 1ª convocatoria · CY Módulo de navegación · question 14 Official paper · Official answer key
Pending instructor review. Machine translation, not reviewed.