Hover or tap underlined Spanish terms to see their translation and exam tip.
Para un observador situado en Bilbao (43° 15,7′ N, 002° 57,2′ W), un astro con declinación 47º N:For an observer in Bilbao (43° 15.7′ N, 002° 57.2′ W), a celestial body with declination 47º N:
Show the answer
Correct answer: a) Has only a diurnal arc (remains above the horizon all day).
Why it is correct
A body is circumpolar (never sets, having only a diurnal arc) when its declination has the same name as the observer’s latitude and equals or exceeds the colatitude (δ ≥ 90° − φ). At Bilbao, colatitude is 90° − 43° 15.7′ = 46° 44.3′; since δ = 47° N > 46° 44.3′, the body stays above the horizon 24 hours a day.
Why the others are not
- b) It would both rise and set only if 0° < δ < 46° 44.3′ N.
- c) That would happen for South declinations between 0° and 46° 44.3′ S.
- d) It would have only a nocturnal arc if its declination were south of 46° 44.3′ S.
How to work it out in the exam
- Circumpolar body (δ ≥ 90° − φ, same name): at φ = 43° 15.7′ N with δ = 47° N, it has only a diurnal arc.
Where this question comes from
- Junta de Andalucía · 2022 · 3ª convocatoria · CY Módulo de navegación · question 5 Official paper · Official answer key
Pending instructor review. Machine translation, not reviewed.