Hover or tap underlined Spanish terms to see their translation and exam tip.
Sabiendo que el 26 de abril de 2025 se toma una altura instrumental de la estrella Sirius de 20º31,0´, que el observador se encuentra a una altura de 8,2 metros sobre el nivel del mar y que el error de índice del sextante es de 0,1´ (-), se pide calcular la altura verdadera de dicho astro.On 26 April 2025 the sextant altitude of the star Sirius is 20º 31.0', height of eye is 8.2 m above sea level, and the sextant index error is 0.1' (-). Calculate the star's true altitude.
Show the answer
Correct answer: c) 20° 23.2'.
Why it is correct
For a star, only index error, dip, and refraction apply (no semi-diameter or parallax). With ai = 20º 31.0′, Ci = −0.1′, dip for 8.2 m (−5.1′), and mean refraction at 20º 25′ (−2.6′), av = 20º 31.0′ − 7.8′ = 20º 23.2′.
Why the others are not
- a) Subtracts the dip of the horizon twice.
- b) Subtracts 1′ too much in refraction or index error.
- d) Subtracts only 1.5′ of refraction instead of the 2.6′ required at 20º altitude.
How to work it out in the exam
- For stars, both dip (−5.1′) and refraction (−2.6′) subtract.
Where this question comes from
- Ministerio de Transportes (Madrid) · 2025 · Convocatoria de abril · CY Test 1 · question 14 Official paper · Official answer key
- Ministerio de Transportes (Madrid) · 2025 · Convocatoria de abril · CY Test 2 · question 15 Official paper · Official answer key
Pending instructor review. Machine translation, not reviewed.