On 3 December evening twilight for your vessel will occur at 1901 zone time. Your vessel's DR position will be LAT 24°18.5' S, LONG 110°30.6' W. Considering their magnitude and location, what are the three stars best suited to observe for a fix at star time?
• Star selection for a three‑star fix (good azimuth spread: roughly 60°–120° between stars) • Relationship between observer’s latitude and star declination (high stars vs. low-altitude stars) • Approximate local hour angle (LHA) / bearing of stars near evening twilight at that date, longitude, and in the Southern Hemisphere
• Which stars in the options are well known, bright navigational stars that are normally available around early evening in early December for a position near 24° S, 110° W? • From 24° S, do you want mostly northern stars, mostly southern stars, or a mix? Think about how star declination affects altitude from your latitude. • Look at each trio and imagine their bearings on the horizon – which set would give you good separation in azimuth (not all bunched up in the same part of the sky)?
• Check which stars are southern vs. northern and which would be too low or not visible from about 24° S latitude. • Verify which option gives you stars spread over different bearings (e.g., one to the west, one to the east, one to the south or north) instead of all in roughly the same direction. • Confirm that each chosen star would be reasonably bright and above 15° altitude at evening twilight near your DR position and date.
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