On 1 October you determine the zone time of evening twilight will be 1835. Your DR position will be LAT 27°18.0'N, LONG 48°52.0'W. Considering their magnitude and location, which group of three stars are best suited to be used in obtaining a fix at star time?
• Star identification and brightness (magnitude) when selecting navigation stars • Altitude and azimuth spread for a three-star fix near evening twilight • Relationship between observer’s latitude and star declination for comfortable sight altitudes (20°–70°)
• Based on your DR latitude 27°N, which stars in each group are likely to have suitable declinations so their altitudes won’t be too low or too close to the zenith? • Which group gives you the best spread in azimuth (ideally 60°–120° apart around the horizon) instead of stars that are bunched together in nearly the same direction? • At evening twilight in early October in the western Atlantic, which stars are well placed above the horizon and not too close to the Sun’s bearing?
• Verify which option has three reasonably bright stars (1st or 2nd magnitude) that are commonly used as navigation stars • Check which group gives a good azimuth spread (not all in the same quadrant of the sky) for a strong three‑line fix • Eliminate any set where one or more stars would likely be too low (<15°) or too high (>75°) in altitude at your DR position and time of year
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