You are on course 209°T. In order to check the longitude of your vessel, you should observe a celestial body on which bearing?

Correct Answer: Option D — 270°

To determine longitude via celestial observation, the body must be near the prime vertical, where its altitude changes most rapidly. A body bearing 270° (due west) or 090° (due east) provides the most accurate longitude line, as the change in altitude is directly related to time.