Question 10 AB01 - Able Seafarer

The Correct Answer is B **Explanation of why option B is correct:** Geographic range (or Nominal Range) is a theoretical calculation used primarily in lighthouse and nautical navigation contexts to determine the maximum distance a light source can be seen, *before* considering atmospheric limitations like fog or rain. This distance is calculated geometrically, based on two factors: the height of the light source above the water, and the height of the observer's eye above the water. Since light travels in a straight line, the curvature of the Earth eventually obstructs the light from view. Therefore, the geographic range assumes **permitting visibility conditions** (i.e., perfect or ideal atmospheric clarity, $10$ nautical miles visibility or greater) and is **limited only by the curvature of the Earth**. **Explanation of why other options are incorrect:** * **A) Existing visibility conditions, limited only by the curvature of the Earth:** "Existing visibility conditions" refer to the actual, current atmospheric state (e.g., fog, haze, clear). If existing conditions are poor, the light's *luminous range* (the distance limited by the intensity of the light under prevailing atmospheric conditions) will be much shorter than its geographic range. Geographic range, by definition, ignores existing poor atmospheric conditions and assumes ideal visibility. * **C) Existing visibility conditions, limited only by the intensity of the light:** This option describes Luminous Range, not Geographic Range. Luminous Range is determined by how far the light intensity can penetrate the existing atmosphere. Geographic Range is determined solely by the horizon/curvature of the Earth, assuming perfect visibility. * **D) Permitting visibility conditions, limited only by interference from background lighting:** Background lighting (like city lights) can affect an observer's ability to spot a navigational aid, but it is not the primary limiting factor for defining the maximum *geometric* range. Geographic range is fundamentally limited by the Earth's curvature, regardless of background interference.