🔍 Key Concepts

• Nominal range vs geographic range of a light (which one limits visibility in clear weather?) • Effect of earth’s curvature and height of eye on how far you can see a light • Using the lesser of charted/nominal range and geographic range to find when you lose sight

💭 Think About

• Think about what “clear weather” implies about the limiting factor: is the light’s brightness the limit, or the curvature of the earth? • Recall or look up the formula or table that gives geographic range based on the height of the light and the observer’s height of eye; which distance does that give you here? • Once you know the geographic range, compare it to the charted (nominal) range of 20 nm—what does that tell you about when you actually lose sight of the light?

✅ Before You Answer

• Be sure you are using geographic range (not luminous/nominal range) for a clear-weather visibility limit problem. • Confirm which distance is smaller: geographic range or 20 nm; that smaller value controls when you lose sight. • Verify that your computed/selected distance matches a realistic distance to the horizon for typical heights of eye and light—eliminate any option that seems too close or too far for a 20 nm nominal light.