Chart Navigation & Plotting · Piloting — Bobbing a Light
At night you sight a light on the horizon, then it disappears when you lower your eye and reappears when you raise it. What does 'bobbing a light' confirm?
- AYou are at the light's geographic range, so the distance off equals its computed geographic range✓ Correct
- BThe light is operating at reduced intensity
- CYou are inside the light's nominal range only
- DThe light is a sector light at the edge of its red sector
Explanation
If raising and lowering the eye makes the light appear and disappear, you are at its geographic range. Computing the geographic range for the charted height of the light and your height of eye then gives a useful distance off.
Authority: Bowditch (Pub. No. 9), bobbing a light
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