How Far Can You See a Light? Assuming the Earth is not Flat....

Описание: The visibility of a light at sea depends on the three main factors, and you can use this information to navigate a ship or to pass an exam.

In this video we discuss Geographic Range, Nominal Range, and Luminous Range of lights, including how to use that information at sea.

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0:00 Introduction
0:28 Luminous Range
0:41 Geographic Range
1:13 What is the Visibility of the Light?
1:50 In-Depth Look at the Problem for Exams or Navigation
5:37 Conclusion and Bottom Line


Here are a few USCG exam questions for extra practice:

1. What is the approximate geographic visibility of an object with a height above the water of 70 feet, for an observer with a height of eye of 65 feet?
a. 16.8 nm
b. 19.0 nm - correct
c. 20.6 nm
d. 22.4 nm


2. What is the approximate geographic range of Shinnecock Light, NY, if your height of eye is 24 feet (7.3 meters)?
a. 8.7 nm
b. 9.9 nm
c. 14.4 nm
d. 15.9 nm - correct

3. The Light List shows that a navigational light has a nominal range of 6 miles and a height above water of 18 feet (5.5 meters). Your height of eye is 40 feet (12.2 meters) and the visibility is 27.0 miles. At which approximate range will you first sight the light?
a. 5.6 miles
b. 6.4 miles
c. 9.8 miles - correct
d. 12.1 miles


Here is the link to Bowditch https://msi.nga.mil/Publications/APN

Here is the link to the Light List (CG exam - beware of large file sizes): https://www.dco.uscg.mil/Portals/9/NM...