how tall to see land across water
A viewer 20 feet above the water looking at a lighthouse light 100 feet above the water, would be able to see it at a distance of 17.8 miles. Using the formula above: Square Root of 100 = 10 10 x 1.23 miles = 12.3 plus Square Root of 20 = 4.5 4.5 x 1.23 miles = 5.5 miles Total = 17.8 miles.