Answer:
420 miles.
Step-by-step explanation:
You would have to be infinitely far away from a sphere in order to see exactly 50% of its surface all at the same moment. Using simple geometry, you can prove that an observer that is a distance d away from the surface of a sphere with radius R can only see a percent area A of the sphere's surface as given by the equation:
A = 50%/(1+R/d)
Where A is the area seen,
R is the earth's radius 4000 miles
And D is the distance above the earth 200 miles
50% = 0.5 in fraction
Substituting values we have
A = 0.5(1 + 4000/200)
A = 0.5(1 + 20) = 0.5 x 21
A = 10.5%
10.5% of 4000 miles = 420 miles.
