# Homework Help: Longitude problem on a Terrestrial Sphere

1. Mar 11, 2013

### Equilibrium

1. The problem statement, all variables and given/known data
How far apart (in miles) are 2 points on the equator if their longitudes differ by 1 degree?
The correct answer is 69.8 miles, i'm not sure if typo

2. Relevant equations
$$S=r\theta$$
radius of earth = 3959 miles

3. The attempt at a solution
$$\theta = 1\deg*\frac{\pi}{180}$$
$$S=3959*\frac{\pi}{180}$$
$$S = 69.1 miles$$

2. Mar 11, 2013

### Curious3141

Nothing wrong with your working, except that you should be more clear that you're starting by converting theta into radian measure. But your answer is right.

The difference could be because of the value you're supposed to use for the earth's equatorial (great circle) radius. Are you given a value you're supposed to use?

The value you quoted looks quite OK, but google's is slightly different: 3 963.1676 miles, and yields a slightly different answer (69.2mi, still closer to yours than the expected one).

3. Mar 12, 2013

### Equilibrium

thanks for verifying