*Question E3A01:
What is the approximate maximum separation measured along the surface of the Earth between two stations communicating by EME?*  

*Correct Answer is  D: 12,000 miles, if the moon is “visible” by both stations*  

### AI Response: (may contain errors)  

To understand the maximum separation between two stations communicating via Earth-Moon-Earth (EME) or "moonbounce," we need to consider the geometry of the Earth and the Moon.

### Explanation:

1. **Correct Answer: D: 12,000 miles, if the moon is “visible” by both stations**

   - **Reasoning**: EME communication relies on both stations having a line of sight to the Moon. The maximum separation occurs when both stations are on opposite sides of the Earth, but still able to "see" the Moon. This typically allows for a maximum separation of about 12,000 miles along the Earth's surface. This is because the Moon can be visible to stations that are up to approximately 6,000 miles apart from the sub-lunar point (the point on Earth directly under the Moon).

2. **Why Other Choices Are Incorrect:**

   - **A: 2,000 miles, if the moon is at perigee**
     - **Incorrect**: The Moon's distance from Earth (perigee or apogee) does not significantly affect the maximum separation between stations for EME. The key factor is the visibility of the Moon from both locations, not its distance from Earth.

   - **B: 2,000 miles, if the moon is at apogee**
     - **Incorrect**: Similar to choice A, the Moon's apogee does not limit the separation to 2,000 miles. The separation is determined by the visibility of the Moon, not its distance.

   - **C: 5,000 miles, if the moon is at perigee**
     - **Incorrect**: Again, the Moon's perigee does not limit the separation to 5,000 miles. The maximum separation is about 12,000 miles when both stations can see the Moon.

### Key Points:

- **Visibility**: The critical factor for EME communication is that both stations must have the Moon in their line of sight.
- **Maximum Separation**: Approximately 12,000 miles is the maximum separation when both stations can see the Moon, regardless of the Moon's distance from Earth (perigee or apogee).

This understanding helps in determining the feasibility of EME communication between two stations based on their geographic locations and the Moon's position.