*Question G3A11:
How long does it take a coronal mass ejection to affect radio propagation on Earth?*  

*Correct Answer is  D: 15 hours to several days*  

### AI Response: (may contain errors)  

To understand how long it takes a coronal mass ejection (CME) to affect radio propagation on Earth, we need to consider the nature of CMEs and their travel time through space.

1. **Correct Answer: 15 hours to several days**
   - A coronal mass ejection is a significant release of plasma and magnetic field from the solar corona. When a CME is ejected, it travels through space and can take anywhere from about 15 hours to several days to reach Earth, depending on its speed and the distance it has to travel. 
   - Typical speeds of CMEs can range from 250 km/s to over 3000 km/s. At these speeds, the time taken to reach Earth varies significantly.

2. **Why the other choices are incorrect:**
   - **A: 28 days**: This is incorrect because it takes much less time for a CME to reach Earth. The 28-day period is more related to the solar rotation period, which is not relevant to the travel time of a CME.
   - **B: 14 days**: Similar to the 28 days, 14 days is too long for a CME to affect radio propagation. Most CMEs reach Earth in a matter of hours to days, not weeks.
   - **C: 4 to 8 minutes**: This is incorrect as well. While solar flares can affect radio propagation almost instantaneously (in about 8 minutes, the time it takes light to travel from the Sun to Earth), CMEs take much longer due to their larger mass and slower speed.

3. **Useful Information:**
   - CMEs can travel at varying speeds, and their impact on radio propagation can be predicted based on their speed. A rough rule of thumb is:
     - If a CME travels at about 1000 km/s, it would take approximately 15 to 20 hours to reach Earth.
     - Faster CMEs can arrive sooner, while slower ones can take several days.

In summary, the correct answer reflects the actual travel time of CMEs to Earth, while the other options do not accurately represent this phenomenon.