Which statement best defines a sky wave?

• A. A wave bounced off the ionosphere.
• B. It travels along the ground.
• C. It travels through space and avoids the atmosphere.
• D. It is not used for communications.

Answer: (B)

Sky waves travel by being directed upward and then reflected or refracted back to Earth by the ionosphere, allowing the signal to cover distances beyond the horizon. This reflection is what enables long-range HF communications, so the best description is that a sky wave is bounced off the ionosphere.

Ground waves stay along the Earth's surface, interacting with the ground and atmosphere, and do not rely on the ionosphere. Space or line-of-sight waves travel through space and reach receivers without ionospheric reflection, typical for VHF/UHF bands and satellite links. The idea that sky waves aren’t used for communications isn’t accurate, since they are a primary method for long-distance radio, especially on the HF bands.