VHF (Very High Frequency) waves are highly energetic (remember lots of short waves). They travel in straight lines through space but are easily blocked by the earth’s curvature. We refer to them as line-of-sight transmissions and they behave very much as light itself.
VHF is perfect for communicating with aircraft, or even spacecraft! So it only seems fitting we think of VHF as ‘skywaves’.
Other types of skywaves are UHF (Ultra High Frequency) and SHF (Super High Frequency).
If you were flying low, with a mountain blocking the ‘line-of-sight’ between you and the antenna it would be expected you wouldn’t receive the signal.