1. See upright. 1. horizontal. 1  being in a position or direction perpendicular to the plane of the horizon; upright; plumb. 2  of, pertaining to, or situated at the vertex. 3  Anatomyof or pertaining to the cranial vertex.
Last Updated: Radio wave, wave from the portion of the electromagnetic spectrum at lower frequencies than microwaves. The wavelengths of radio waves range from thousands of metres to 30 cm. These correspond to frequencies as low as 3 Hz and as high as 1 gigahertz (109 Hz).
Radio waves are photons like light. When photons pass through regions where their speed changes they tend to bend, from their original trajectory. The same phenomenon occurs when you put a spoon in water. you will see it bend. The photons reach the ionosphere where the refraction rate is different, so they bend.