The [[Ionosphere]] is a region of Earth's upper atmosphere where sunlight knocks electrons loose, creating charged particles (ions and free electrons).

If you want the practical version: it is one of the big reasons radio range changes between day and night.

## Why it exists
UV and X-ray energy from the [[Sun]] ionizes parts of the atmosphere.

During daylight, ionization is stronger. At night, some layers weaken, especially the [[D Layer]].

## Why radio people care
- Some radio waves get absorbed.
- Some bend or reflect back toward Earth.
- Some pass through into space.

That means the ionosphere can change how far a signal travels, how noisy it sounds, and whether long-distance reception works at all.

For [[AM]] specifically, the daytime D layer absorbs more signal, while nighttime conditions allow more skywave propagation, so stations can be heard much farther away.

It also affects some [[Satellite]] and navigation signals by adding small delays and distortion that receivers have to correct for.

## See also
- [[D Layer]]
- [[AM]]
- [[FM]]
- [[Electromagnetic Spectrum]]
- [[Electromagnetic Radiation]]
- [[Sun]]