The name thermosphere is taken from the Greek word "thermos" which means 'heat'. This layer has high temperatures because it absorbs X-rays and extreme ultraviolet radiation from the Sun. Even though it has temperatures of 2,000 °C (3,360 °F), the density of the thermosphere is so low that it doesn't feel hot. The absorbed ionizing radiation also creates the ionosphere. Shortwave radio waves can bounce off the Kennelly-Heaviside layer (ionosphere) and go to distant parts of the Earth. This layer is very helpful in radio communication.