Earth emits long wave radiation because it is much cooler than the Sun. All objects emit radiation, but the wavelength of the radiation depends on the temperature of the object. The Sun is very hot, so it emits short wave radiation, which includes visible light. Earth is much cooler, so it emits long wave radiation, which is infrared radiation.

Infrared radiation is a type of electromagnetic radiation that has a longer wavelength than visible light. It is also known as thermal radiation, because it is emitted by all objects that have a temperature above absolute zero.

The Earth's atmosphere is transparent to most short wave radiation, so the Sun's short wave radiation can pass through the atmosphere and reach the Earth's surface. However, the atmosphere is not transparent to long wave radiation. Greenhouse gases in the atmosphere, such as water vapor, carbon dioxide, and methane, absorb long wave radiation and re-emit it in all directions. This is why the Earth's surface is warmer than it would be if there were no greenhouse gases in the atmosphere.

Some of the long wave radiation emitted by the Earth's surface is absorbed by the atmosphere and then re-emitted back to the Earth's surface. This is known as the greenhouse effect. The greenhouse effect is necessary to maintain a livable temperature on Earth. However, too much greenhouse gas in the atmosphere can cause global warming.

To summarize, the Earth emits long wave radiation because it is much cooler than the Sun. The Earth's atmosphere is transparent to most short wave radiation, but it absorbs and re-emits long wave radiation. This is known as the greenhouse effect, and it is necessary to maintain a livable temperature on Earth.

Dr Murtadha Shukur thank you for your contribution to the discussion

Earth's surface and atmosphere absorbs solar radiation and re-radiates it as long wave radiation. We feel this long wave radiation as heat. Energy radiated from Earth's surface as heat, or infrared radiation, is absorbed and re-radiated by greenhouse gases, impeding the loss of heat from our atmosphere to space. The Earth radiates energy at wavelengths much longer than the Sun because it is colder. Part of this long wave radiation is absorbed by greenhouse gases which then radiate energy into all directions, including downwards and thereby trapping heat in the atmosphere. Heat resulting from the absorption of incoming shortwave radiation is emitted as long wave radiation. Radiation from the warmed upper atmosphere, along with a small amount from the Earth's surface, radiates out to space. When Earth absorbs sunlight, it heats up. The heat, or "outgoing long wave radiation," radiates back into space. Satellites measure this radiation as it leaves the top of Earth's atmosphere. The hotter a place is, the more energy it radiates. In most cases, the net long wave radiation is incoming during the daylight hours, and outgoing during the night hours. The long wave radiation method included in the meteorological model is only necessary when energy balance methods are used for evapotranspiration or snowmelt. The Sun also emits at longer wavelengths, in the infrared, microwave, and radio. Our Sun emits light at progressively shorter wavelengths, too: the ultraviolet, X-ray, and even gamma-ray parts of the spectrum.Some of the solar energy (radiation) passes through the Earth's atmosphere and hits the Earth's surface Earth's surface absorbs the energy and warms up. Some of the radiation that hits the earth's surface or atmosphere is reflected back into space. The Earth absorbs most of the energy reaching its surface, a small fraction is reflected. In total approximately 70% of incoming radiation is absorbed by the atmosphere and the Earth's surface while around 30% is reflected back to space and does not heat the surface.