The sun is the star at the center of our solar system that produces a vast amount of light and heat. It is also a source of energy that powers our planet and other celestial bodies in the solar system through nuclear fusion. This process combines two atoms of hydrogen to form one atom of helium and releases a tremendous amount of electromagnetic radiation, including visible light, ultraviolet radiation, and infrared radiation.
The visible portion of the Sun’s radiation is called sunlight and is used to provide light for photosynthesis by plants and to warm the Earth’s atmosphere. In addition to the visible spectrum, the Sun also emits a range of other electromagnetic radiation, including X-rays and extreme UV, both of which are absorbed by the atmosphere.
Solar irradiance is measured by space-based satellite instruments and by ground-based observing systems such as weather radars, sunspot observatories, and sunspot number calculations. It varies with the time of day, with seasons, and with the presence or absence of clouds. Longer-term variations in irradiance can be estimated with a variety of techniques, such as solar constant reconstructions using the 11-year sunspot solar cycle and with cosmogenic radionuclides for going back 10,000 years or more.
The Sun’s total power output is known as its luminosity and is estimated to be 3.827