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Electromagnetic radiation is a form of energy that is all around us and takes many forms, such as radio waves, microwaves, X-rays, and gamma rays. Sunlight is also a type of electromagnetic radiation that is visible to the human eye. This spectrum is vast, ranging from waves with extremely low energy, like radio waves, to highly energetic gamma rays. The Sun, a massive nuclear furnace, emits a broad array of electromagnetic radiation, which includes not only visible light that we can see but also ultraviolet (UV) rays which can tan or burn our skin, and infrared (IR) radiation which is felt as heat. The Earth, on the other hand, with its much cooler temperature, does not emit UV or visible light naturally, but rather it radiates energy primarily in the IR part of the spectrum. In essence, differences in the types of electromagnetic radiation emitted from celestial bodies like the Sun and Earth are directly tied to their temperatures.

The temperature of an object determines which wavelengths of radiation it emits most strongly, a concept described by the black-body radiation law. For instance, the Sun, with its surface temperature of approximately 5,500 degrees Celsius, is an efficient emitter of visible light, as evidenced by the bright daylight we experience. A part of the sun's emission spectrum also falls into the ultraviolet range which can cause sunburn, emphasizing the need for UV-protection. Conversely, the Earth with its comparatively modest average surface temperature around 15 degrees Celsius emits most of its energy in the infrared range — radiation that is invisible to us but can be detected by its warmth or with special instruments. This difference in the peak wavelength of emissions between the Sun and Earth is primarily due to their varied surface temperatures, governed by Planck's law of black-body radiation.

The intensity of radiation can be thought of as the amount of energy radiated per square meter of an object's surface per second. The Sun, being much larger and immensely hotter than Earth, naturally emits radiation with a vast intensity. This is due to the fact that intensity is directly proportional to the fourth power of the temperature, as described by the Stefan-Boltzmann law. Thus, even a small increase in temperature can result in a large increase in the amount of radiation emitted. Furthermore, the large size of the Sun means that it has a greater area from which to radiate energy, further increasing its total output compared to Earth. Understanding the intensity differences is crucial, not just in comparing Earth to the Sun, but also in studying the energy balance within Earth's own atmosphere and how it affects our climate and weather patterns.