# How much of the electromagnetic spectrum does Sun emits?

I'm wondering how much of the electromagnetic spectrum does the sun emits! It obviously emits visible light, but what about the other?
Does the sun emits radio waves? If that's the case why them do not interact with the radio waves on earth?

• – honeste_vivere Jun 23 '17 at 17:14
• – user122423 Jun 23 '17 at 17:33

Attached is an image from the internet. The suns temperature is around 5800 degrees Kelvin at the surface. The sun is fairly well represented by a blackbody. The blackbody equations were used to generate the curves shown on this image. The curve closest to that of the sun shows a peak near the color yellow as expected. Most of the sun's energy (area under curve) is generated in the infrared wavelength region. The curve decreases as shown so the intensity of radio waves (not shown on image) is very small. The curve essentially goes to extremely long wavelengths but with ever decreasing strength. So yes the sun emits radio waves of every frequency. In projects I've worked on in the past some missiles communicated to ground via radio frequencies. It was determined to be important that antenna was not facing the sun due to interference from suns radio waves. So at least above the atmosphere the small intensifies of radio waves was enough to cause interference. I can't disclose the applicable wave bands.

The Sun is often approximated as a "blackbody". A blackbody whose surface is of temperature $T$ on the Kelvin scale emits radiation of angular frequency $\omega$ with an intensity proportional to $\dfrac{x^3}{e^x-1}$ with $x:=\dfrac{\hbar\omega}{k_B T}$, where $\hbar$ is the Dirac constant and $k_B$ is the Boltzmann constant. This intensity measure is by power; by photon count, we drop one power of $x$. If you work in terms of wavelength, $x=\dfrac{2\pi\hbar c}{k_BT\lambda}$.

On this model, any frequency can be emitted to some extent, so you have to decide what's a non-negligible emission. (For example, is an intensity $1,000$ times less than the peak negligible?) Animal eyes evolved to exploit sunlight for vision, and both infrared and ultraviolet (which are slightly outside human vision) are a large enough part of the Sun's output for some animals to use it. However, radio waves (which have much lower frequencies than infrared) are essentially absent, as are X-rays (which have much higher frequencies than ultraviolet).

The analysis of black-body radiation of the Sun's surface was done in previous answers. Hovever, this is not the only mechanism responsible for. Sun's radiation and the surface is not the only region emitting. Actually the Sun is the strongest radio source in the sky. And it has strong xray emission too. Images of the sun in xray and radio waves regions can be found online.

## protected by Qmechanic♦Jun 23 '17 at 19:06

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