How do electrons become excited in an atom

[Strafespar]

I was wondering why hot objects glow (such as a heated metal), what I found on wiki:
"Thermal radiation is energy emitted by matter as electromagnetic waves due to the pool of thermal energy that all matter possesses that has a temperature above absolute zero. Thermal radiation propagates without the presence of matter through the vacuum of space.[11]

Thermal radiation is a direct result of the random movements of atoms and molecules in matter. Since these atoms and molecules are composed of charged particles (protons and electrons), their movement results in the emission of electromagnetic radiation, which carries energy away from the surface"

Which makes sense for the most part, except the fact of why the objects spontaneously radiate energy..."their movement results in the emission of EM radiation..."<--why?

Thank you to all who reply!

 

[Drakkith]

When you shake a charge back and forth it causes the EM field to oscillate as well. These oscillations generate photons, aka EM radiation. It is important to note that anytime you accelerate a charged particle it will produce EM radiation. Since changing direction is acceleration, oscillations produce radiation. Another notable example is circular particle accelerators. As the particles are forced in a circular path by the magnetics, they release radiation. Once the speed of the particles reaches a certain point you cannot accelerate them any more as they lose the extra energy too fast by radiating it away.

 

[Strafespar]

Why exactly does it produce EM radiation? Does it have to do with preserving something, such as gauge invariance?