To pretty much everything you stated in your question, "no".
That convection requires a medium is not the main difference, it is simply the most obvious aspect of what is a fundamentally different mechanism for transferring energy. Convection is the transfer of energy by movement of a medium, whereas radiation is the transfer of energy by, well, thermal radiation. Conduction also requires a medium, but, again, it is a fundamentally different mechanism than either convection or radiation; in this case it is the transfer of energy through a medium.
Unfortunately, analogies are hard but if you can visualize the particles involved, it would help. Picture the red hot iron you mentioned. On a molecular level, the material is emitting lots and lots of photons (hence why it is glowing red). The creation of these photons takes energy; energy from the heat of the iron. These photons leave the iron, pass through the environment, and eventually collide with some other object where they are absorbed and deposit their energy. This is radiative heat transfer. If that energy is deposited on your retina or a CCD (like in a digital camera), an image forms over time. This is how infrared goggles work and they would work equally well in high vacuum as here on earth.
In conduction, the next simplest example, there is no generation of photons (physics nerds forgive me for the sake of simplicity). The individual atoms in the object are vibrating with heat energy. As each atom gains energy from its more energetic neighbors, so it gives up energy to its less energetic ones. Over time, the heat "travels" through the object.
In convection, the molecules of gas near the object gain energy, like in the conduction case, but those same molecules that gained energy then travel through the environment to some other location where they then give off their heat energy.
In summary:
- radiation = generated and absorbed photons
- conduction = molecules exciting their neighbors successively
- convection = molecules heated like in conduction, but then move to another location
So I understand the electromagnetic spectrum -- electromagnetic
radiation is mediated by photons
Briefly, electromagnetic radiation is due to real (observable) photons; electric and magnetic force are due to virtual photon exchange.
The macroscopic electromagnetic wave phenomena we observe are due to an almost unimaginable number of photons, electromagnetic "quanta", coherently adding together.
This is where I get lost; I can't visualize how it works.
This topic is not something that one "groks" overnight or, if you're like me (an EE), over some period of years. It's a continuous process.
Just today, while driving to Lowe's, something I had been thinking a long time about in quantum field theory suddenly became very clear.
The fact is, no matter how many classes you take or books you read, much of the material must, like a great chili, "stew" for awhile before it's ready.
Best Answer
It is a matter of confusing terminology , at the present times when so much differentiation has happened in physics related scientific disciplines.
Radiation was a general terminology assigned to transfer of energy radially, to start with with waves: acoustic waves, waves in water.
Then came Maxwell's equations and the discovery of electromagnetic waves, which emitted energy in waves from a point source radially. ( in the beginning they thought ether existed on which the waves transferred the energy, but that is another story)
Then came the experimental discovery of nuclear energy, which emits energy radially from point sources, and is invisible to the eye . It was called radiation and the elements emitting it were called radioactive. This is where the split happens, between the strict meaning in physics of radiative transfer of energy through waves, and the nuclear community vocabulary: radiation is any ( note not particularly wave) form of radially emitted energy from a source/nucleus.
This last meaning has dominated the vocabulary of nuclear related disciplines, like health physics, and certainly the news. Certainly it is not wrong, it is just a double use of the term.
In nuclear physics you can call radiation gamma rays and be true to the wave definition, because a gamma is an electromagnetic wave that is emitted radially from the source. Alpha (helium nuclei), beta+/- ( positrons/electrons) , higher nuclear fragments from heavy nuclei breakups will also be called radiation for health physics purposes too, with the second meaning of the term.
Electromagnetic radiation has a spectrum of frequencies, beginning from infrared to gamma ray energies. At low energy, i.e. in the infrared regime, you know electromagnetic radiation as radio waves, microwaves or "heat radiation". At intermediate energies it makes up the visible light. At even higher energies, it can be ionizing, if the energy of the radiation is higher than the energy with which the electrons are bound in an atom. These range from X-Rays to gamma rays.