A brief introduction to coronal 'loops'

A discussion is presented of elementary aspects of the physics of coronal loops, in order to more securely approach the question of their existence. It is noted that the time-scales for pressure equilibration are far shorter than typical cooling times in loop structures, and that the loop structures are accordingly in pressure balance with their surroundings. Those surroundings, however, are dark, implying a decreased density and gas pressure outside the bright loops. It is deduced that the loop interiors must have a weaker magnetic field than the gas immediately outside them.