I believe if you look up (using Google or Wiki) the term refraction or heat refraction you might gain a better understanding of what you're visualizing. The heat (not the light) emitted causes the atmosphere or ambient surroundings to appear to 'wiggle' thus causing a fuzzy or distorted appearance.
For more info, see the following excerpt:
BTW, if it were truly total
blackness, you'd see nothing! You're probably seeing a limited amount of light. If it appears to be coming from behind you, then it's probably being reflected back at you from somewhere. Your eyes (look up rods and cones ...parts of the cornea) take 5 minutes or more to get used to the dim available light and can 'see' better with using that limited amount of light. When it's cold, you are not being light polluted. If you look away from those heat sources like cities, homes, cars, exhausts and other sundry heat sources.