I use a Leeds and Northrup Optical Pyrometer to measure temperature. It's basically a lens with a lightbulb filament across the center. You turn a dial on the side and it gives more power to the filament and makes it glow brighter. If I look at something thats 800C and set the filament at 600C the filament looks black. When I reach 800 on the dial it disappears because it's the same temperature as what I'm looking at. If I crank it up to 810 and keep going the filament gets brighter and brighter. Your shaft of sunlight looks bright because there is more energy in it than the surrounding air. If you could bottle the light from another section of the sky that doesn't have the beam and open it back up in the middle of the night You'd see a great whopping beam there. It makes a lot more sense now that I'm into my first Corona.