Light Pollution and Dark Skies: Practice Problem Solutions

1. Artificial light that is wasted or shines where it is not needed. Types include skyglow, glare, light trespass and clutter.

2. About 80 percent.

3. It makes the faintest visible star brighter (a smaller magnitude number), so fewer stars can be seen: perhaps only a few dozen in a big city but thousands in a dark place.

4. Hatchlings head toward the brightest horizon, which should be the sea reflecting the sky. Bright lights from buildings can lead them inland, away from the water.

5. Any three of: shield lights downward; use motion sensors or timers; use warm-color bulbs; turn off unneeded lights; close curtains; use only the brightness needed.

6. Blue-white light scatters more in the atmosphere, brightening the sky and hiding stars more; warm light scatters less.