NEW YORK -- The Survivor Tree at the World Trade Center will be lit in blue Wednesday night in memory of the victims of the war in Israel. The tree was also illuminated Tuesday night. The tree ...

Complicated physics makes these molecules scatter more blue ... at sky brightness—what they call the sky background—they use a unit of brightness per area of the sky: how much light is spread ...

But LEDs also emit more short-wavelength blue light, which scatters off particles in the atmosphere more than sodium bulbs’ orange light, creating more sky glow. Existing satellites are not ...