Light sent upward is reflected back to the ground by dust, water vapor and air molecules, according to a NASA report published in 2001. It cited a study that said perhaps two-thirds of the world's population cannot see the Milky Way at night.
Los Angeles is one of the cities from which it is not visible. Light pollution has erased much of the night sky for decades, said Ed Krupp, director of the Griffith Observatory. In 1986, many Angelenos couldn't see Halley's Comet with the naked eye, Krupp said.
Efforts by the Los Angeles Bureau of Street Lighting to combat light pollution by capping the tops of street lights to deflect light down have made a difference, Krupp said. But commercial lights, including the strobing search lights used to attract attention, have worsened the situation.
"A perpetual operation, night after night, causes severe problems for looking at an object in that part of the sky," Krupp said.