There was a new moon in the sky on Tuesday. That's the phase, of course, when the moon turns its dark side toward Earth. Once, that meant very dark nights. But increasingly, artificial lighting has brightened the night, casting a diffuse glow far away.

For years this light pollution has interfered with the work of astronomers.

Veteran astronomer Dave Crawford says increasing light pollution means many of the world's most famous observatories can no longer do cutting-edge astronomy.

"Mt. Wilson, where the expanding universe was discovered and worked on by [Edwin] Hubble, can't do that kind of stuff anymore," he said. "Palomar is severely impacted. And so one goes to North-central Chile or the Big Island in Hawaii or the Namibian desert or other places. And yet even there, of course, these being nice, clear, wonderful places, [they] tend to get impacted by people moving in and bringing their lights along with them. So it's a real problem."

Crawford now heads the International Dark-Sky Association, which is working to raise awareness of the issue.

He says much light pollution comes from poorly-designed lighting fixtures, such as streetlights that don't direct their light downward. Dark sky advocates say it's wasteful and creates pollution from unneeded power generation. Light scatters, hitting dust particles and water molecules in the atmosphere, diffusing into a glow that covers the skies around big cities and increasingly in less-populated areas as well.

Crawford says the absence of dark nights may also disrupt biological cycles.

"Whether it's sea turtles, or birds, or trees, or plants. There's no question that recent studies indicate that the lack of a good circadian rhythm - you know, the day/night cycle - is impacting human health. We need that day/night cycle. Everything has had it over the entire history of the earth. And to take it away in only a few decades is a dangerous thing to do," Crawford said.

Several years ago, Jennifer Barlow, who was then in high school, launched a campaign to get people to turn off their lights - at first for just one night - so they could see the night sky better. The campaign led to National Dark Sky Week, which began Tuesday with the new moon. It's not an official event, though many in the astronomy community have embraced the idea. Barlow, who is now a student at the University of Virginia, says Dark Sky Week is more about raising awareness of light pollution than actually getting people to turn off their lights.

"Really turning off the lights for one week isn't going to do very much," she admitted. "But [by] becoming more aware and learning about the proper lighting fixtures, we'll be able to make the skies have a better quality and be darker for years and years to come."

The quality of the night sky is important to Dennis Erickson, a Chicago high school teacher and advocate of sidewalk astronomy, where amateur astronomers take their telescopes out on the streets to share some of the wonders of the night sky with city dwellers. But in a big city like Chicago, he says light pollution obscures all but the brightest objects in the sky, and that robs people of the sense of wonder that a really dark sky brings.

"To get that serious, awe-inspiring feeling of looking at the night sky - especially seeing that Milky Way - when that shows up, it sort of gives you a chill down your back, and you wonder what in the world is out there. Is there life out there? And now, if you live in the city and don't get out in the country, you don't experience that, and, you know, most of our inner city kids do not get out, and they never see that beautiful Milky Way," Erickson said.

However, Jennifer Barlow has some suggestions for what you can do in the meantime.

"Turn off the lights," she recommends. "That's one of the most important things, because if people don't participate, then it's not going to work. Actually tell other people, because not everybody's going to hear about it."

The originator of National Dark Sky Week suggests people "go out and look at the sky and just see what the dark sky has to offer us. Hopefully that will encourage people to get better lighting and be more aware about light pollution."