Martin Mittelstaedt, "Ontario's 'dark-sky' park a world first," The Globe and Mail
—Colin Nickerson, “ ‘Sky preserve’ has gazers seeing stars,” The Boston Globe, August 9, 1999
They've done so to improve observing conditions for astronomers, whose view of the sky is increasingly soured by urban lighting. (Example: Southern California has some of the world's most wonderful observatories, but "light pollution" may render the observatories useless as cities, lighted billboards and shopping malls spread from horizon to horizon.)
The New Mexico Legislature recently passed a resolution designating the state a "dark skies" state, reports the newsletter of the International Dark-Sky Association in Tucson, Ariz. The resolution says astronomical observatories and laboratories are an "economical benefit" to the state, and so requests "the cooperation of public and private utilities, billboard owners, counties, municipalities and others owning itself or operating outdoor lights to reduce light pollution."
In June, the Michigan Legislature passed, and Gov. John Engler signed, a law designating an area near Hudson, Mich., as a "Dark Sky Preserve."
Keay Davidson, "Bright lights spawn 'dark skies' preserves," The Salt Lake Tribune, August 5, 1993