1) The University of Texas at Austin’s McDonald Observatory popularizes science with its “StarDate” updates on public radio and practices the serious stuff from atop Mount Locke and Mount Fowlkes in the Davis Mountains of West Texas, where it’s very, very dark — one of the darkest areas in the continental U.S. www.mcdonaldobservatory.org

2) Some 50 miles southwest of Tucson, in the dim of the Sonoran Desert, the Kitt Peak National Observatory tracks the sun and the stars with the largest collection of optical telescopes in the world, including three major nighttime scopes and 21 others. www.noao.edu/kpno/

3) Twin Keck telescopes — at eight stories tall, the world’s largest optical and infrared scopes — crown 13,796-foot Mauna Kea at the W.M. Keck Observatory on Hawaii’s Big Island. Few surrounding city lights and no mountain ranges to roil the air make the view from here tops with U.S. researchers. www2.keck.hawaii.edu

4) In the Andean foothills near La Serena, Chile, about 370 miles north of Santiago, a cluster of top observatories survey the Southern Hemisphere sky. Eleven European countries maintain the European Southern Observatory (www.eso.org); the National Science Foundation supports the Cerro Tololo Inter-American Observatory (www.ctio.noao.edu); and the Carnegie Institution of Washington runs Las Campanas Observatory (www.ociw.edu/lco). Only the Community Observatory at Cerro Mamalluca (www.mamalluca.org) is open for public night viewing of the Southern Cross constellation and the Clouds of Magellan.