Astronomy books and documentaries are in the 520s.
Earth Science books and documentaries are in the 550s.
Books on Natural Disasters are in the 360s.
Resources on environmental issues are in the 333s and 363s.
*Earth Science, Natural Disasters, Environmental Issues:
U.S. Environmental Protection Agency
Learning Network of the NY Times
Center for Biological Diversity
Environmental issues web directory
Center for Invasive Species and Ecosystem Health (University of Georgia)
The Swingle Plant Anatomy Reference Collection
Plants Database, by the Natural Resources Conservation Service (U.S. Department of Agriculture)
National Oceanic and Atmospheric Administration
*Space Science:
U.N. Office for Outer Space Affairs
American Association of Variable Star Observers
Exoplanet Exploration, by NASA
Gateway to Astronaut Photography of Earth
NASA (National Aeronautics and Space Administration)
NASA Headquarters LibraryNational Geophysical Data Center
National Space Science Data Center
Space Weather Prediction Center (NOAA/NWS)