Updated February 12, 2020 |
Infoplease Staff
- American Astronomical Society: www.aas.org
- Asteroid and Comet Impact Hazards: http://impact.arc.nasa.gov
- Center for Earth and Planetary Studies: www.nasm.si.edu/ceps
- The International Astronomical Union: www.iau.org
- NASA Home Page: www.nasa.gov
- The Nine Planets: www.nineplanets.org
- Planet Quest: http://planetquest.jpl.nasa.gov/
- Space Telescope Science Institute (home of Hubble): www.stsci.edu/resources
- U.S. Naval Observatory: www.usno.navy.mil
.com/ipa/0/1/9/3/5/5/A0193551.html
