Tài liệu tham khảo WikiPedia: 375_Ursula http://adsabs.harvard.edu/full/1984AJ.....89..592M http://ssd.jpl.nasa.gov/horizons.cgi?find_body=1&b... http://ssd.jpl.nasa.gov/sbdb.cgi?sstr=375 http://ssd.jpl.nasa.gov/sbdb.cgi?sstr=375;orb=1 http://occsec.wellington.net.nz/planet/2008/result... //dx.doi.org/10.1086%2F113553
