Analysis of information sources in references of the Wikipedia article "Nebula Cincin" in Indonesian language version.
|bibcode=
(bantuan). doi:10.1888/0333750888/5323. ISBN 0-333-75088-8. Article ID #5323.|bibcode=
(bantuan). doi:10.1888/0333750888/5323. ISBN 0-333-75088-8. Article ID #5323.