G. O. Abell: Globular Clusters and Planetary Nebulae Discovered on the National Geographic Society-Palomar Observatory Sky Survey. In: Publications of the Astronomical Society of the Pacific. Band67, August 1955, ISSN0004-6280, S.258, doi:10.1086/126815 (iop.org [abgerufen am 27. Dezember 2021]).
iop.org
iopscience.iop.org
G. O. Abell: Globular Clusters and Planetary Nebulae Discovered on the National Geographic Society-Palomar Observatory Sky Survey. In: Publications of the Astronomical Society of the Pacific. Band67, August 1955, ISSN0004-6280, S.258, doi:10.1086/126815 (iop.org [abgerufen am 27. Dezember 2021]).
G. O. Abell: Globular Clusters and Planetary Nebulae Discovered on the National Geographic Society-Palomar Observatory Sky Survey. In: Publications of the Astronomical Society of the Pacific. Band67, August 1955, ISSN0004-6280, S.258, doi:10.1086/126815 (iop.org [abgerufen am 27. Dezember 2021]).