Abell, George O. (1958). "The distribution of rich clusters of galaxies. A catalogue of 2,712 rich clusters found on the National Geographic Society Palomar Observatory Sky Survey". The Astrophysical Journal Supplement Series. ج. 3: 211–88. Bibcode:1958ApJS....3..211A. DOI:10.1086/190036.
Abell, George O. (1958). "The distribution of rich clusters of galaxies. A catalogue of 2,712 rich clusters found on the National Geographic Society Palomar Observatory Sky Survey". The Astrophysical Journal Supplement Series. ج. 3: 211–88. Bibcode:1958ApJS....3..211A. DOI:10.1086/190036.