1. Pannekoek’s publications in the reports and proceedings of the Royal Netherlands Academy of Sciences (KNAW) are not downloadable through links to electronic versions in the SAO/NASA Astrophysics Data System (ADS), but these are available through The Digital Web Centre for the History of Science (DWC) of the Royal Netherlands Academy of Arts and Sciences (KNAW) at dwc.knaw.nl?pagina=0&s=Pannekoek&gender=all&type=publication.documents&publicaties.
2. Abbot, C.G., 1914. The direct and scattered radiation of the Sun and stars. Astronomical Journal, 28(16), 129–135.
3. Argelander, F., 1844. Aufforderung an Freunde der Astronomie, zur Anstellung von eben so interessanten und nützlichen, als leicht auszuführenden Beobachtungen über mehrere wichtige Zweige der Himmelskunde. In Schumacher, H.C. (ed.), Schumacher’s Jahrbuch für 1844. Stuttgart & Tübingen, J.G. Cotta, Pp. 122–254 (in German). Translated in 1855 as Handleiding voor vrienden der sterrekunde, tot het volbrengen van belangrijke waarnemingen, die geene werktuigen vorderen, uit het Hoogduitsch vertaald door W.F. Kaiser, met eene voorrede, aanteekeningen en bijvoegsels van F. Kaiser. Zwolle, der erven Tijl (in Dutch).
4. Bahcall, J.N., and Soneira, R.M., 1980. The universe at faint magnitudes. I. Models for the Galaxy and the predicted star counts. Astrophysical Journal, Supplement Series, 44(1), 73–110.
5. Barnard, E.E., 1919. On the dark markings of the sky, with a catalogue of 182 such objects. Astrophysical Journal, 49, 1–24.