Não informado. Publications of the Allegheny Observatory of the University of Pittsburgh. University of Pittsburgh.
Chicago-referens (17:e uppl.)Não informado. Publications of the Allegheny Observatory of the University of Pittsburgh. Lancaster, Pa: University of Pittsburgh.
MLA-referens (8:e uppl.)Não informado. Publications of the Allegheny Observatory of the University of Pittsburgh. University of Pittsburgh.
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