Astronomical Images : Reflection of rays within a polemoscope

Johannes Hevelius

Astronomical Images

<p style='text-align: justify;'>The <i>Selenographia</i>, literally meaning 'descriptions of the Moon' was published by Johannes Hevelius (1611-1687) in 1647. In addition to descriptions of the surface of the Moon, the book also contained other telescopic observations by Hevelius, as well as explanations of instruments. The <i>Selenographia</i> is an unusual publication in the extent to which an author controlled the printed presentation of his work. The book contained observations made by Hevelius at his observatory using instruments (several of which he invented or improved upon), drawn and noted down by himself, then engraved by himself ' several images bear the signature: <i>auctor sculpsit</i> (the author engraved) ' and published at his own expense. This avoided complications and errors that might be introduced during the publication process by other artists and printers. The book itself contains a wide range of representations of the Moon, including a series of the surface of the Moon through its phases. Having discussed the component parts of the polemoscope, Hevelius goes on to show the geometrical principles involved in the images projected by the mirrors. He called these figures 'diagrams'.</p>