One of Riccioli's most significant works was his 1651 Almagestum Novum (New Almagest),The old Almagest was Ptolemy's second-century book. an encyclopedic work consisting of over 1500 folio pages (38 cm x 25 cm) densely packed with text, tables, and illustrations. It became a standard technical reference book for astronomers all over Europe: John Flamsteed (1646–1719), the first English astronomer royal, a Copernican and a Protestant, used it for his Gresham lectures; Jérôme Lalande (1732–1807) of the Paris Observatory cited it extensivelyBut not necessarily favorably—some discussion of Lalande citing Riccioli is available in Galloway 1842 (pp. 93–97). even though it was an old book at that point; the 1912 Catholic Encyclopedia calls it the most important literary work of the Jesuits during the seventeenth century.Van Helden 1984 (p. 103); Raphael 2011 (pp. 73–76), which includes the quote about "no serious seventeenth century astronomer" on p. 76; Campbell 1921 (p. 848); Catholic Encyclopedia: Giovanni Battista Riccioli. Within its two volumes were ten "books" covering every subject within astronomy and related to astronomy at the time:
