Even though the subject is well-defined, reviewing an encyclopedia is always a difficult task, notwithstanding its twelve hundred pages and a hundred forty-eight figures. That being said, a sort of impartial review is facilitated in the present case by the organization of the contents and the style in which the three parts forming this book have been written. Since each part has a principal author, they read in consequence as three individual books, of around 300 pages each. Moreover, a certain objectivity is attained through the numerous citations that form the bulk of each part.
The Laffont encyclopedia of the heavens, under the supervision of Arnaud Zucker, strives to be an introduction to ancient star myths of the Greeks and the Romans, ancient astronomy and astrology. Furthermore, Zucker justifies the book not only for its academic intention, but also for a certain existential purpose: the world of the ancients is the everyday life par excellence, in which we experience the earth as standing still, and man being at the center of the cosmos, notwithstanding the scientific knowledge we have today of the actual workings of the universe. Thus, the ancient astronomical texts have lost none of their beauty and intelligence, since we can still recognize ourselves in them.
The book is divided into three main parts. The first (33-384), written mainly by Arnaud Zucker, is titled "Histoire et mythologie: voir et raconter (History and Mythology: Seeing and Narrating)." The second (385-775), having as principal author Robert Nadal, concerns "Astronomie: observer et calculer (Astronomy: Observing and Calculating)." The third (776-970), authored mainly by Béatrice Bakhouche, concerns heavenly signs and their influence, and the methods of interpretation and prediction. The book ends with a dictionary of astronomical and astrological notions (973-988), a dictionary of astronomers and astronomical authors (989-1062), a catalogue of stars (1063-1158) and a bibliography (1159-1188).
Each part is divided into many thematic sections, which are divided in turn into a presentation, with supporting translations of ancient texts, and commentaries by eleven contemporary scholars (philologists, historians and astrophysicists).
As for the tenor of the text, I will make only one or two remarks. Regarding Plutarch's "lunar purgatory" mentioned briefly on pp. 347-349: Plutarch's heavenly Hades, which is a sort of purificatory place for the disembodied soul, extends from the Earth to the surface of the Moon.  The beautiful study of Bakhouche on the science of astrology in antiquity concludes with the statement that astrology constitutes a large-scale social phenomenon and should not be studied as an obscurantist movement (969-970).
Concerning the translations: aside from the new translations made by the editor and the contributors, most of the French translations are quite old, mainly from the nineteenth century, and thus based on outdated editions (though some of them are revised by the contributors according to newer editions). As for the technical side of astronomy, on pp. 639-775, the reader will find a good exposition not only of the instruments used in astronomical inquiry by the ancients (accompanied by pictures and schemas), but also of the objects, like the Dendera zodiac, the Farnese Atlas, dated to around AD 150-220 (p. 728); a thorough description of the Athenian Tower of the Winds, also called the Horologion of Andronikos Kyrrhestes and build maybe around 160-86 BC (712-727); various parapegmas; and a number of ancient star catalogues.
Worth of mention is the first complete French translation of Hipparchus' commentary on the Phaenomena of Aratus and Eudoxus (549-638), written around AD 140. The encyclopedia contains also an exhaustive comparative catalogue of stars (1063-1158), compiled from Eratosthenes' Catasterismi, Hipparchus' Commentary and Ptolemy's Almagest. To get a sense of the immense work put into this section, we have to remember that Ptolemy mentions 1025 stars, which had to be charted and compared to the ones found in the works of Eratosthenes and Hipparchus, many of which have different names. Each star is thus organized into three parts: boreal, zodiacal and austral constellations (1065).
Though this encyclopedia does not mention or discuses medieval theories of the heavens, it will still be of interest to medieval scholars both as a sourcebook of ancient texts, which are in part the basis of medieval speculations on astronomy, astrology and meteorology, and for its valuable up-to-date bibliography.
1. For a detailed description of the Heavenly Hades, let me simply refer the reader to my book L'Hadès celeste. Histoire du purgatoire dans l'Antiquité (Paris: Garnier, 2015). For Plutarch, see particularly pp. 185-224.