The box lid, depicting the muse of astronomy, Urania
Urania's Mirror illustrates 79 constellations, some of which are now obsolete, and various subconstellations, such as Caput Medusæ (the head of Medusa, carried by Perseus). It was originally advertised as including "all the constellations visible in the British Empire", but, in fact, leaves out the southern constellations and, by the second edition (1825), advertisements merely claimed illustration of the constellations visible from "Great Britain". Some cards focus on a single constellation, others include several, with Card 32, centered on Hydra, illustrating twelve constellations (several of which are no longer recognised). Card 28 has six, and no other card has more than four. Each card measures 8 inches by 5 1⁄2 (about 20 by 14 cm). A book by
Jehoshaphat Aspin entitled A Familiar Treatise on Astronomy (or, to give its full name, A Familiar Treatise on Astronomy, Explaining the General Phenomena of the Celestial Bodies; with Numerous Graphical Illustrations) was written to accompany the cards. Both the book and cards were originally published by Samuel Leigh, 18 Strand, London, although the publishing firm had moved to 421 Strand and changed its name to M. A. Leigh by the fourth edition. The cards and books came within a box illustrated with a woman almost certainly intended to be Urania, muse of astronomy.
P.D. Hingley calls it "One of the most charming and visually attractive of the many aids to astronomical self-instruction produced in the early nineteenth century". On its main gimmick, the holes in the stars meant to show the constellation when held in front of a light, he notes that, as the size of the holes marked correspond to the magnitude of the stars, a quite realistic depiction of the constellation is provided. Ian Ridpath mostly concurs. He describes the device as an "attractive feature", but notes that, due to the light at the time being provided primarily by candles, many cards likely burned up due to carelessness when trying to hold them in front of the flame. He notes three other attempts to use the same gimmick—Franz Niklaus König's Atlas céleste (1826), Friedrich Braun's Himmels-Atlas in transparenten Karten (1850), and Otto Möllinger's Himmelsatlas (1851), but states that they lack Urania's Mirror's artistry.