The first comprehensive star atlas built on telescopic observation, mapping the heavens as seen from Greenwich
What the Work Is
The Atlas coelestis is a star atlas published posthumously in 1729, compiled from observations made by John Flamsteed, the first Astronomer Royal, at the Royal Observatory in Greenwich. Though Flamsteed died in 1719, the work was brought to press a decade later by his widow, Margaret Flamsteed, with assistance from Joseph Crosthwait and Abraham Sharp. The atlas is widely regarded as one of the most significant celestial atlases of the eighteenth century and holds the distinction of being the first comprehensive star atlas based entirely on telescopic observations.
What the Book Is About
The atlas presents a systematic visual record of the night sky as visible from Greenwich, containing more than 3,300 stars plotted for the epoch 1690. Its purpose was to correct the accumulated errors of earlier celestial cartography, particularly those found in Johann Bayer’s Uranometria of 1603. Flamsteed’s approach differed from his predecessors in a fundamental way: rather than depicting constellations as they might appear mirrored or reversed, he showed them from the front, consistent with the descriptions handed down from Ptolemy. The work thus represents both a corrective to past inaccuracies and a new standard for representing the heavens.
Key Ideas and Themes
The Atlas coelestis introduced several innovations that would shape the future of celestial mapping. Most notably, it was the first atlas to combine multiple constellations on a single double-page plate, a departure from the practice of Bayer and Hevelius, who had devoted separate plates to individual constellations. This consolidation across 25 double-sided plates anticipated the layout of modern star atlases.
The atlas also pioneered a systematic classification of stellar brightness. It was the first work to divide stars into seven distinct magnitude classes, a scheme that provided astronomers with a consistent framework for describing and comparing stellar visibility. This ordering of stars by brightness was a significant step toward the standardized magnitude system still used in astronomy today.
For the southern hemisphere, Flamsteed drew on observations made by Edmond Halley during his 1677–1678 expedition to the island of St. Helena. Halley’s southern data allowed the atlas to extend its coverage beyond the northern skies visible from Greenwich, and Flamsteed adopted Halley’s introduced constellation Robur Carolinum, a now-obsolete grouping that has since fallen out of official recognition.
The atlas was notable not only for its content but also for its physical scale. Its plates measured approximately 61 by 51 centimeters, making it the largest-format celestial atlas of its time as well as the most comprehensive. The constellation figures were illustrated by James Thornhill in the Rococo style, lending the scientific work an artistic dimension, while the two planispheres were designed by Abraham Sharp.
Structure and Approach
The work comprises 25 maps of the constellations visible from Greenwich, supplemented by two planispheres. Flamsteed’s method was grounded in his own observational practice at Greenwich, where he had assembled one of the most precise instrument collections of the era. Lacking generous state funding, he had largely constructed or financed his own observational equipment. From 1689 he used a seven-foot mural quadrant made by Abraham Sharp, which incorporated several technical innovations: Gascoigne’s telescopic sights with crosshairs, Picard’s reticle eyepiece, and Ole Rømer’s improved micrometer. With an observational accuracy of roughly twelve arcseconds, this instrument ranked among the most precise of its time. For timing meridian transits, Flamsteed relied on precision pendulum clocks by Thomas Tompion, which crucially enhanced the accuracy of his measurements.
The atlas was accompanied by a related catalog, the Historia coelestis Britannica, published in 1725. This catalog contained the positions of more than 3,000 stars—approximately twice the number recorded in Tycho Brahe’s sixteenth-century catalog—and covered 55 constellations, including 46 following Ptolemy and nine attributed to Hevelius, among them Canes Venatici, Lacerta, Leo Minor, Lynx, Sextans, and Vulpecula, as well as Monoceros and Coma Berenices.
Significance and Influence
The Atlas coelestis set a new benchmark for celestial cartography, both in the accuracy of its star positions and in the comprehensiveness of its coverage. Its publication history reflects its lasting utility: throughout the eighteenth century, several reduced-size editions appeared, as the large-format plates were considered unwieldy for practical use. In 1776, a revised French edition was published in Paris by Nicolas Fortin under the title Atlas Céleste, edited by Le Monnier, Pasumot, and La Caille, with star positions updated to the year 1780. A further edition in 1795 by Méchain and Lalande incorporated Messier objects for the first time, including Méchain’s new discoveries M104 and M105 through M109. In 1782, the German astronomer Johann Elert Bode published a corrected and expanded version of the 1776 Fortin edition under the title Vorstellung der Gestirne. These successive editions demonstrate the atlas’s enduring role as a foundational reference for astronomers throughout the century following its initial publication.
The publication of the atlas was delayed significantly by financial difficulties. Margaret Flamsteed encountered monetary problems following the collapse of the South Sea Bubble in 1720, which set back the work’s production. The atlas was ultimately issued in 1729, edited by Margaret Flamsteed with the assistance of Joseph Crosthwait and Abraham Sharp. A digitized version of the 1729 London edition notes that it was published by Margaret Flamsteed and James Hodgson.
