John Flamsteed (1646-1719) was a self-taught English astronomer and mathematician who distinguished himself as a young man by his astronomical activities, which included plotting variations in the Sun’s altitude, predicting solar eclipses, and calculating the positions of celestial bodies. He published his findings, corresponded with scientists, and soon came to the attention of the Royal Society. As a result, he was appointed by Charles II to be England’s first Astronomer Royal in 1675. At that time, there was great interest in using astronomical events to calculate the location of a ship at sea. The method for calculating location in latitude had been known since the time of the ancient Greeks, but there was no reliable method for determining longitude. One solution was to use the changing position of the Moon with reference to the background stars as a sort of clock hand, but this required having an accurate catalogue of stellar positions, which didn’t exist. Charles II tasked Flamsteed with creating such a catalogue and supervising the building of a Royal Observatory at Greenwich, which was completed in 1676. His catalogue, the most accurate of its time, was published posthumously in 1725 by his wife and two former observatory assistants, and his great star atlas, Atlas Coelestis, followed in 1729.
When it appeared, the Atlas Coelestis was largest star atlas ever published, and it depicted the individual constellations and their stars in 25 maps. The atlas contained more stars than previous atlases, used a very detailed coordinate system, and based its stellar positions on Flamsteed’s exceptional star catalogue. It was the first major celestial atlas to emphasize the newer equatorial grid system that was centered on the projection of the Earth’s equator into the sky. This more practical system corresponded to the apparent rotation of the heavens as seen from the Earth, and it could be used with greater ease with equatorially mounted telescopes. But as a nod to tradition, Flamsteed’s plates also included a fainter secondary grid system based on the older system centered on the ecliptic (the path of the Sun in the sky). Another feature of Flamsteed’s atlas was the use of the sinusoidal projection (also known as the Sanson-Flamsteed projection), which attempted to improve the distortions in constellation star patterns found in earlier trapezoidal projections by more accurately reproducing the situation that exists on a sphere. These features are shown in the figure, which is the plate from this atlas entitled “Monoceros, Canis Major & Minor, Navis, Lepus” (47.3 X 58.2 cm).
The text and images of this celestial map is from Star Maps: History, Artistry, and Cartography, by Nick Kanas (Springer/Praxis, 2009 [2nd printing]). Dr. Kanas is a Professor of Psychiatry at the University of California, San Francisco, and he does NASA-funded research with astronauts working in space. He has been an amateur astronomer for over 50 years and a collector of antiquarian celestial maps and books for over 25 years. He can be reached at firstname.lastname@example.org. Nick is a “star” CMS member.