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Fascinating study of the sun and its planets, and also the various moons of the planets.
This remarkable 1774 astronomical diagram by Samuel Dunn offers an interesting representation of the relative sizes of celestial bodies and the distances between satellites and their parent planets, based on the most current astronomical knowledge of the time.
Dominating the upper half of the chart is an immense semi-disc labeled THE SUN, occupying more than half the page to emphasize its overwhelming scale relative to the rest of the solar system. The sun is rendered with a visible radius extending nearly 432,000 miles, and a "Diagonal Scale of Miles" spans the top margin. Radiating outward from the sun’s edge along curved lines are the names and relative positions of the primary planets—Mercury, Venus, Earth (with its Moon), Mars, Jupiter, and Saturn. Uranus (discovered in 1781) and Neptune (1846) are absent, as this map predates their identification.
Beneath the solar hemisphere, Dunn includes two detailed insets with scaled drawings of Jupiter and Saturn, complete with their known satellites and rings. The text surrounding these insets elaborates on each planet’s diameter, volume, and the orbital distances of their moons. For Jupiter, the magnitudes and distances of its four principal moons—discovered by Galileo—are given with exactitude. Saturn’s ring system is shown in cross-section, and its five known satellites (as of the early 18th century) are detailed, including measurements of their orbits and observations of their behavior.
Each of these annotations is rooted in observational astronomy, referencing the work of astronomers such as Cassini, Flamsteed, and Halley, with Dunn also citing his own observations. The Moon's distance from the Earth, as well as the relative scales of all planetary bodies included, are rendered in such a way as to emphasize both comparative magnitude and proportional distance.
Samuel Dunn (bap. 1723-1794) was a teacher of mathematics and navigation who published, among other things, maps and charts. Although information about his early education is lacking, by age nineteen he was leading his own school and teaching writing, accounting, navigation, and mathematics in Devon. In 1751, he moved to London, where he taught in several schools and tutored privately.
By the 1760s, Dunn was known as a respected astronomer and had published a range of textbooks on math, navigation, and astronomy. After the publication of the Nautical Almanac, Dunn acted as a certifier of ships’ masters under the new system, on behalf of the Board of Longitude. He performed similar work for the East India Company, as well as made charts of the East Indies. In 1776 he published A New Variation Atlas and, in 1777, A New Epitome of Practical Navigation, or, Guide to the Indian Seas. By 1780, he was named editor of the New Directory for the East Indies, which included his own charts. In 1786, he released a pioneering study, Theory and Practice of Longitude at Sea. He also designed several instruments for navigation.
Dunn died at his home in Fleet Street in January 1794. His books and maps were auctioned at Sothebys in a sale of over 1,000 lots. Many of these were bought by Alexander Dalrymple, hydrographer of the East India Company and soon-to-be-named first head of the Hydrography Office.
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