Thomas Harriot's Drawings

By Geoff Burt. (Based on an article in Hampshire Sky, November 2008)

First Moon drawing dated 26 July 1609

I’ve had the privilege of researching Harriot’s lunar papers on behalf of Telescope 400. The process has yielded a fascinating insight into the life and work of a Renaissance astronomer. My astronomical speciality is drawing lunar features [1] and this was a golden opportunity to study the work of a pioneer. Harriot’s original astronomical drawings and notes belong today to Lord Egremont but are held by the West Sussex Record Office [2] in Chichester, including lunar phase drawings and a Moon map of c.1611, probably the first of its kind. Microfilm copies [3] are available if you want to go along and see them. The map and a few of the phase drawings are also available on the internet [4].

Born in Oxford in 1560, almost nothing is known of Harriot’s early life but he undoubtedly emerged as a true Renaissance polymath. First and foremost a mathematician, he invented the ‘greater than’ > and ‘less than’ < symbols in algebraic notation. He was also a navigator, explorer and one of the first anthropologists, travelling to the New World in 1585 with Sir Walter Raleigh to study Algonquian Indian society.

By 1605, Harriot was employed under the patronage of Henry Percy, the ninth earl of Northumberland. The earl’s cousin, Thomas Percy, was a leading conspirator in the Gunpowder Plot of that year and during the subsequent investigations Harriot was implicated and imprisoned for a short time. There’s no reason to believe that he was involved with the plot but, not surprisingly, he kept a low profile after his release. Moreover, as a member of the earl of Northumberland’s entourage, Harriot was leading a comfortable life without the need for self-promotion and, in contrast to Galileo, never published his observations.

One of Harriot's Sun Spot drawings

During the early 17th century the English continued to use the Julian calendar, resisting the papist Gregorian system introduced during the latter part of the 16th century. Adjusting by 10 days to convert Harriot’s observation dates to the Gregorian system and using a computer application, in this case ‘Lunar Phase Pro’, produces a very good match against the phase drawings and we can confidently identify what features he was observing. The lunar papers contain over a dozen phase drawings including phases at 3 days, 5 days, first quarter, waxing gibbous and waning gibbous plus the map which may also be regarded as a phase drawing of the full Moon. His very first observation was made when the Moon’s phase was 5 days old; the drawing dated 26th July 1609 [5] by his own hand.

The drawing is little more than a rough ink sketch, as seen through primitive optics at 6X magnification, showing Crisium, Fecunditatis, Nectaris, part of Tranquillitatis, part of Serenetatis and Theophillus/ Cyrillus right on the terminator, but it carries that tremendous significance of being the world’s first telescopic astronomical observation.

Harriot's Moon Map c.1611

Harriot’s Moon map lacks an exact date but post-dates his first phase drawing by some two years. The original map is 6 inches in diameter giving a scale of roughly 1:23,000,000, showing the main maria, high albedo features and craters. The map has a total of 72 letter and number annotations, consisting of letters a to z and numbers 1 to 50 with the exceptions of w and 41. The reason for these apparent omissions is unknown. Note that the Tudor alphabet had 24 letters rather than the modern 26; in those days, I was interchangeable with j and u was interchangeable with v. There’s no key as such because, as a mathematician, Harriot was primarily studying geometrical relationships rather than attempting to name and describe the features he saw. The notes accompanying the map have a series of entries such as, ‘1.23.15, a right line’, ‘1.e.a, equilateral’, and, ‘a.9.13 equilateral almost’, therefore the annotations mark geometric construction points.

However, other notes do include a handful of names and descriptions of lunar features. For example, we know that Harriot called Mare Crisium, ‘The Caspian’. His phase drawing dated 27th August 1610 (Julian calendar) includes the comment “...about 1/3 of ye Caspian was seene.” The phase was waning gibbous or, as he puts it, “3 ½ days after ye Full”. Elsewhere in the notes are references to ‘islands’, ‘promontories’ and significantly, ‘Plato’, ‘Hipparchus’, ‘Tycho’, and ‘Copernicus’ although it’s uncertain whether he applied these names to the same craters as the Jesuit selenographer Riccioli did about 40 years later and with which we’re familiar today. There is a possibility that Riccioli was aware of Harriot’s earlier work.

Finally, there are some quaint asides in the notes when observations were curtailed, "...because I was troubled with ye reume" [6] and elsewhere, “…ye cloudes....shadowed ye Moone.” Some things don’t change!

1 - Hampshire Astronomical Group
2 - West Sussex Record Office, 3 Orchard Street, Chichester, West Sussex. Tel 01243 777100
3 - West Sussex Record Office, Harriot Papers, HMC 241 MP2744.
4 - Galileo Project, Rice University: Catalogue of Harriot's moon drawings (1995)
5 - August 5th 1609, Gregorian.
6 - Rheumatism: Harriot was 50 at the time and, for those days, was getting on a bit!

Higher quality views of the drawings displayed on this page are available by clicking the images.

First published in the Hampshire Astronomical Group Magazine, "Hampshire Sky" November 2008

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