Thomas Jefferson's 1811 Eclipse Observations

LWS 1197, Thomas Jefferson to John Payne Todd, October 10, 1811
(referring to September 17, 1811 solar eclipse)

Today North Americans celebrate The Great American Eclispe! At around 1:22 pm EST, Morristown will begin to experience coverage, achieving maximum coverage at around 2:44 pm EST. These astronomical events have intrigued humans for thousands of years. ☀ In fact, in January 1777, shortly after arriving in Morristown, General George Washington penned a letter to Thomas Wharton with concerns about quelling any superstitious reactions by his troops. This event took place during the first Morristown encampment, while the General was lodging at Arnold's Tavern. ☀ Washington was not the only 'founding observer' of eclipses. Thomas Jefferson was known to have attempted to observe at least four solar eclipses in his lifetime. Morristown NHP houses Jefferson's September 17, 1811 observations in a letter to John Payne Todd (son of Dolley Payne Todd Madison). His notes focus on the phases of contact and the exact times he witnessed its path.

To John Payne Todd

Monticello Oct. 10. 11.

Dear Sir

According to promise I send you our observations of the solar eclipse of Sep. 17. we had, you know, a perfect observation of the passage of the sun over the meridian, and the eclipse began so soon after as to leave little room for error from the time piece. her rate of going however was ascertained by 10. days subsequent observation and comparison with the sun, and the times, as I now give them to you are corrected by these. I have no confidence in the times of the 1st & ultimate contacts, because you know we were not early enough on the watch, decieved by our time piece which was too slow. the impression on the sun was too sensible when we first observed it, to be considered as the moment of commencement, and the largeness of our conjectural correction (18″) shews that that part of the observation should be considered as nothing. the last contact was well enough observed, but it is on the forming and breaking of the annulus that I rely with entire confidence. I am certain there was not an error of an instant of time in either. I would be governed therefore solely by them, and not suffer their result to be affected by the others. I have not yet entered on the calculation of our longitude from them. they will enable you to do it as a college exercise. affectionately yours

Th: Jefferson

	H	′	″
1st contact	0–	13–	54
annulus formed	1–	53–	0		central time	H   ′   ″		central time	H   ′   ″
annulus broken	1–	59–	25		of annulus.	1–56–12½		of the two contacts	1–51–28
ultimate contact	3–	29–	2

Latitude of Monticello 38°–8′

☀ Transcription via founders.archives.gov

Learn more about these historical astronomical activities:

☀ January 8, 1777

☀ September 17, 1811