Public Lectures for the Session 2000-2001 held in Room E7 of the Renold Building, UMIST.
Delivered to the Manchester Astronomical Society

18th January 2001

'God's Longitude'

Dr. Duncan Steel, BSc, MSc, PhD, FRAS.
Reader in Space Technology, University of Salford

Standing in for Prof Malcolm Longair, Dr Steel's lecture was one of the most remarkable of the session. His original proposal had been to talk about the calendar but his recent researches, in preparation for a new book, suggested the specific subject of 'God's Longitude'. The first part of his talk was devoted to describing, in detail, lunar motion and the idea of the calendrical month on which can be based a calendar. Historically, the Christian date of Easter was defined from the lunar cycle but the civil calendar was based on the earth's orbit around the sun. The two were slightly incompatible.

It was well known that in 1582 Pope Gregory had decreed that the calendar in the western hemisphere should be adjusted to compensate for the fact that since biblical times the Christian date of Easter, defined from the lunar cycle, had steadily drifted away from the solar Vernal Equinox, 21st March, the first day of Spring in the Northern hemisphere. After 16 centuries Easter could not be reconciled with ancient religious festivities. Even now, the exact time of Vernal equinox can fall within a span of 53 hrs, between 19th and 21st March.

The Gregorian calendar was a Catholic invention and being a Protestant country, England would not adopt it in the 16th century. There was a better alternative, not based on a four-year cycle of 365 days then one of 366 but on a 33yr calendar of 7 periods of 4yrs and one of 5yrs. This was invented by Omar Kyam and is still in use in parts of the Islamic world. It gives much better consistency in which the Vernal equinox falls within a period of 23hrs 16min on 21st March.

In the late 16th century, in Protestant ruled Elizabethan England, plans were afoot at the instigation of a group of secretive collaborators including Dr. John Dee and Sir Walter Raleigh, to introduce this 33yr calendar. But it would mean establishing a new Prime Meridian on the eastern seaboard of America, in territories that were optimistically to be called New Albion. This would be on a meridian 77degrees west of England, "God's Longitude".

Unfortunately, the small expedition of astronomers and surveyors that went out to Virginia to survey and mark the new Meridian were lost in what is now called the Great Dismal Swamp. They were ill-equipped to survive in a hostile and foreign land and their bodies were never recovered, and in 1582 the Catholic Gregorian Calendar was adopted in the Americas. The Gregorian, or Western Calendar, as it can best be described, is a compromise that is useful for trade between the countries of Western Europe and America but is not optimally constructed to tie together the lunar and solar calendars. God's Longitude was never to be.

Synopsis by Kevin J. Kilburn (Secretary)

Maintained by Michael Oates
Page modified 28 October, 2006