Simon Cassidy

Simon Cassidy studied mathematics in his native England and later worked as a software engineer on medical devices in California. He had an IQ of 180. His scholarly interests included calendar studies and the prehistory and history of mathematics and astronomy. He was an authority on the astronomy of Stonehenge, and studied the role of John Dee in the history of mathematics, calendars, and geography (see below). One of his projects was to gain recognition for a correct understanding of the vernal equinox year, its role in the history of the calendar and its correct measurement.

Simon Cassidy's last email communication to this writer was in mid-2018. After that it seems his health worsened progressively. He died at a nursing home in Petaluma, CA, in early-January 2023.


Documents on this site by Simon Cassidy
(these are mostly messages sent to the CALNDR-L mailing list):

  1. Error in Statement of Tropical Year
  2. The Tropical and the Anomalistic Year
  3. Comment on Future Accuracy
  4. Re 4-1/8 yr. Leap Rule responses of Richard, Jim and Amos
  5. Implementing a correct 33-year calendar reform
  6. Re: How long is a year -- EXACTLY?
  7. Lengths of "seasons"
  8. Re: Calendar question for Simon Cassidy
  9. Multiplex Perpetual Solar Calendarium
  10. Re: Lunar systems (Jewish)
  11. Re: Query (Peter's reply)
  12. Re: Query (Buckley's reply)
  13. Re: Intel and Stonehenge
  14. Re: Stonehenge speculation (lunations and lintels)
  15. Stonehenge et al (75-stone model)
  16. The week of weeks, of nights of full-moon.
  17. The Week of Weeks of Nights of Full Moon
  18. Re: The Week of Weeks of Nights of Full Moon
  19. The Ideal Metonic Epacts for the Next 4K Vernal-Equinox Calendar-Years
  20. Response to Leap Week Calendar Proposal by W.Z.
  21. Response to Lars Osterdahl re ISO Leap Weeks

Stonehenge central structure, ca. 20th century AD
(ruin of sarsen structure and bluestone additions).
Central sarsen reconstruction, ca. 20th century BC
(before bluestones were returned to the monument).
Simon Cassidy's photographic reconstruction of Stonehenge
(Reconstruction image © 1994 Simon Cassidy; reproduced here with permission.)

Two of Simon Cassidy's works that are reproducible on this website are:
Simon wrote a couple more articles on calendar-related matters for his website, which he began in 2013 (or earlier) and which is no longer online. A copy as at January 11, 2019, is available on the Wayback Machine here.