February 1996 page 36
René R.-J. Rohr

The Astrolabe

A historical overview of the astrolabe, its design, use in navigation and astronomy, and its gnomonic significance.
Dials: Astrolabe

June 1995 page 32
René R.-J. Rohr

On Lunar Nomograms

A mathematical examination of lunar nomograms and their use in timekeeping, possibly as an analytical or design tool involving the moon's cycles.
Dialling Tools, Mathematics of Dialling

June 1994 page 42
René R.-J. Rohr

Portable Sundials in Ancient Rome

A historical overview of portable timekeeping devices in Roman times, such as ring dials and folding dials. The article discusses their construction, inscriptions, and cultural significance, providing archaeological context and interpretations of surviving examples.
Dials: Portable, Historical Dials

October 1994 page 36
René R.-J. Rohr

Lunar Distances

This article discusses the historical method of determining longitude at sea using lunar distances, especially before accurate marine chronometers became widely available. It explains the principle of simultaneous observation of lunar positions relative to stars or planets, and the complex calculations required to correct for various astronomical factors. The article traces the development of lunar ephemerides (tables) from early proposals to the precise tables published by Tobias Mayer in the 18th century and their adoption in national nautical almanacs. It also describes the instruments used, like the sextant, and the intricate process sailors followed, noting the eventual decline of the method with the advent of accurate chronometers and radio communication.
Historical Dials

February 1993 page 3
René R.-J. Rohr

Some Reflections on Neolithic Astronomy

This study reflects on prehistoric astronomic notations found on scratched pebbles from a cavern, dating back 8-10,000 years. It discusses observations of the sun and moon to mark seasons and years, including lunar cycles like the 18.62-year cycle of extreme moon sets and the 19-year Meton cycle, possibly recorded in megalithic monuments like Stonehenge.

October 1993 page 2
René R.-J. Rohr

The Sundial of the Old Franciscan Church in Rouffach

This article details the restoration of a unique astronomical chronogram sundial in Rouffach, France, dating from the early 17th century. It describes the fresco's depiction of planetary orbits based on Ptolemy and Tycho Brahe, highlighting challenges in deciphering faded inscriptions and the astrological significance of a lunar eclipse on the original dial's date in 1617.
Dials: Unusual, Dials: Vertical, Historical Dials, Restoration projects, Sundial Design & Layout

February 1992 page 5
René R.-J. Rohr

Astronomical Endeavours and Highlights under Allah's Sun

This article explores Islamic astronomy's role in determining prayer times, particularly the challenge of twilight in higher latitudes like Brussels where true night is absent around summer solstice. It discusses the use of astrolabes and the historical importance of observatories like Maragha and Samarkand, highlighting their monumental instruments and the Koran's influence on precise astronomical observations. It also mentions Maharaja Jai Sing II's five observatories in India, especially the Jaipur Great Samrat Yantra.
Dials: Astrolabe, Mathematics of Dialling

July 1991 page 25
René R.-J. Rohr
E. J. Tyler
Gordon E. Taylor

Book Reviews

This section features reviews of three books. 'Bizkaiko Eguzski-Erlojuak' is a bilingual catalogue of Biscayan sundials. 'Georg Hartmann of Eggolsheim' studies a Franconian mathematician and instrument-maker. 'Sundials' by Mayall and Mayall, reviewed by Gordon E. Taylor, notes updates but also highlights production errors and a persistent 'howler' regarding moon dial observation, emphasizing revision importance.
Book Reviews

October 1991 page 16
René R.-J. Rohr

The Da'ire-Yi Mu'Addil

Rene R.-J. Rohr introduces the 18th-century Islamic instrument known as the "da'ire-yi mu'addil" (equatorial circle), used for determining daily and nightly prayer times. Driven by religious prescriptions, Islamic scientists developed sophisticated astronomical and mathematical methods. This instrument, although not mathematically precise, allows for the determination of prayer times, especially night prayers like isha and subh, through observation of the sun and moon's positions.
Dials: Equatorial, Historical Dials, Dials: Nocturnals

February 1990 page 8
René R.-J. Rohr

The Sundials of the Kappelturm Gallery at Obemai.

This article describes the sundials located on the Kappelturm (bell tower) of the former Notre-Dame church in Obernai, where 16th-century watchmen improvised sundials scratched directly onto the walls when their mechanical clock malfunctioned. It identifies two sundials on the East face, nine on the South face, and one on the West face. The author notes their inaccurate construction due to the watchmen's lack of gnomonic principles, describing them as "caricatures" of true dials. The article includes detailed figures and footnotes explaining the dial configurations and their historical context, including the use of Roman and Arabic numerals.
Dials: Mass Dials

June 1990 page 14
René R.-J. Rohr

A Unique Greek Sundial

This article describes the 1975 discovery of a unique Greek sundial slab at Ai Khanoum, Afghanistan. Dating between 325 and 145 B.C., this polar dial, designed to indicate temporary hours, represents an evolutionary advancement in ancient gnomonics, despite a discrepancy between its marked latitude and discovery site.
Dials: Polar, Historical Dials, Dials: Scaphe

October 1990 page 5
René R.-J. Rohr

On Reflected Ceiling Dials

This article explores the history and theory of reflected ceiling sundials, referencing figures like Isaac Newton and Christopher Wren. It discusses examples such as the Palazzo Spada in Rome, the Lycee Stendhal in Grenoble, and a unique staircase dial in Saint-Antoine-en-Vienne, along with their design principles and historical context.
Dials: Reflected, Historical Dials, Sundial Design & Layout

July 1989 page 5
René R.-J. Rohr

Lambert's Circles

An article by Rene R-J. Rohr discusses Lambert's circles and their relationship to analemmatic sundials. The article discusses how to determine the times of sunrise and sunset using these circles, including their application to the universal dial of Antoine Parent, and how they can be used to create a sun compass.
Dials: Analemmatic, Mathematics of Dialling