Pantheon Sundial

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Published: 02 August 2011

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One of the most iconic buildings in the world, the Pantheon in Rome is an enduring testament to the power and glory of ancient Rome.  At the same time, it has also always posed something of a mystery.  The only source of natural lighting is a thirty-foot diameter hole at the very top of the hemispherical dome, often referred to as the "oculus".

Working since 2009, scholars Guilio Magli and Robert Hannah discovered that at midday on the equinoxes, a shaft of circular light shines through the oculus and illuminates the Pantheon's entrance. 

Read more: Pantheon Sundial

Early Astronomers

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Published: 13 March 2011

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[photo credit: Andrew Caswell and Robert Cockburn of The Daily Telegraph ]

Ask a person what is the earliest evidence of humans building structures to mark significant celestial events, and one offer "Stonehenge".  But there may be a structure built thousands of years early according to some experts in Australia.

A site "down under", name Wurdi Youang, estimated to be older than 10,000 years, has a strange arrangement of stones with alignments toward solstices and equinox that has been scrutinized by several eminent Australian scientists.  They conclude that the placement and alignment of the stones is not an accident and there is a perfect alignment with the setting sun on the mid-summer day. Understandably, the exact location of the site is a well-guarded secret, but it is known to be west of Melbourne approximately 80 kilometers.

Madison Historic Dial Returns

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Published: 13 October 2025

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On October 4, 2025 Madison Historical Society of Ohio was able to have their sundial returned after 32 years, when in 1993 it was moved to the lawn of Lake County Courthouse to reduce the chance of vandalism. The sundial was originally placed at Madison Home 100 years ago on Saturday, October 24, 1925 during a conference of the Women's Relief Society.  From 1904 to 1962 the state ran this building as it was run since 1889, for the needy widows, mothers and children of Ohio’s veterans. They named this building the Madison Home.

Cheryl Swackhammer, president of the Madison Historical Society, opened the rededication ceremony and thanked everyone who had made the sundial's move back to Madison possible. The return of the dial was spearheaded by Kenneth Gauntner, a former Madison Township trustee's and Lake County administrator.

The circular bronze dial with open gnomon sits on a tapered pedestal 3ft (1m) high with a bonze plaque on the pedestal recording the dedication for the Women Relief Society 100 years ago.

Read the article by gmcvey in the Gazette On-Line News at https://gazettenews.com/sundial-monument-rededicated-at-madison-historical-society/

Prosciutto di Portici Sundial's Owner

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Published: 10 June 2025

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The Prosciutto di Portici Sundial, more often called the Portici Ham Sundial, dates from the first century somewhere between  8 BCE to 79 CE.  This small silvered bronze dial was uncovered on 11 June, 1755 in the ruins of Herculaneum (current day Portici) in the "Villa of the Papyri", buried in volcanic ash and charred papyri from the eruption of Mount Vesuvius in 79 CE. The form of the sundial, which resembles a ham, has been extensively studied.  It is an altitude dial with similarities to the cylindrical sundial. 

Live Science reporter Kristina Killgrove writes, "Historians have long assumed that the owner of the Villa of the Papyri was L. Calpurnius Piso Caesoninus, the father-in-law of Julius Caesar."  https://www.livescience.com/archaeology/romans/prosciutto-di-portici-a-portable-sundial-that-looks-like-a-pork-leg-and-it-was-likely-owned-by-julius-caesars-father-in-law-before-mount-vesuvius-erupted

Calpurnius likely commissioned the Epicurean philospher Philodemus to drave the numerous charred scrolls at Villa of the Papyri.  Killgrove commented that "This may explain why the Roman pocketwatch was shaped like a ham. For adherents of Epicurean thought, the lowly pig was often used as a metaphor, as it was seen as a naturally pleasure-seeking creature.

To clarify the use of the dial and the drawn lines attributed in the article as "hours before or after sunset" were actually temporal hours. The lines measuried the hours from sunrise to sunset. Temporary (ancient) hours go across the dial face and vertical lines represent the boundary between the zodiac signs representing the twelve months of the year.  In this dial the twelve months have been “folded” and the month pair labeled between the lines: IUN-IU (June-July), MA-AU (May-August), AP-SE (April-September), MA-OC (March-October), FE-NO (February-November) and JA-DE (January-December).  Notice that both July and August are used and the longest shadows occuring at the end of June while the shortest occur at the end of December.  Further, since July and August are named, the dial was created after the reign of Julius and Augustus Caesar, and in particular when Augustus renamed the month Sextilis to August in 8 BCE.

The Ham dial has a fixed gnomon, the flattened piece at middle-left in the photo.  When properly working, the gnomon is actually much longer and the tip set a specific distance above the dial face and at the upper left corner of the hour-date lines.  To read the time, the dial is rotated from a string at top of the dial until the shadow falls on the vertical date line (or distance between) corresponding to the date. Like the cylindrical sundial, time is read from the downward shadow of the tip crossing the temporary hour line.

The Ham dial also has “folded” hour lines that run across the dial to tell temporary (ancient) hours.  The lines are from top to bottom are for sunrise, 1^st/11^th, 2^nd/10^th, 3^rd/9^th, 4^th/8^th, 5^th/7^th, and at bottom, the 6^th hour line for mid-day.

Historic Sundials of Andalusia

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Published: 16 November 2024

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Esteban Martínez Almirón has published a new book Historical Sundials: Forgotten Andalusian Treasures (Relojes de Sol Históricos Tesoros Andaluces Olvidados) In it he reviews over 400 sundials from the Andalucian region of southern Spain Originally to celebrate the 25th year of the website https://relojandalusi.org/

Esteban Martínez Almirón began showing his sundial drawings on the site. Ultimately more than 60 drawings are in his book, and many are posted on the @stbnart Instagram site. He presents the historical sundials using the themes according to geographical location and building type (e.g. on farms or country houses for daily time telling; churches, cathedrals and other sanctuaries; and civil buildings and public places). Unfortunately many dials have been lost to history and no longer exist.

Martínez Almirón looks briefly at portable sundials of Andalusia, particularly in Sierra de Huelva, the city of Ubeda (where its Renaissance sundials stand out) and the dials of the "New Populations" ("Nuevas Poblaciones"). The book is self-published. If you are interested in purchasing a copy, you can visit https://relojandalusi.org/relojes-de-sol-historicos/. The book cost is 12 euros plus shipping. Text in Spanish.

Rare Astrolabe Discovered by Chance in Verona Museum

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Published: 06 March 2024

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Dr. Federica Gigante, from Cambridge Univerity's History Faculty, discovered a rare astrolabe sequestered in a museum at Verona, Italy.  Publishing in Nuncius (1 March 2024) Dr. Gigante presents "a hitherto unknown remarkable astrolabe from Al-Andalus which likely belonged to the collection of Ludovico Moscardo (1611–1681) assembled in Verona in the seventeenth century. The astrolabe is datable to the eleventh century and features added Hebrew and Latin inscriptions. It underwent many modifications, additions, and adaptations as it changed hands and owners over time thus becoming a palimpsest object. With its added translations from Arabic into Hebrew, the astrolabe closely recalls the recommendations prescribed by the Spanish Jewish polymath Abraham Ibn Ezra (1089–1167) in the earliest surviving treatise on the astrolabe in the Hebrew language written in 1146 precisely in Verona."  Today the astrolabe is preserved at the Fondazione Museo Miniscalchi-Erizzo.

"This isn't just an incredibly rare object. It's a powerful record of scientific exchange between Arabs, Jews, and Christians over hundreds of years," said Dr. Gigante.

Smithsonian Photo Contest - Jaipur Sundial

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Published: 05 November 2023

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Smithsonian Magazine holds a photo-of-the-day contest. Winner on 30 Oct 2023 was Harita Sistu who took a photo of the large sundial of Jantar Mantar, Jaipur India (taken in July 2022). Harita notes: "I wanted to try my best to capture just how massive the instrument is and bring focus into the incredible skill that went into designing and constructing it."

Harita Sistu - Award winning photo of the Equatorial Sundial at Jaipur, India

Indiana French Dial Found

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Published: 27 August 2022

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Smithsonian Collection - Pocket sundial by Bourgaud of Nantes, 1660–1675. (MA.325565)

From the National Museum of American History is an article about "How did a French pocket sundial end up buried in a field in Indiana?" published 20 July 2022 by Kidwell & Schechner.  

It started in 1860 when Dr. Elisha Cannon, while plowing a field in Indiana, came across a strange object. It was a French Butterfield sundial. It ended up in the Smithsonian collection 100 years later, where it quietly sat until recently when curator Peggy Kidwell wanted to learn more. She contacted Dr. Sara Schechner, David P. Wheatland Curator of the Collection of Historical Scientific Instruments at Harvard University, to join the investigation.

The dial is inscribed "Bourgaud Nantes" showing it was from the workshop of a clockmaker in Nantes, France. As with all Butterfield dials it contained a magnetic compass with declination corrections for orienting the dial to north and a miniature plumb bob to hold the dial level. The gnomon support is in the traditional shape of a bird allowing the gnomon itself to be adjusted to a range of latitudes. Look closely at the chapter ring of hour marks in Roman numerals.  Outside the numerals is one hour line scale and on the inside of the numerals is a second scale.  The user could approximate the time between these two scales, done for the extreme latitudes 30 and 55 degrees.

"In her research on sundials in the American colonies, Schechner has drawn attention to several of these dials, and notes that some 18th-century French sundial makers, like Pierre le Maire (and his son of the same name), made pocket dials that carefully listed the latitude of places of French interest in both North and South America." How did the dial end up in Indiana? It could have been carried there by Dr. Cannon and his wife Gulielma, Quakers who in 1840 left North Carolina, finding that "living in a state where African Americans were legally enslaved was intorable." Or the dial may have been left a century earlier when the French occupied much of what is now Indiana, leaving outposts such as Terre Haute and possibly a lost sundial.

Read the article: https://americanhistory.si.edu/blog/pocket-sundial