​Original version

A PENA BICUDA: DESCRIPTION AND CHARACTERISTICS OF THE MEGALITH

In Doniños, shortly before reaching Canelas beach (Cabo Prioriño), a rock located near the road used to draw attention. It was in 1987 when I first approached to study it, due to its menhir-like shape, very similar to those documented throughout Europe. This rock did not go unnoticed; local residents know it as A Pena Bicuda (Pointed Rock) or Pena Bienda.

Geographical location and discovery of the archaeological site

This singular rock was located on the hill (Canelas area) 70 meters from the road, and 500 m from the seashore at an elevation of 50 m above sea level. From this spot, one can see a vast panoramic view of the entrance to the Ferrol Estuary and the Tower of Hercules (A Coruña), which is located directly opposite. The megalith is (was) a local granite stone measuring 2.5 m in height, 2.4 m in length from N to S, and 70 cm in width (E-W) on the north face, which then tapers to a point (triangular plan) on the south face. It presents an irregular prismatic pyramidal shape and was worked (chiseled) on its three faces, with an approximate weight of three tons. Viewed from the north face it is flat (vertical) and from the south face it presents a vertical and inclined edge, the termination of the two triangular faces, one to the E and the other to the W.

The standing stone (menhir) was accompanied on the east face by several smaller natural stones of the terrain and on the west face by a small prehistoric "arca" (burial chamber) of medium dimensions.

THE ALIGNMENT OF THE SUNDIAL MARKERS (STONES) AND THE ASTRONOMICAL FINDING

But the main characteristic of this site is that on the north face, completely covered by gorse, at a distance of 2.60 m from the standing stone, there was an alignment in an E-W direction (almost exact) of seven smaller stones (approx. 1/2 m) at a certain distance from each other, and two smaller stones (40 cm) near the base of the standing stone, all of them firmly fixed in the ground, which initially were not visible as they were totally covered by gorse and fern vegetation. The entire complex was located on a slightly sloping hill plain (N-S), forming two axes of symmetry, one of 8 m E-W and 6 m N-S (See figures 1, 2 and 3).

In spring, on a sunny day, it was observed how the tip of the shadow of the standing stone (menhir) was touching "exactly" one of the stones in the alignment; it seemed to be marking something (stone no. 3) and it could be a sundial. Thus, by measuring the time the tip of the shadow took to pass from one stone to the next, surprisingly, this time was exactly one hour across all stones, confirming it was a sundial (horizontal type). Later on, a fire on the hill left the entire archaeological monument exposed from the vegetation that covered it, allowing the entire structure that configured it to be perfectly seen (local granite stones). On different days (with sun), relevant dates of the annual calendar were also well marked by the tip of the shadow on the rocks.

OPERATION OF THE SUNDIAL

This Canelas sundial was of a flat horizontal type with a surface parallel to the horizon.  The alignment of the 'stones' marks each hour (nine hours), which is the time it takes for the shadow to pass from one to another: four hours before midday, the hour of midday, and four hours after. This row of stones was to the north of the standing stone (menhir), which at an average distance of 2.60 m acts as a gnomon/style and projects the shadow, touching the markers (stones) from October to February (five months); after that, it continues marking the hours by approximation (prolongation of the shadow) but the shadow does not touch the 'stones' (markers) until reaching October again, which indicates that the construction to place them was carried out between those months, most likely in February or November. To facilitate the vision of the graph, the 'stones' (hour markers) are numbered from 1 to 9.

Operation of the Sundial: In the month of November, the length of the shadow touches all the stones in its transit (nos. 1, 2, 3, 4 to 9). 'stone' no. 7, of greater length, was canteed so that the shadow marked three hours: 14h, 15h (in the middle) and 16h. Shortly after sunrise, the shadow of the standing stone touches the first 'stone', no. 1, at 8:34h;  no. 2 at 9:34h; no. 3 at 10:34h, etc., until no. 9 at 16:34h (4:34 PM) in the afternoon, (wrist-watch hours), and the shadow projection continues but now without markers until it disappears at sunset. Thus marking four hours before midday, the midday hour ('stone' no. 5) and four hours after (9 hours). Note: stone no. 4 is missing due to agricultural work and the use of stones from the hills for various purposes, but where it was located is perfectly perceived by the indentation in the ground and the perfect "symmetry" of the measurements. Also, 'stone' no. 6 was cut at ground level but maintained its position and remained visible. There could have been more 'stones', as old aerial photographs seem to show, since the markers for hours before and after those indicated here do not currently exist.

From the study of this set of 'stones' that define the clock, it is clear at a glance that the "midday/12h" hour is very well marked by a 'stone' carefully worked and situated on the N–S central axis relative to the standing stone. It should also be noted that the meridian line at this location was not "exactly" well calculated, as the sun passes through it approx. about 12 minutes early; both this and other errors are very common in sundials, especially medieval ones, as their calculation and construction require astronomical knowledge and a very careful and fine technique in their layout, although several practical graphic methods have existed since ancient times to solve this problem. It is also worth noting that the sun's passage through the meridian is different every month as it obeys the variation due to the equation of time. In view of all that has been indicated, the builder(s) was a person with certain knowledge and experienced in this type of work. It is also possible that a portable sundial was used as a guide.

Cabo Prioriño Chico, where the solar clock was located, is at a geographical longitude of 8º 20’, which means the Sun takes 33 minutes longer to reach here than when passing through the 0 meridian (Greenwich/Castellón), and our geographical location is not in the time zone of the Peninsula but in the next zone of Portugal and the Canary Islands.

Hour correction and the Equation of Time (EoT)

To determine the solar hour from the civil hour and vice versa, one only needs to apply the well-known expression: solar hour = official hour -/+ meridian correction (long. E/W) + EoT - 1h or 2h (daylight saving). Where EoT is the Equation of Time, i.e., the adjustment for the delay or advance of the Sun's passage through the meridian, which varies throughout the year. And minus (-) 1 or 2 hours depending on whether it is winter or summer.

Note: Equation of Time (EoT). The apparent movement of the Sun is not uniform and the duration of the solar day is not constant throughout the year. The difference between the apparent movement of the Sun and the average movement is known as the Equation of Time. Sometimes (the movement) the Sun is delayed when passing through the meridian line and other times it is advanced, and only a few times do they coincide. There are only four days a year in which the solar hour time coincides with the civil hour (average time in the Time Zone / Average Sun / wrist-watch); these days are dates near the two solstices of summer and winter, April 15/16 and August 29/31; very appropriate days to trace or check the meridian line when the variation of the Equation of Time is "zero" minutes. All this could be verified in this Canelas clock. We all know that what rotates is the terrestrial sphere and the stars remain fixed (including the sun), but experts recommend that to understand this subject it is better to consider it the other way around. Also to say that the Sun clock should be called a Shadow clock because the shadow is the hour indicator. And that this clock does not care about winter or summer time changes —You cannot deceive the Sun— as it always invariably marks the "true hour" (verum tempus).

It is surprising that the hours on this clock are modern, each lasting approximately 60 minutes, since in ancient times and throughout the Middle Ages time was measured using unequal hours. Uneven hours include canonical hours; Judaic (biblical) hours; temporary hours (Roman, ancient, or unequal); planetary (astrological) hours; and true hours (natural or solar, which vary according to the EoT — Equation of Time). Hours of equal duration are: Babylonian, astronomical (equinoctial), or modern hours.

The establishment of the current "standard time" (all equal hours) is very recent; it was proposed by the Canadian railway engineer Sandford Fleming in 1870, but it was not until fourteen years later in 1884, at the International Meridian Conference held in Washington, that it was approved. It was agreed to divide the terrestrial sphere into 24 strips, each of 15º, equivalent to 1 hour (24h x 15º = 360º) and established the Greenwich meridian as the starting point (Meridian 0); a unique and universal meridian that gives way to the establishment of Universal Time (UT).

There are several methods for constructing a sundial, some graphic and others analytical, which calculate the projected hour angles on various surfaces when these are not parallel to the Earth's Equator; otherwise (equatorial type clock / sphere parallel to the Equator / axis parallel to the Earth's axis), its calculation is very easy and consists simply of dividing the circle into 24 equal parts of 15º each (1 day / 24h; 360º : 24 = 15º), placing in the center a rod (gnomon/style) inclined with respect to the ground at an angle equal to the "latitude of the place" where it is situated, and orienting it to the geographical N-S (meridian line).

The construction of a horizontal-type sundial, such as the one in Canelas, is somewhat more complex. By the analytical method, the Hour Angle (AH) must be calculated, the result of projecting the hour line of the equatorial clock (of equal divisions of 15º per hour) onto the horizontal plane, which produces different angular hour divisions, but symmetrical with respect to the meridian line. The gnomon (style/rod) is also placed inclined, just like in the equatorial type clock, at an angle "φ" equal to the latitude of the installation site. Note: Placing a "vertical pole" in the ground and marking 24 equal divisions around it with pebbles, as is sometimes seen on beaches, does not function as a sundial for measuring hours. For this to occur, the pole must be inclined at an angle equal to the latitude of the location and aligned with the meridian line, while the ground (the hour plane) must also be inclined at an angle equal to the local colatitude (90° − φ).

OPERATION AS A CALENDAR

A sundial is an image of the solar star's movement, also functioning as a calendar since the length of the shadow (solar height) varies with the declination throughout the annual cycle. Some sundial builders mark the seasons, the months of the year, and zodiacal symbols on the dial.  A surprise of the observation and study of this site was finding "very well determined" fixed 'stones' that marked the main days of the annual calendar. The megalith was chiseled on its three faces to produce a shadow on the ground with a triangular appearance ending in a well-defined point (Pena Bicuda).

Winter Solstice marks and the anniversary of San Martiño

In line with the standing stone forming a N-S central axis, a main stone stands out from the ground (mediatrix stone, meridian, 'stone' no. 5) which was carefully carved in length and height so that the shadow marked three well-defined points. One day a year there is a moment when the tip of the shadow of the standing stone (menhir) at midday (12 solar hour) touches the southern end of the 'stone' and marks February 2nd, Candlemas Day, and also November 11th, San Martiño's Day, days on which the sun has approximately the same declination. Subsequently, after the month of November, the days go by until the shadow reaches the northern end of the same 'stone' and marks the day of the winter solstice, December 21/22 (Nadal/Christmas; longest shadow of the year on the meridian).

Following this, as the days pass, the shadow shortens until it touches the highest central edge of this 'stone' on January 17th, St. Anthony's Day (purification and blessing of animals). But also on this section of the central stone, the shadow is situated on "November 18th", the day of the old patron saint of the parish of Doniños "San Román de Antioquía", which was celebrated formerly on that day; this is because the sun's declination on this day in November is almost the same as on the days close to January 17th (-19º and -20º).

The Summer Solstice and the Equinoxes

'stone' no. 7 (natural rock of the terrain of greater length and height than the hour stones) was trimmed and canteed vertically so that the tip of the shadow marked "exactly" the day of the spring and autumn equinox (March 21/22 and September 22/23); on these dates, the shadow travels in a straight line (E-W) over the ground; the rest of the months it forms the figure of a hyperbola. 'stone' no. 10, measuring 40 cm and very well affirmed in the ground, located on the axis of the meridian line and very close to the standing stone, marks the shortest shadow length of the year at midday (12 h, maximum solar height), i.e., it marks "exactly" the day of the summer solstice, June 21/22. Thus leaving the main days of the annual calendar defined (See figures).

CALCULATIONS. HORIZONTAL SUNDIAL

The sundial must be calculated for the latitude of the specific place where it is to be situated. For the construction of the Canelas horizontal clock, it is important that the ground where it is located is perfectly leveled (which was not the case here). The calculations are performed starting from the hour angle of the equatorial type clock, which are all equal, at 15º per hour.

Analytical methodology and calculation of the Hour Angle (AH) of the sundial

By the analytical method, the Hour Angle (AH) of the horizontal type clock determined by the expression must be calculated. tan AH = (sin φ . tan n) // AH = arctan (sin φ . tan n). Where φ = latitude of the place, and n = 15º, 30º, 45º, 60º, etc. (hour angle of the equatorial clock).

Data: φ = 43.4º // n = 15º, 30º, 45º, 60º, 75º, 90º.  The angles of the first six hour lines are calculated. The remaining ones are symmetrical with respect to the meridian. The angles are measured from the meridian line (12h).

tan AH = (sin φ . tan n) = sin 43.5 . tan 15º = 0.688 x 0.267 = 0.184 // AH = Arctan 0.184 = 10.42º

For the remaining ones: AH = (15º) 10.42º, (30º) 21.65º, (45º) 34.57º, (60º) 49.98º, (75º) 68.71º and 90º. These results correspond very approximately to the actual measurements taken on the ground.

Calendar. For the main dates of the calendar, equinoxes and solstices, the length of the projected shadow on the ground can be calculated, starting from the known data: φ = 43.5º latitude of the place; and the declination δ (of that day); at the equinoxes 0 degrees and at the solstices = +/- 23º 27’; and the height of the gnomon (rod) h = 2.5 m. From the formed triangles, the different lengths of the shadow are deduced.

Length of shadow at summer solstice l1 = h . tan (φ - δ) where δ = +23º 27’ // l1 = 0.90 m

Length of shadow at equinoxes l2 = h . tan (φ) where δ = 0º // l2 = 2.36 m

Length of shadow at winter solstice l3 = h . tan (φ + δ) where δ = -23º 27’ // l3 = 5.86 m

l1 = h . tan(φ - δ) = 2.5 x tan (43.4º - 23.5º) = 2.5 x tan 19.9º = 0.90 m. Same for the others.

(See figures 12 and 13).

ARCA (DOLMEN). PREHISTORIC CHAMBER

Next to the standing stone on the W face was a prehistoric arca (burial chamber/dolmen) of medium dimensions, which was formed by four or five 'stones' firmly embedded vertically in the ground and one more acting as a roof covering them, of which only three were preserved: the back one and the two side ones, with the one closing the entrance and the one covering them missing. The 'stone' on the E side measures 2 m long and 1.15 m high; the one on the W side 1.80 m long and 1.45 m high, and the back one 90 cm long by 1 m high.

The interior of the chamber measures 2 m long and the width at the back is 50 cm, 1 m in the widest part. The structure presents all the characteristics of a small dolmen (arca) and almost the shape of a somewhat irregular cist. Throughout the area of Pieiro and Prioriño, local toponymy records the existence of several ‘arcas’ (dolmens) and ‘lagoas’ (disturbed hollows of prehistoric tumuli), and since ancient times the area has yielded a number of finds, including Neolithic stone axes and other prehistoric tools. The entrance was oriented towards the southwest (winter solstice). Given the characteristics of the aforementioned 'arca', the most probable date for this burial chamber as well as the standing stone (menhir) would be within the Bronze Age in Galicia (1800-700 B.C.) in recent prehistory. (See fig. no. 14).

TOPONYMY OF THE AREA

From this place to the town of Pieiro there are 600 m, to Canelas Beach 230 m, to the Viñas Battery 600 m, to the Prioriño Chico Lighthouse 930 m, to the town of Cariño 1700 m, and to the Castro da Croa de Fontá (Doniños) 3 km. The toponymy of the area is as follows: Praia de Canelas, Cal Feitoso, Pieiro, Praia do Pieiro, Cabo Prioriño Chico, Cabo Prioriño Grande, Entrepieiros, Praia de Entrepieiros, Plagueira, Praia de Plagueira, Espasante, Punta de Espasante, Pieiro Grande, Pedra Alta, Pena do Raposo, Pedra dos Cas, Carricobo, Barquín, As Lagoas, Lagoa Redonda, Cariño, Praia de Cariño, Filgueira, As Chousas, Cómaros, Viñas, Punta de Viñas e O Xunco.

Pena Bicuda. Location of the megalith: Lat = 43º 27’ 64.7” N, Long = -8º 20’ 9.48” W.

HISTORICAL REVIEW OF THE SUNDIAL

The measurement of time has a long history spanning several millennia, so only a few brief points are mentioned here. The Sundial was known in ancient Egypt, Greece, Rome, and China;  the oldest known is Egyptian, a "sechat" bearing the name of Pharaoh Thutmose III and which is more than 3,400 years old. The largest in the ancient world was commissioned by Augustus (Gaius Julius Caesar Augustus, 63 B.C. - 14 A.D., first Roman emperor) to the architect and mathematician Novius Facundus in Rome in the Campus Martius in the year 10 B.C., of large dimensions 160 x 75 m; it was known as the Horologium Augusti. 

The gnomon was an obelisk brought from Egypt 30 m high that projected the shadow on a circular plaza on which "the months and seasons of the year" were marked, according to the length of the shadow at midday (meridian line). Shortly before, 100 B.C., in Athens, the capital of Greece, the Tower of the Winds was built, of octagonal plan with 8 m in diameter and 12 m in height; in the upper part on each face it had a sundial (eight clocks). The eight faces represent the orientation of each wind (compass rose) with engravings of male figures symbolizing them: Boreas (N), Kaikias (NE), Euros (E), Apeliotes (SE), Notos (S), Lips (SW), Zephyrus (W), and Skiron (NW). The Tower was built by the astronomer Andronicus of Cyrrhus (Macedonia). It is considered the oldest public sundial.

The horizontal type sundial (flat clock) was not known on the Peninsula or in Europe until after the 9th-10th century when they were introduced (constructed) by the Arabs in the Andalusian area of the Iberian Peninsula, and subsequently, this knowledge (Arabic wisdom: astronomy, mathematics, etc.) was compiled by King Alfonso X (Toledo, 1221-1284), making it known to the rest of Europe.

In the Middle Ages, although the sundial was known, its use was not popularized until the founding of the Benedictine order in Italy in the year 529 with the Rule of St. Benedict which “establishes the hours of work, prayer and study”. These hours were called “canonical hours / ancient” or unequal hours, which were counted from dawn to dusk. The first sundials began to appear in the 8th century, engraved on the façades of churches, convents, and cathedrals; the Christian Church became the dominant authority in the measurement of time in medieval European society.

The first mechanical gear clocks emerged in Europe in the 13th century; they were very inaccurate and variable in measuring time, to such an extent that very frequently they were regulated using sundials as a guide. Their precision and operation would progressively improve and for a long time they were considered very expensive toys not accessible to the majority of the population. It was not until the 14th century when mechanical clocks with hours that marked “equal” times were built.

At the beginning of the 18th century, portable mechanical pocket watches were still luxury items and sundials and the "midday" bell marking the meridian line in churches (mass clock), convents, or cathedrals were still used. In 1673, the Dutch mathematician and astronomer Christiaan Huygens defined modern time measurement techniques by manufacturing his pendulum clock with an error of less than one minute per day (horologium oscillatorium). Patek Philippe invented the wristwatch in 1868 as a “feminine wristwatch”, designed more as a piece of jewelry than for measuring time; it was improved by the French watchmaker Louis Cartier in 1904, at the request of the aviator Alberto Santos-Dumont, which was the first wristwatch for practical use. As we can see, the widespread use of clocks is historically quite recent.

CONCLUSION

The sundials of the last millennium are not even similar to this one in Canelas; generally of small size (approx. 1 m) in vertical traced with their hour lines engraved or painted and located on the facades of buildings such as palaces, convents, churches, castles and others, both public and private; those made horizontally are of similar characteristics to the previous ones and located on walls, window sills, balconies and on pedestals, and only currently are monumental sundials of large dimensions carried out more for decoration or cultural dissemination than for measuring time in parks, gardens, squares, roundabouts, etc. Since currently universal time is measured with atomic clocks.

The Canelas sundial-calendar (Pieiro de Doniños) remains unknown: who, when, for what and why this secluded place was chosen. Why it was built taking so much effort since the stones weigh quite a bit and they had to be moved, worked and buried one by one firmly in the ground to ensure they did not move, and the distance between them well measured so that the tip of the shadow when passing from one to another correctly marked 1 hour. Regarding the megalith (standing stone / Pena Bicuda), it is possible that its existence was much earlier (prehistoric) than the construction of the solar clock, but it was subsequently conscientiously carved (chiseled) to form a vertical rectilinear and inclined edge with an angle very close to the latitude of this place (43º), and to carve a point so that the projection of the shadow could be clearly visible on the ground.

There is a great contradiction between the modern astronomical technical knowledge that the builder (or builders) is supposed to have had, given the exactness in the measurements of the hour markers and the calendar, and the very rustic construction presented by the 'stones', scarcely worked, almost in a natural state, which seem to be worked with prehistoric stone tools and not iron ones. An enigma that will remain unexplained since there was no type of official archaeological study or excavation.

The location in this area was uninhabited and the nearest residents were the neighbors of Pieiro, Cariño and Fontá (Doniños). Near Canelas, in the place of Viñas (on the seashore), lived in 1652 the Ordinary Mayor of Serantes, D. Antonio Núñez Hurtado and his wife Dª.Juana Fernández de Aguiar, and the 18th-century military batteries of Viñas (1739) and Cabo Prioriño (1799). The megalith and the entire construction have currently disappeared because they were excavated by bulldozers for the construction of the Prioriño Outer Port (in 2002) and in their place a large tank was installed.

Only the photographs taken and the memory of the older neighbors of Doniños, who knew Pena Bicuda from ancient times but were unaware of its use and meaning, remain for history. A pity for this especially interesting monument, of great archaeological and cultural value as well as being the only one known with these characteristics.

CONSULTED BIBLIOGRAPHY

Design and construction of Sun and Moon Dials. Rafael Soler Gayá. C. Ing, Cam. 1997.

Sundials. Construction. Franz Embacher. 1988.

Sundials. History, Construction and Operation. Gin Carlo Pavanello - Aldo Trinchero. 1998.

Book of Solar Clocks. Pedro Roiz. Facsimile, 1575 Edition (Valencia).

Wikipedia.