mega-what.com

Glossary

Most mega-what pictures show views from a monument with added prehistoric luni-solar trajectories. Those two pages explain the solar and lunar notation used in the pictures and the concepts behind it.
More general information may be found in the FAQ.

Site descriptions start with a header of the form:

Townland: Monument_type  SMRno

NGR

Townland: Is a long standing and vital part of any rural Irish address, referring to a fairly restricted area loosely based on agricultural productivity. Elsewhere, the nearest named geographical region is used.
Monument_type: Name of the morphological class that the monument has been ascribed to.
SMRno: The Sites and Monuments Record number officially identifies the site and its location. Two letters ("CO" if not given) indicate the county (CO=Cork, KE=Kerry). Then, the first three digits give the county 6" Ordnance Survey map sheet number. The first three digits after the hyphen are the site number on that map and any subsequent digits refer to individual components of a complex site. In published hardcopy these trailing digits tend to be in the range 01-99 but in the online register are 001-999. Click here to access the on-line register. The SMR number has been renamed. It is now the RMP number (Record of Monuments and Places). For U.K. sites the NPRN number is given.
NGR: National Grid Reference (Optionally followed by GPS co-ordinates).

Note that distances between sites as given on individual pages are "as the crow flies" but distances on the ground may be much longer.

Glossary: mega-what terminology

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AppDec: Used in the data tables where it means Apparent (observed) Declination, corrected for atmospheric refraction using a standard formula. This correction enables standard comparisons. Atmospheric refraction, which varies with temperature and pressure, bends the path of light from distant objects upwards. The difference is more than 1/2 degree at the horizon but decreases to zero for anything that is vertically overhead. This means that, when the sun is observed to have risen, it is actually still below the horizon! For naked-eye astronomy of the sun, planets or stars, there is nothing else to worry about but the moon requires a further correction for Horizontal Parallax.

Archaeoastronomy: A relatively new discipline concerning the study of old astronomies.

Axis / Axial: An imaginary line bisecting a monument, usually along its longest dimension. / Direction along an axis. The Irish Stone Circles in this study have an Axial Stone (the position of which defines the axis) and are known as Axial Stone Circles.

Az: abbreviation for Azimuth: The direction of an object measured as a horizontal angle clockwise from true north. [Diagram]

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Boulder-Burial: Monument type unique to Ireland. Large boulder set on top of three or four smaller stones, which may not be visible. All four excavated examples covered a pit or ritual deposition but traces of human bone were found at only one. More

Bronze Age: Period from the first use of copper tools to the introduction of iron. In Ireland, from about 2400 BCE to 600 BCE.

Celestial Equator: An imaginary projection of the earth's equator into space. As the earth spins, the sky appears to rotate above a stationary earth. Every point on the celestial equator passes directly over every point on the earth's equator every day.

Cork-Kerry Stone Circle Complex: Bronze Age monuments such as axial stone circles, short stone rows, boulder-burials and Standing Stones, often found in close proximity and predominantly in the two named counties of Ireland. More

Cross-Quarter: A cross-quarter day is a day half-way between a solstice and an equinox.

Their dates were all moved to 1st in the Gregorian calendar but they are more accurately on or about Feb 3rd, May 5th, Aug 7th & Nov 6th. Commonly held to be survivals of the Celtic calendar, these festivals are clearly much older. See Prehistoric Solar Calendar. There are four cross-quarters. With the four quarter days (two solstices and two equinoxes) they divide the year into eight parts.

Dec: abbreviation for Declination: The angular distance of a celestial object North or South of the celestial equator. Reckoned positive when North and negative when South, the declination of a celestial object is exactly equivalent to the latitude at which it would be seen to pass vertically overhead. [Diagram]

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Eclipse: Eclipses occur when the sun, moon and earth are all in a line. For this to happen the moon must be near a node of its orbit. A solar eclipse occurs when the moon gets directly between an earthbound observer and the sun. A lunar eclipse occurs when the moon passes through the earth's shadow cone and is thus, unlike a solar eclipse, visible from an entire hemisphere of the earth. See Fred Espinak's Lunar Eclipses for Beginners.

Eclipse Prediction: Traditional western astronomy has used the Saros Cycle, based on the fact that eclipses repeat in similar patterns after 18 years 11 days. This was discovered by the Babylonians in the fifth century BCE as a result of written record keeping. The megalithic astronomers of North-West Europe seem to have used a different system, developed much earlier, in which both the annual solar and the 18.6 year lunar nodal cycles were measured along the horizon and divided into sixteenths See the Megalithic Solar Calendar & Lunar Calendar. There is a direct relationship between the two cycles and, for the purposes of eclipse prediction, the sixteenths may be regarded as centres of periods. Determination of the moon's place in its cycle predicts the equivalent solar periods within which any eclipses must occur. See Prehistoric Eclipse Prediction.

Ecliptic: The plane of the earth's orbit around the sun. The earth's axis of rotation is not perpendicular to the ecliptic but tilted. See Obliquity of the Ecliptic.

Equator: A great circle round the "middle" of the earth's surface that is equidistant from its poles and divides it into the northern and southern hemispheres.

EQ: abbreviation for Equinox: The day when the sun crosses the equator and day and night are of equal length. This happens twice a year - at the spring equinox (around March 21st) the sun's daily motion along the horizon is from south to north, while at the autumn equinox (around September 21st) it is from north to south. See Prehistoric Solar Calendar.

EventDec: The calculated theoretical declination of a specific celestial/calendrical event.

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Five-Stone Circle: An Irish axial stone circle consisting of five stones. Typologically distinct from the larger multiple stone circles and generally later in date. Thought by some to be a degenerate form indicative of a waning culture, the survey evidence shows that their siting criteria were often more sophisticated even if the manpower required to erect them was less. They might represent an early example of the minituarisation that comes with advanced technology.

Horizon Astronomy: Using the horizon to measure the rising and setting positions of celestial objects. In the nineteenth century, the Hopi of North America were documented as measuring the sun's position in this way for calendrical purposes. Now, thanks to Whole Horizon Analysis, it is clear that early North-West Europeans did the same but had an even more sophisticated system for making solar and lunar observations, enabling eclipse prediction.

Horizontal Parallax: Makes the rising or setting moon appear to be further south (when viewed from the northern hemisphere) than it really is. This is because the moon is close to the earth (compared with the sun) so that the observer's distance from the equator (also the ecliptic) becomes significant. North-west Europe is quite far north of the equator and so, when the moon is near the horizon, we are in effect looking down on it rather than straight at it. It therefore appears to be further south than it actually is. Mean Lunar Horizontal Parallax in south-west Cork is about 0.8 degree at the horizon but its exact value depends on latitude and horizon altitude. In the data tables, LunarDec = AppDec - Mean Lunar Horizontal Parallax.

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Int: abbreviation for Intersect: Used in the data tables. Refers to the horizon notch created by the intersection of landscape features at different distances from the observer.

Ish: Found in the data tables, appended to the name of a target point on the horizon. Means that the measured position cannot be guaranteed as accurate. This is usually due either to vegetation or to the landscape feature itself not having sharp definition. Even so, the possible error is usually only a small fraction of a degree.

Latitude: Angular distance, north or south of the equator, of a point on the earth's surface.

Limb: The apparent edge of the sun or moon.

lunar nodal cycle: By this, the 18.6 year lunar Node cycle is meant. The lunar orbit is at 5.15° to the ecliptic and the two points where it crosses the ecliptic are the nodes. Eclipses can only happen when the moon is near a node. The whole lunar orbit rotates round the earth once in 18.6 years, thus the position of the nodes does the same. This orbital rotation also effects the rising and setting positions of the moon. In particular, the positions of the lunistices vary in a predictable manner over the 18.6 year cycle. [See Major Standstill, Minor Standstill]. This cyclical motion along the horizon is an indirect pointer to the position of the nodes and was used as such by the megalithic astronomers as an aid to eclipse prediction, although their knowledge was empirical and does not imply any theoretical understanding.

LunarDec: abbreviation for Lunar Declination: The calculated theoretical declination of a lunar event OR, in the data tables, the AppDec of an observed point adjusted for Mean Lunar Horizontal Parallax to give an approximation of the moon's declination for that position after adjustment for atmospheric refraction.

Lunistice: The lunar equivalent of a solstice. When the moon is at its most northerly (+) or southerly (-) declination of the month, that is, when it is at 0° Cancer or 0° Capricorn. More practically, the moon rise or set nearest to those positions. More.

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Major Standstill (Max): A time when the Lunistices of the moon are rising and setting at their furthest horizon distance from the Equinox. Their monthly positional shift along the horizon is at a minimum, hence the term standstill. The ascending node of the lunar orbit is at or close to 0 degrees Aries. Thus the declination of the lunistices both north (+) and south (-) is equal to the angle of the obliquity of the ecliptic PLUS 5.15° (the angle of inclination of the lunar orbit). [Diagram]

Megalith: "Great stone", from the Greek.

Prehistoric Lunar Calendar.

Prehistoric Solar Calendar.

Minor Standstill (Min): A time when the Lunistices of the moon are rising and setting at their shortest horizon distance from the Equinox. Their monthly positional shift along the horizon is at a minimum, hence the term standstill. The descending node of the lunar orbit is at or close to 0 degrees Aries. Thus the declination of the lunistices both north (+) and south (-) is equal to the angle of the obliquity of the ecliptic MINUS 5.15° (the angle of inclination of the lunar orbit). [Diagram]

Morphological classification: Classification of things (archaeological monuments in this case) by similarity of physical form.

Multiple-Stone Circle: An Irish axial stone circle consisting of seven or more stones.

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Neolithic: The New Stone Age. In Ireland, from the introduction of agriculture at perhaps 5000 BCE to the earliest use of metals round about 2500 BCE.

Node: One of the two points where the lunar orbit crosses the ecliptic. See lunar nodal cycle.

Obliquity of the Ecliptic: The earth's axis of rotation is not perpendicular to the ecliptic but tilted. Thus the angle between the equator and the ecliptic is the same as the angle of the earth's tilt. This angle, known as the Obliquity of the Ecliptic, is currently about 23.4° but in 1800 BCE it was about 23.9°. [Diagram]

OBT: abbreviation for Obscured By Trees!

OD: abbreviation for Ordnance Datum: Height above sea-level as defined by the Ordnance Survey.

OS: abbreviation for Ordnance Survey.

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Pair: abbreviation for Standing Stone Pair:  More

Passage Tomb: A chamber, usually with a passage leading into it, originally covered by a circular cairn. Usually built on high ground, though rarely on summits, often featuring "passage grave art". Probably 300 or more in Ireland, mostly in the northern half, and the earliest of the Neolithic tombs. Found all along the Atlantic seaboard, from Iberia to Scotland, Scandinavia and Denmark.

Portal Stones: Upright stones either side of an "entrance". From porta, Latin for gate.

Portal Tomb: The simplest type have a single large capstone set, often at a significant slant, on top of two large portal stones and a smaller back-stone. May have additional side-stones and/or a smaller, secondary capstone at the rear end. Regarded as Neolithic, there are over 160 in Ireland - mostly in the northern half. Also found in Wales and Cornwall.

Row: abbreviation for Short Stone Row: A row consisting of three to six Standing Stones.  More

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SMR: abbreviation for Site and Monument Register: The Irish state register of sites and monuments. Now called the Record of Monuments and Places. Click here to access the register on-line.

Solstice: A time when the sun is at its furthest from the equator and seems to pause before beginning its return. Day and night are at their most unequal and the declination of the sun is the same as the Obliquity of the Ecliptic.

Ssol: abbreviation for Summer Solstice: The sun reaches its maximum north (+) declination at the summer solstice which is the longest day in the northern hemisphere. Currently this happens around June 21st. See Prehistoric Solar Calendar.

Standing Stone: The most basic megalithic monument, consisting of a single stone set upright in the ground. More

Stone Circle: An approximately circular arrangement of spaced Standing Stones. The Irish Stone Circles considered here are known as Axial Stone Circles. The "Axial" stone is usually found in the south-western quadrant and emphasised by being the lowest stone in the circle, commonly being wider than it is tall. It indicates an axis of approximate bi-lateral symmetry because opposite it are a pair of portal stones and the arcs to either side contain the same number of stones.  More

SXQ: Abbreviation for Summer Cross-Quarter: A day when the sun is half-way between an Equinox and the Summer Solstice. Either Beltane or Lunasa. Currently about May 5th & August 7th. See Prehistoric Solar Calendar.

Technical Notes on the Pictures

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Whole Horizon Analysis: Techniques pioneered by the author to analyse the whole horizon (rather than just monument axes) for potential correlation with astronomical phenomena.

Wsol: abbreviation for Winter Solstice: The sun reaches its maximum south (-) declination at the winter solstice which is the shortest day in the northern hemisphere. Currently this happens around December 21st. See Prehistoric Solar Calendar.

WXQ: Abbreviation for Winter Cross-Quarter: A day when the sun is half-way between an Equinox and the Winter Solstice. Either Imbolg or Samhain. Currently about February 3rd & November 6th. See Prehistoric Solar Calendar.

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© Michael Wilson.