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General info > Method - Observatories - Geometry - Date-lines - Precession

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Observation method

Megaliths are often useful to observe movements in the celestial sphere.

Warning Megalith's usability as observatory does NOT prove they where intend to! 


Observations using a alignment

An alignment (a row of standing stones) can be used to observe certain point on the horizon, for example the point of sunrise on a specific moment like midsummer solstice. A combination of lines of view can be used as calendar.
Also movements of the Moon, planets and stars can be examined using an alignment. Farther standing stones and remarkable landscape points can be used as lines of view.

Lines of view (figure)


Observations using a stone circle

A stone circle of course gives more possibilities; it can be used to construct a year calendar...

 Sun positions (figure)

The angle 'X' (figure above) is determinate by the observatory's degree of latitude. More northwards the angle "X" will be greater, more southwards 'X' will be smaller. The same stone circle can also be used to mark the points of sun set...

Around midwinter and midsummer during a week the sun seems to rise (or set) on the same point. This phenomenon is called the 'solstice'. This is a consequence of the Earth's elliptic orbit around the Sun.


"Observation tunnel"

Many chambered tombs are like a tunnel, sunbeams can only reach the chamber on specific moments, for example Newgrange (Ireland), where the sunbeams bring light into the chamber on winter solstice.

Entrance tomb Newgrange
Entrance tomb Newgrange

So using a long tunnel we can make a date marker. If the tunnel is directed east, to the spring-equinox (around March 21) than also the sunbeams shall light the tunnel during autumn-equinox (around September 23)
Well known as a "spring-equinox-marker" is Cairn 'T' in Loughcrew, Ireland.
Of course also other dates can be marked, if the tunnels is built in another direction.

An arrangement positioned to the south could also be used, because the Sun's maximal ascension (noon) changes during the year. During midwinter the Sun's ascension above the horizon is lowest, the highest ascension is reached at noon around June 21. A southwards arrangement gives the discomfort of the blinding sunbeams, dangerous for the observer.
In an arrangement directed to the point of sunrise or sunset, the sunlight won't be to strong, but early in the morning the observation can be by troubled by fog.


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Page published November 21, 2015

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