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Established 16/3/2000

Dowth North aligned on Minor Standstill moonset

Passage also accepted beam of sunlight on November-February Cross-Quarter Day

In her 1969 plan of the northern passage of Dowth, Clare O’Kelly worked out the magnetic bearing of Dowth’s northern passage using a line centred on the rear orthostat of the central recess of the chamber passing through the centre of the distance between the two outermost passage orthostats — L1 and R1. This line is marked on the plan below as line (A).

Dowth North plan with azimuths

The orientation of the northern passage of Dowth is given as 250 degrees magnetic azimuth in Clare O’Kelly’s 1969 drawing. This may be an old survey, but the alignment of Dowth North has been confirmed by another recent survey. The results point towards the possibility that this passage was, in fact, oriented towards the setting position of the Moon for minor standstill south setting in c3300BC. When the plans were drawn in the 1960s, magnetic north was used rather than true north. According to F. Prendergast and T. Ray ("Ancient Astronomical Alignments: fact or fiction?", Archaeology Ireland, Summer 2002), the angular difference is large since magnetic north at the time the plans were drawn was 12’ west of true north.

So, in order to correct for this error, we must subtract 12 degrees from the magnetic reading, which according to O’Kelly is 250 degrees. This gives us 238 degrees (True), which is bang on to the Minor Standstill South setting moon for the epoch c3300BC. Using SkyMap (v7), I worked out the azimuth of Minor Standstill setting for c3300BC at almost exactly 238 degrees azimuth, based on a declination for the moon of -18 degrees 45 arcminutes. (*Note: This is a geocentric azimuth. Correction for topcentric, or local, azimuth, due to parallax means the Minor Standstill setting may have been as much as a degree south of this azimuth. See Victor Reijs' page for explanation. Even with this one degree of difference, it would not make any change to the conclusion that Minor Standstill would still shine into the central recess of Dowth North, providing the survey data is accurate).

Based on a flat horizon, and with the correct latitude and longitude for Dowth, that would be the modern equivalent of November 16th sunset. That sunset, as confirmed by observations and photographs by myself and Anne-Marie Moroney, would put a half-visible sun sitting over the entrance of Newgrange - i.e. over the part which, viewed from Dowth, would contain the milky quartz.

Nov 14th sunset from Dowth over Newgrange

Sunset on November 14th photographed from the top of Dowth looking at Newgrange. It is hard to see the actual disc of the sun, but subsequent observations showed the Nov. 16th sunset sets over the entrance to Newgrange.

The range of azimuths allowed by the passage in its current state is shown in the plan at the top of the page. The northernmost azimuth covered is 245 degrees, which almost certainly would allow the sunset on the November-February (Samhain/Imbolc) Cross Quarter Day to shine onto Chamberstone 13 (C13 marked on plan). This northernmost azimuth is marked with the line (B), and the beam itself would have lit up the side of a beautifully carved chamberstone, C19 (Photo on right, see First Light illustration below). The southernmost reach of the range of azimuths is 231 degrees T, which is only a few degrees from Winter Solstice sunset (Line (C)).
Chamberstone 19
 

Chamberstone 19, Dowth North

 
First Light at Dowth North

First flash, last flash at Dowth North

Using SkyMap to bring us back to the 3300BC epoch, I calculated the approximate dates when the sun would begin to shine into the chamber of Dowth North and when it would shine for the last time during its southward run along the horizon towards Winter Solstice. The "first flash" event (illustrated on left), when the sun beam first enters the chamber, occurs at 51 days before Winter Solstice, which would be around the old Samhain cross-quarter event (November/February Cross-Quarter).

The "last flash" occurs just 23 days before Winter Solstice. At this time, as the sun nears Winter Solstice and the beam withdraws from the passage of Dowth North, the Winter Solstice beam would be striking off the chamberstones of the southern passage. (See picture on right).

Perhaps the northern passage was used in conjunction with Dowth South to watch the sun's slow progress towards Winter Solstice. In other words, as the sunbeam retreated from Dowth North in the few weeks before Winter Solstice, the beam in Dowth South would be strengthening and illuminating chamberstones C7 and C8. (See plan). This idea has been discussed on the Irish-Stones list, and was first brought to my attention by Charlie Scribner.

Of further significance is the apparent alignment of the central axis of the recess chamber which is accessed from the south recess of the main chamber. This alignment is marked Line (D), and is very close, within a degree and a half, of the sunset position on the May/August (Bealtaine/Lughnasa) cross-quarter day. Because of the wide sweep of this off-chamber, it is more than likely that the Minor Standstill North setting was also a target. It is possible this chamber existed before the rest of Dowth North was built, as part of a smaller site. At Knowth West, the innermost part of the passage is oriented differently to the rest of the passage, and perhaps the builders had a different intent originally. See this page for more details.

Sunbeam in Dowth South

The sunbeam in the chamber of Dowth South around the time of Winter Solstice.

This is not a definitive explanation of Dowth North’s orientation, because the outer part of the passage was probably removed during early Christian construction there which saw the additon of a complex souterrain structure which interfered with the original Neolithic structure. Based on the extant passage, it would seem there is a distinct possibility the passage pointed to the Minor Standstill south setting Moon, while it also accepted sunlight on the November/February Cross-Quarter Day which would have illuminated chamberstone 13 (C13).

It is highly probable that an observer, standing in the rear recess of Dowth North looking out through the entrance (barring present-day obstacles) of that passage could see Newgrange in his/her field of view. This is interesting because the central axis of Dowth South points to the Hill of Tara and is oriented towards Major Standstill moonset. So both passages appear to have a central axis which points to either major or minor standstill setting moon, and both of these moonsets occur over other significant ancient sites - Newgrange and Tara.

Anthony Murphy, November 30th, 2003

Back to the Dowth page

Pages of interest:

Winter sunsets: the Winter Solstice event at Dowth as recorded by Anne-Marie Moroney.
Inside Dowth: Dowth's southern and northern passages explored.
Dowth damaged: An 1849 RIA excavation caused major damage to the mound.

Acknowledgements:

I would like to personally thank Anne-Marie Moroney for her patient work studying Dowth, and particularly for her assistance in finding the Dowth South-Tara alignment. I would like to acknowledge the very welcome input of Victor Reijs and Phil David, and for the usual 'peer review' from the Irish-Stones group. An article highlighting the probability of a Samhain Cross-Quarter Day alignment of Dowth North, by Gillies MacBain, was published in "The Pulse" newsletter in Samhain 2000.

All information and photos, except where otherwise stated, copyright, © Anthony Murphy, 1999-2015
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