Summer moonrise

A unique astronomical event occurred on the evening of June 17th, 2000, at the Standing Stones in Baltray. With the Summer Solstice sunset occurring in the northwest, the full moon was rising in the southeast, quite close to the point of the Winter Solstice sunrise. The large stone at Baltray marks Winter sunrise and Summer sunset.

The Winter Solstice sun rises about 130-131 degrees in the southwest on December 21st. The moonrise on June 17th, 2000, was at 129.5 degrees of azimuth, quite close to the winter sunrise position, on which the large monolith at Baltray is aligned. The island of Rockabill, on which is built a lighthouse, forms the other end of the alignment.

Unfortunately on this occasion there was some cloud on the eastern horizon despite generally clear skies overhead. This meant we could not record the actual rising position of the moon, but as can be seen from the above picture, the moon's position is nearly coincidental with that of the Winter sunrise. For this photo I was positioned about 30 feet northwest of the large stone, so we are viewing it almost edge-on.

Moonrise at Rockabill from Baltray

In this close-up photo of the event, the light of Rockabill lighthouse can be seen (arrowed), as can the moon which is rising out of the clouds. Although the Winter sunrise occurred originally at Rockabill as viewed from here, it now rises two sun-widths to the north, or left, of Rockabill because of the slow shift of precession. Nevertheless, the alignment of the standing stone on these astronomical events is still quite accurate.

Moonrise at Baltray

In this photo the moon is beautifully framed by a cut-off in the top of the standing stone. Note also the lovely pale reflection of the moonlight on the surface of the sea.

We sought the opinion of a local archaeologist in putting a date on the erection of the Baltray standing stones. Although there is some debate as to whether standing stones were erected in the early or late Bronze Age, the archaeologist told us that a date of around 2000BC is generally accepted as the date of their construction.

Despite the initial cloud problems, it turned out to be a glorious event, with the veiled moon showing pink and orange colours behind the thin clouds. It was a very warm night, and even after the 10:30 (approx) moonrise, most of the seven people who were there to observe the event stayed until almost midnight.

Thanks go to Victor Reijs, of Geniet, who provided GPS data for our exact location on the night.

TECHNICAL INFORMATION:

Moonrise, June17th, 2000:
Local Information: Position (epoch of date): RA: 18h 33m 43.49s Dec: -22° 27' 12.3" Altitude: 00° 02' 07" Azimuth: 129° 16' 45" U2000: Chart 340, Vol 2 Rise: 22h 23m 01s Transit: 01h 30m 12s Set: 05h 29m 48s. Geocentric Information: Position (epoch of date): RA: 18h 31m 48.08s Dec: -21° 40' 24.7" Constellation: Sagittarius. Phase: 0.992 Diameter: 1766.03" Phase Angle: 10.5°. Elongation: 169.5°.

Moonrise positions for the Boyne Valley:
See also a listing of all the full moon rising positions for the Boyne Valley for 2000 and 2001 in our astronomy section.

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Notice: All pictures, except where otherwise stated, are copyright of the author, Anthony Murphy. For more information on any of the images, contact me at

mythicalireland@eircom.net