Glossary - The Stones and the Stars: Building Scotland's Newest Megalith - page 308

a large, horizontal stone between two vertical uprights, possibly so that
the southerly Moon can appear to roll along the top of the horizontal
stone.
Regression of the Lunar Nodes The westward motion of the nodes
where the Moon's orbit crosses the ecliptic, as the orbital plane precesses
in space due to the pull of the Sun and of Earth's equatorial bulge. Each
complete circuit of the ecliptic by the nodes takes 18.61 years.
Right Ascension The equivalent of terrestrial longitude, projected onto
the sky, and measured in hours and minutes from the vernal equinox,
q.v.
Samhain Celtic harvest festival, October 31 to November 1.
Sarsens Tertiary sandstone boulders brought from the Marlborough
Downs, 20 miles north of Stonehenge, and used in the construction of
the Stonehenge III lintels and trilithons; also for the stone circles at Ave-
bury.
Silbury Hill A conical artificial hill erected near the site of the Avebury
complex around 2700 b. c. The construction technique is analogous to
the one used for the stable Egyptian pyramids, 2650 to 2500 b. c. Excava-
tions have found no interior chambers or burials within Silbury Hill.
Skara Brae A Neolithic village of nine stone huts on the largest island
of Orkney, built around 3200 b. c. and abandoned around 2400 b. c., bur-
ied by sand and uncovered by a storm in 1850.
Solstices The dates in the year when the Sun reaches its most northerly
and southerly declinations, around June 21 and December 21.
Standstill One of the two occasions, in the 18.61-year cycle of the regres-
sion of the lunar nodes, when the Moon reverses its monthly shift in dec-
lination. At major standstill the Moon at its furthest north for the month
rises to the north of the midsummer Sun, and at minor standstill 9.3 years
later it rises to the south of it at the corresponding point in the month,
both times with a corresponding southerly extreme 14 days later.
Temple Wood A site in Kilmartin Glen, Argyllshire, with large stand-
ing stones that Alexander Thom believed to be the most sophisticated
lunar observatory in the British Isles. There's also a large, but low, stone
circle with a bed of selected stones and a central kist.
Trilithon A free-standing structure of three stones, two upright and the
third forming a lintel across them. The larger inner structure of Stone-