
Observation of the skies has now shown that the Mound on Windmill Hill was deliberately located to observe the Winter Solstice sunrise. When seen from the Mound, the southernmost, lowest appearance and subsequent ascent of the Sun is precisely defined by the steep northern flank of the Tor. Today the midwinter Sun rolls up the side of the Tor, but in approximately 3000 BCE, only the top rim of the Sun was visible in the notches created by the terraces. The calendrical precision the terraces provided would have allowed for accurate observation of the Winter Solstice from the Mound—without blinding the observers.
When seen from the Mound, the Sun at Winter Solstice not only rises up the Tor and reaches its zenith over Chalice Hill, it also sets over the western end of Wearyall Hill. Thus the Mound provided the viewing platform to look over the entire island and relate it to the sky. Prehistoric observers on the Mound used other points on the Tor, and many points on the horizon (some natural, some human enhanced), to observe all the solar and lunar extremes. The sky-watchers who came to the Isle of Avalon may have placed wooden posts along the back of the Tor to watch the movement of the stars in the slow rotation known as the precession of the equinoxes. They could even have forecast a momentous event towards the end of the fourth millennium BCE, when the heliacal rising and setting points of the brightest star in the sky, Sirius, were the same as those of the midwinter Sun. Amazingly, in that era, the entire Milky Way was visible; providing a brilliant ring of light just above the horizon.
The Mound may have been built very early on in the sequence of British mound building perhaps as early as the fourth or even the fifth millennium BCE. The natural features of Avalon, its prominent hills set in a level plain, coupled with the Mound, would not only have assisted in the development of astronomical practices but also in the growth of the whole social, mythic and spiritual context in which they were embedded. The island must have hummed with the life and activities appropriate to a Holy Isle – an Isle of Earth certainly, but also an Isle of the Sky.
The Mound still functions today: clicking off the solstices, marking the lunar extremes, indicating the great procession of the stars through the heavens, linking earth and sky into the one dance. And over the next few decades the Mound will continue to indicate on its major alignments the co-incidence of the Solstitial Sun’s risings and settings on the crossing points of the Ecliptic and the Milky Way.
Between 1980 and 2016 CE the diameter of the Sun at each Solstice passes over the exact crossing points of the Ecliptic and the Milky Way. The Sun does this approximately every 13,000 years in the slow rotational movement known as the precession of the equinoxes, but the current event will not repeat for over 26,000years. The Sagittarius / Scorpius crossing or portal, identified by us in the heavens with Gwythyr ap Greidyawl, points to the heart of our galaxy, the Milky Way. The Gemini / Orion Portal, identified by us with Gwynn ap Nudd, points out of the galaxy. Thus the Winter Solstice Sun will exactly mark the galactic core until about 2016 CE. (Source: The British Mystery School Of Avalon)