On Wednesday, March 20 there will be another public pilgrimage to the Pen Henge standing stone array at the top of Munson Mountain, this time to mark the arrival of the vernal equinox. The Pen Henge stones delineate the sunset points on the four cardinal dates of the year. Anchored by the Heel Stone, the equinox stone points to the sun's sunset point at both the Spring and Fall Equinoxes, while the other two stones mark the winter and summer solstice setting points respectively.
As with previous events, members of the Okanagan Centre of the Royal Astronomical Society of Canada welcome members of the public to join them for the observance which will mark the halfway point of the Sun's annual migration.
If clear skies permit on March 20, participants will be able to watch the shadow cast by the setting sun creep slowly from the equinox stone to align perfectly with the heel stone. The equinox gathering will begin around 6 p.m. in preparation for the actual sunset which will occur around 6.35 p.m. PDT. The actual moment of vernal equinox will have taken place at 4.02 a.m. that morning.
Leading the OC RASC observance will be OC RASC Penticton vice-president Ryan Ransom who will be joined by other club members who will set up safely filtered Sunspotter telescopes to allow solar viewing by the public.
The Pen Henge project was conceived in 2009 during the International Year of Astronomy (IYA) by members of the Okanagan Astronomical Society which is now part of OC RASC. The project was aided by the active support of Penticton City Council and Parks Supervisor Jeff Lynka.
Photos of the array and earlier observances can be viewed on the OC RASC website at www ocrasc ca through the Image Gallery link and the Pen Henge folder.
Chris Purton, a retired scientist at the Dominion Radio Astrophysical Observatory at White Lake who spearheaded the Pen Henge project noted, "For most of the year the structure simply illustrates the enormous range along the western horizon where the sun sets. Most people subconsciously know of this, but they are quite fascinated to see the idea laid out so graphically."
A brass plaque with a brief explanation of the array is permanently attached to the top of the heel stone.