Spectral Light and Ushnu at Huanaco Pampa

Step 1: Light Comes Through Window
Step 2: Light Reflects off Plastic Cover

Step 3: Spectral Light Appears on Door
The “spectral light” in the title of this post is an event that occurs every January 31^st at our house. The event reminder pops up on our calendar as “Spectral Light on Bathroom Door”. It sounds spooky, but is quite simple. The angle of the sun on this day is such that it comes through an east facing window in early to mid-morning, bounces off a security panel plastic cover in an inner hall way and displays a ghostly light pattern on our bathroom door for a few minutes. The bathroom is on the north side of the house and does not receive direct sunlight. The event is one that lets us think of our house as a big calendar of sorts, our little bit of archeoastronomy in action.

There are several points to mention about this light. First, there must be corresponding event in late November but we have never recorded this event. Second, given that in Seattle the number of days of sun per year is not that great, that our spectral light appears magically in winter is all the more amazing. Third, last summer I was unfortunately only able to spend a hurried morning at the British Museum on the tail end of my Wainwright Coast to Coast Walk, but one display that stuck in my mind was a diagram of the Ushnu at Hunacopampa which showed the position of the rising sun on key dates in the year. In the diagram, the June Solstice, Equinox and the December Solstice are shown. Unfortunately or fortunately, our house was not built around key calendar times, so January 31^st is what we are left with as a house-calendar date.  (Update: 2012-11-08 - we just saw it again today, approximately 42 days before the Solstice.)

Entrance to the British Museum and the Ushnu at Hunacopampa Exhibit

An ushnu is a pyramid-shaped, terraced structure that the Incas used for ceremonial purposes. Sort of a stage and throne rolled into one. Huánuco Pampa (in Spanish) is an Incan site that dates from 1470 to 1532 AD. The Huánuco region is in central Peru and served as an Incan administrative center. The role of astronomy at ushnu at Huánuco Pampa is discussed at the Universidad Nacional Mayor de San Marcos - Universidad del Perú web site.

Our house was remodeled in 2005-2006. Two changes we made make the spectral light event possible: a small bump out where the east-facing window is and the enlargement of a passage way. What if we had taken archeoastronomy into account when we were remodeling? The four most expensive words in remodeling: “While we’re at it…”
The Light Path Through the House