Pages from a Dialist's Notebook - An Indoor Analemma

In the fall of 1995 I moved to a new home where I placed my office in a room high in the north east corner of the building. The room has a large east-facing window through which the sun came - suddenly and brightly - each morning at about 7:30. At first I found this annoying, but then I realized I could take advantage of the situation and project an 8:00am analemma which would demonstrate the Equation of Time. Preliminary observations indicated that the analemma would wind its path across the walls, furniture and floor on the west side of the room.

I mounted a cardboard arrow high on the east window for a gnomon, and each morning at 8:00 I placed a small Avery dot where its shadow fell at Standard Time. My first dot was placed on the 1995 winter solstice. During the winter the analemma snaked its way across the north wall, through a bookcase, and onto a filing cabinet on the west wall.


It made it! - this depiction 12-21-1996, the winter solstice
Drawing of an Analemma
Click in the drawing to see a color version.

The morning of the vernal equinox was clear and sunny. I placed dots at 5 minute intervals following the path of the shadow as long as the sun entered the room.

I realized from the Loss Of Sun on the equinox that I was in for some damage control. An eave overhanging the window was going to block the sun during high summer. Also, the point where the loops of the analemma crossed was going to come right where the shadow dropped off the filing cabinet and into the closet.

I decided to plot the smaller, summer loop with a second gnomon 10 inches below the first. This had the effect of moving the loop out into the room where it makes an interesting conversation piece. The effect of lowering the gnomon is not obvious in the drawing.

On the morning of the summer solstice, I again traced the path of the shadow, this time into and out of the closet, then across the floor. Here is a photograph of the small loop taken a few days after the summer solstice. The photo also shows a portion of the path of the summer solstice shadow as it moved across the floor.

The journey through the autumnal equinox and back across the filing cabinets was uneventful, and eventually the shadow crept up onto the north wall.

Although the morning of the winter solstice was cloudy I had already placed enough dots to indicate that analemma had found its home, and the year-long project was successfully completed.

The timing for the placement of the dots was provided by The Dialist's Companion, a program written by Fred Sawyer and myself recently published by The North American Sundial Society.

Analemma started 12-21-1995. Drawing started and put on line 6-22-1996.
Drawing updated 7-6, 8-21, 9-24, 10-16, 10-30, 11-10, 11-23, 11-30, 12-9, 12-21 of 1996

Bob Terwilliger

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