The Summer Solstice

The shadow at roughly 12:10 on June 21

The shadow at 12 noon on June 21

It was with great excitement I awaited the noon hour on June 21 to observe the way the sun fell upon the house. In particular, I was anxious to see how the sun lay upon the sunburst pattern on the south gable of the house.

To my minor disappointment the sun at high noon was just slightly off from dead center on the triangle, but what made me quite happy was that at roughly 12:10 the shadow was centered on the roof, but also that the only aspect of the sunburst not in shadow was the sun shape itself. I couldn't have hoped for a better outcome. It thrills me that without aid of a calendar I could, in essence, look up at the house around this time of year and tell you when the longest day of the year has been reached.

I suspect that the reason the shadow is not centered at noon is because the house is not dead-on south. Does anybody have any perspective on that? I'd be curious to know.

Any guesses as to where the shadow will fall at the winter solstice?

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Update
I received this from my father-in-law Lou, who is a former physics and astronomy teacher:

Dave,

You should not expect the sun to match your triangle at exactly 12 noon because in the eastern time zone it is 12 noon everywhere from Boston until almost Chicago. The sun cannot be due south in Boston and Chicago at the same time. You are in the eastern part of this time zone, so I would expect the sun's peak on your house to match your triangle peak before 12 noon. My memory is that the match occurred at 12:10. This surprises me. Do you know with certainty that that side of the house faces due south? How accurate is your watch?

It is a mystery worth solving.

Lou

My reply:

I'm sure my watch was accurate, at least within a minute or so. I suspect the issue is that the house is probably not on in alignment with the north-south axis. It'd be interesting to find out how far off it it is. When I did the foundation layout I referenced south with a hand-held compass that gave me a general sense of the line. While doing the layout I was also trying to take into account the axis of our garden which is very close to south, so I probably tweaked the line a bit to make it a compromise between the two factors.