Astronomical Musings: What day is Pixar-Henge day?

I’ve had a couple of conversations with Tom over the last couple of days, and they were curiously related. He just got back from a trip to Ireland where he visited Newgrange, a prehistoric tomb mound in County Meath. It actually predates the Great Pyramid at Giza, and predates Stonehenge by a thousand years.

One of its interesting feature is that on the date of the winter solstice, the rising sun illuminates the entire length of the main passage, providing 17 minutes of light to the inner chamber. Pretty neat. A lottery is apparently held each year for tickets to view this event (thousands apply, a couple of dozen are allowed to view).

Anyway, in a separate conversation, Tom announced that today, a similar event happened at Pixar. Our main building has a long corridor that runs east to west, and apparently this morning (May 6) was the date in which the rising (and setting) sun appears at the eastern (western) end of the corridor, and illuminates the entire hall.

So, Tom asked: “What’s the equivalent date when we can view this event again?”

A few minutes of thought told me that however many days we are away from the summer solstice, I could solve that if I could do add and subtract dates in my head, or by counting dates on a calendar, but I decided to use the pyephem library instead. I didn’t even write a program:

> python
Python 2.6 (r26:66714, Mar 17 2009, 11:44:14) 
[GCC 4.4.0 20090313 (Red Hat 4.4.0-0.26)] on linux2
Type "help", "copyright", "credits" or "license" for more information.
>>> import ephem
>>> t = ephem.Date('2011/05/06')
>>> s = ephem.Date('2011/06/21')
>>> print ephem.Date(s+(s-t)*ephem.hour*24)
2011/08/06 00:00:00

In other words: the alternative “Pixar-Henge” day is August 6.

But what angle is our hallway aligned? For that., I fired up Google Earth, and used their measurement tools. Assuming that the long hallway runs parallel to the long side of the building, I determined that the length of our building was approximately 140 meters, and was at an angle of 75.22 degrees.

But here is the thing: I then did the calculation on pyephem to see what direction it thought the rising sun would be: and it came up with 68 degrees. That just seems wrong. Not sure what to think here. I’ll ponder it some more.