Starry Night sounds awesome. Maybe I'll get it someday. (Like in 2013?)
Thanks for putting real numbers on how much effect the change in the Earth's tilt would have. Jenkins mentions that the tilt has changed since 2100 BCE, but (like Aveni) concludes that to a naked-eye observer, that change wouldn't make much difference. I thought I'd let it go at that, since the point of the video is that Jenkins himself is documenting that there's never been anything "unique" about the Solstice Day sunrise at the Group F ballcourt.
The hills in the background do make a difference. Atmospheric refraction counteracts the effect of hills, but the Sky Charts azimuths I give seem to account for refraction. (I.e., the azimuths calculated by Skycharts varied with atmospheric pressure, and in the right direction.) The bottom line is that the Sunrise azimuths I presented should be correct for a horizon without hills, in a lowland area like Izapa. I considered getting a topo map of Izapa so I could look into the effect of the hills, but as Aveni describes in Skywatchers, it would be a fair amount of work, and I was afraid I'd just lose the viewers in the details.
I still might do it sometime, because it's a problem that might interest students here. And since I live only a day's travel from Izapa, I might even go there someday. But I expect that at dawn on Winter Solstice day, the place will be a zoo.
(account deleted) 08 Dec 2010 02:23