Summer Solstice 2005
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The image above shows the rising sun peeking out from behind the middle "V" of Four Peaks on the summer solstice seen from the bottom of the Mormon Trail in South Mountain Park, Phoenix, Arizona. The viewing area contains a boulder marked with a group of petroglyphs left by the Hohokam. Todd Bostwick refers to it as the Lizard Site in his book Landscape of the Spirits, no doubt named for the two most prominent figures found there (below right). I included the wide view, which shows some petroglyphs that have been painted over, to remind us that we need to protect these irreplaceable sites from mindless vandalism.

The Hohokam inhabited sites along the Salt and Gila rivers in and around the Phoenix area from about 300 to 1400 AD. Two of their sacred landmarks were the South Mountains located between the Salt and the Gila, and Four Peaks about 45 miles to the east. The Hohokam, like many other prehistoric people, would use the sun as a calendar to tell when to hold their seasonal ceremonies or to perform other important spiritual tasks. Sometimes the sun would be watched as it rose or set over a prominent landmark on the distant horizon. Another method was to use specially oriented petroglyph panels that interacted in meaningful ways with patterns of light and shadow falling across it. (Here's an example)

The Four Peaks sunrise is, of course, an example of a horizon calendar. For at least the last 2000 years, the summer solstice sun has risen from the central "V" of Four Peaks. This sunrise point has been slowly shifting southward (right) over time. When in use by the Hohokam, the sun rose more in the center, while in recent times, the first hint of light still shows in the "V", but the sun is actually just grazing that point. In a couple hundred years or so, the rising sun will pass right of the "V" and this prehistoric sunwatching site will no longer function.

Summer Solstice 101 - The Tilted Earth

The day of summer solstice is the longest of the year. It is also when the sun rises as far north as it can, attains its highest position in the noon sky, and then sets at its most northerly point. This all happens simply from the tilt of the Earth's axis. The graphics below help to illustrate this. The top one shows me standing in my backyard in Phoenix. I'm kind of short so I had to exaggerated my height a little in order to see me. I also shrank the sun to fit it in the picture.

The Earth's axis remains oriented towards the same point in space as we make the year-long journey around the sun. Currently, the north axis points very close to Polaris, the North Star. The yearly motion drastically changes our planet's tilt relative to the sun. When I go out in my yard and face south towards South Mountain at 12:30 PM (local noon) on the first day of summer, I am only about 10 degrees off from pointing directly at the sun. To me the sun appears nearly overhead and I am casting my shortest shadow possible from that location.
The globes were generated using:
Earth and Moon Viewer

Map features are from the Visible Earth Image by NASA
The illustration at left shows the Earth on the summer solstice just as above, but this time looking directly down onto the North Pole (red dot). It is noon for Phoenix and the 6:00 AM and 6:00 PM points show where Phoenix would be at those times. A line through the two 6:00 points defines a half-day period of 12 hours. The red arc shows the path Phoenix takes from sunrise to sunset as the Earth rotates counter-clockwise. It is easy to see the time spent in sunshine is greater than 12 hours. In fact, with the sun rising at 5:19 and setting at 7:41, the first day of summer in Phoenix is 14 hours 22 minutes in length. The longer time spent in sunlight, along with the directness of the rays, are the reasons why Phoenix is so hot in the summer—not that we are closer to the sun.

All images are copyrighted by Frank Zullo. Please do not use without written permission.