Welcome to Gaia! ::

Pretty basic stuff.
Most of us have known something about this since grade school. What fascinates me about it is how we figured it out in the first place, especially before the advent of satellites and space travel. I haven't studied astronomy enough to understand fully how we came to know this. The axis is, after all, an imaginary line. But here's an eloquent perspective on that question

Interested in more about the science and math? Tough, I'm finished with that. On to Geography!

When it's winter solstice in the Northern Hemisphere, the sun is directly overhead at noon only along the Tropic of Capricorn, on which lie such places as Sao Paulo, Brazil, southern Madagascar, and areas north of Brisbane, Australia.

It's a charming theory. But who knows how accurate it is? Cultural anthropology has advanced a lot in the last 50 years.

Many, many cultures the world over perform solstice ceremonies. At their root: an ancient fear that the failing light would never return unless humans intervened with anxious vigil or antic celebration.

Scholars haven't yet found proof that these peoples had the skill to pinpoint a celestial event like solstice. Earliest markers of time that we've found from these ancient peoples are notches carved into bone that appear to count the cycles of the moon. But perhaps they watched the movement of the sun as well as the moon, and perhaps they celebrated it -- with fertility rites, with fire festivals, with offerings and prayers to their gods and goddesses.

The ancients: huge efforts to observe the solstices

An utterly astounding array of ancient cultures built their greatest architectures -- tombs, temples, cairns and sacred observatories -- so that they aligned with the solstices and equinoxes. Many of us know that Stonehenge is a perfect marker of both solstices.

The light illuminates a stone basin below intricate carvings -- spirals, eye shapes, solar discs. Although not much is known about how Newgrange was used by its builders, marking the solstice was obviously of tremendous spiritual import to them. Here's more on this incredible ancient site.

Hundreds of other megalithic structures throughout Europe are oriented to the solstices and the equinoxes. The blossoming field of archaeoastronomy studies such sacred sites in the Americas, Asia, Indonesia, and the Middle East. Recent research into the medieval Great Zimbabwe in sub-Saharan Africa (also known as the "African Stonehenge") indicates a similar purpose. In North America, one of the most famous such sites is the Sun Dagger of Chaco Canyon, New Mexico, built a thousand years ago by the Chacoans, ancestors of the Pueblo people. Even cultures that followed a moon-based calendar seemed also to understand the importance of these sun-facing seasonal turning points.