Today on my drive north to the path of the November 14 total eclipse in Australia, I crossed the Tropic of Capricorn and am now officially in the tropics.

This is one of the many monuments that the demarcates this important line around the world, all located at 23.5° south latitude (or thereabouts). This one is in Rockhampton, Queensland. It’s actually at 23° 23′ 59″ S but that’s close enough for tourists. For photos of other Tropic of Capricorn monuments see Wikipedia’s page.

The Tropic of Capricorn is one of the world’s four main lines of latitude defined by the tilt of the Earth: The Arctic and Antarctic Circles at 66.5° N and S, and the Tropics of Cancer and Capricorn, at 23.5° N and S. The names for the Tropic lines come from the two constellations where the Sun used to be located millennia ago on the June and December solstices: Cancer and Capricornus. The precession motion of the Earth’s axis has since moved the Sun into Gemini and Sagittarius on those key annual dates.

The Tropic of Capricorn is the southernmost latitude on our planet where the Sun can appear directly overhead at the zenith, and then only on one day, the December solstice. I was here close to that date a few years ago and can attest to the lack of shadows at “high noon” at solstice on a Tropic line.

The zone on Earth between the two Tropic lines, between 23.5° N and 23.5° S, is of course called the Tropics. While the Sun may not always be overhead in the tropics it certainly is always high at mid-day. And hot!

Next stop: Magnetic Island, named by James Cook in 1770 as he thought the island was affecting his compass in strange ways.

– Alan, November 6, 2012 / © 2012 Alan Dyer