Tropic of Cancer

A novel by Henry Miller that deals with his sexual adventures, found controversial- primarily in America- for its challenging of sexual morality. All of Miller's works were banned from entering the U.S. in the early part of the 20th century, but in 1961 the ban was lifted.

Published in 1934, Tropic of Cancer is sort of an autobiographical piece of fiction, based on Miller's life as an expatriate American residing in Paris. A most excellent read, as well as the majority of his work.

Other works by Miller include "Tropic of Capricorn," "Sexus," "Plexus," and "Nexus," and numerous others. A prolific and unabashed writer, the stories of the love affair between him and Anais Nin is also an interesting read. A movie about said subject, "Henry and June," has gorgeous cinematography and is worth watching.

The Tropic of cancer is a parallel that circles around the Earth at a latitude of about 23°22'N. What makes this latitude special is that is the northernmost point on the globe where the Sun can stand directly overhead; this happens at the summer solstice, which is in June at the Northern Hemisphere. Hence, it marks the north boundary of the tropics.

On a globe, this tropic cuts through Mexico, passes under Florida, the Atlantic Ocean, cuts the Sahara almost in half, passes through the Middle East, India, goes through the south of China, and passes over the Pacific Ocean through Hawaii to arrive again in Mexico. If you were to make this tour, you'd encounter high temperatures, lush vegetation, desert, and, of course, oceans.

Okay, this is what most high school kids know of the Tropic of Cancer. But did you know it moves? Creeping around on the surface of the Earth, like a slug, only invisible and larger? You see, the point where the Sun is directly overhead of course depends on the tilt of the Earth's axis. This tilt varies from day to day, and means the location of the tropics moves by some meters per day, with all sorts of complicated patterns. This is caused by nutation, and is principally caused by the wobbling of the moon. There is also a long term tendency for the tilt to vary between 21.5° and 24.5°. This change takes place over a period of 41000 years, and currently, the average range of change is 0.5" per year. This corresponds to an average movement of this tropic by 15 meters per year, reducing the size of the Tropics by 1100 square kilometers per year, if the like movement of the Tropic of Capricorn is also taken into account.

To make matters worse, not only is the location not known, the name is also dead wrong. You might expect that the Tropic of Cancer is named after the constellation of Cancer, and you would be right. When it was named, the Sun was in the constellation of Cancer at the summer solstice. Nowadays, it is in the constellation of Taurus, due to precession of the Earth's axis.

In short, the Tropic of Cancer represents the north boundary of the Tropics. Its location is not fixed, but is around 23°22'.

See also: Tropic of Capricorn. Sources:

• http://en.wikipedia.org/wiki/Tropic_of_Cancer
• http://www.crystalinks.com/precession.html
• http://www.starlink.rl.ac.uk/star/docs/sun67.htx/node206.html
• http://www.pietro.org/Astro_Util_StaticDemo/MethodsNutationVisualized.htm