The position of the Tropic of Capricorn is not stable, but moves continually due to a minor wobble in the Earth's longitudinal alignment relative to its orbit around the Sun. Over a 41,000-year period, the Earth's axial tilt changes between 22.1 to 24.5 degrees, with the present value being around 23.4 degrees. This means that there are about 6,900 hours of daylight during each year and that the seasons are reversed compared to what we are used to.
The tropics are areas of high atmospheric pressure which cause temperatures to be high enough for water to remain in the liquid state even at low elevations. The Tropic of Capricorn is located in the center of the African continent near the city of Dar es Salaam. It is the only tropical zone on land and extends from 16 degrees North to 14 degrees South latitude.
The average temperature inside the tropics is higher than 10 degrees Celsius (50 degrees Fahrenheit) all year round. Rainfall is heavy around the clock, except when clouds block out the sun. During these periods of darkness, so-called "twilight" temperatures can reach levels very close to zero degrees Celsius (32 degrees F).
Outside the tropics, the average temperature drops below 10 degrees Celsius (50 degrees F) only during winter months. Daytime temperatures rarely drop below 0 degrees Celsius (32 degrees F) and can rise as high as 40 degrees Celsius (100 degrees F).
The axial tilt of the Earth is responsible for the Tropics of Cancer and Capricorn being located at around 23.5 degrees north and south, respectively. Every year, the Earth is tilted 23.5 degrees off the plane of the Earth's revolution around the sun. The tropics, on the other hand, may be frigid. For example, New York City has a tropical climate, but only because it is so close to the equator that the effect of the Earth's rotation is still felt there. If you were to walk out on the sidewalk in Manhattan and start walking west, you would soon find yourself in the rain.
The axis of the Earth's rotation is also called the polar axis. It is almost always pointed straight up or straight down, except during major earthquakes when it can swing back and forth. The equatorial plane is the horizontal surface shared by all points on the globe that are equal distance from the center of the earth. Since the Earth is spinning, objects near the equator experience less force from gravity than those same objects would if the Earth weren't spinning. As a result, planets orbit the Sun more closely than they would if the Earth wasn't spinning.
The two tropics are separated by a point called the equator. The equator is the line connecting Earth's North and South Poles. It is the only place on Earth where east and west meet at right angles (90 degrees).
The Tropic of Capricorn goes across Australia, Chile, southern Brazil (the only nation that travels through both the equator and a tropic), and northern South Africa. This is one of the two tropical zones on Earth, the other being the Arctic Circle.
These areas share the same astronomical features: The sun rises every morning over the equator, reaches its highest point around noon, and begins its descent toward the west after nightfall. At the same time, it sets every evening over the pole, where it will rise again the next day.
The reason these regions form a tropical zone is because they are within the tropics of the earth's globe. The tropics are any region of the world where the sun appears to rise and set over a single location during the course of a year. They are defined by the latitude of 23 degrees N or S, but since the axis of the planet rotates about its center, each hemisphere has three pairs of parallel bands of constant sunrise and sunset times: One pair lies near the equator, another near the poles.
At these locations, the sun is directly over the equator or the north pole at mid-summer and directly below the equator or the south pole at mid-winter.
The Tropic of Capricorn separates the Southern Temperate Zone to the south from the tropics to the north. The Tropic of Cancer is the Northern Hemisphere's equivalent of the Tropic of Capricorn. At 23deg26'11.7"S, the length of the Tropic of Capricorn is 36,788 kilometers (22,859 mi).
The axis about which a planet or moon orbits is called its "axis of rotation". Earth has two such axes: one that passes through its center and ends in each of its feet; another that lies almost perpendicular to the first axis and passes through the center of Earth's surface. These are called the "tropical" and "polar" axes, respectively.
The point on either of these axes that is closest to Earth's center is called its "equatorial bulge". This is because it resembles a bulge in the surface of a sphere. The reason for this is that the equator is where all the world's land masses are located, so they exert a large influence over Earth's shape.
The line connecting a body's equatorial bulge with its center of mass is called its "orbit". All the planets except Mercury have orbits around Earth's biconcave mollusk-shaped body. Mercury has an extremely elliptical orbit, so it travels far away from then toward Earth before looping back again.