Wednesday, 24 December 2014

Circles Circles Everywhere

Undoubtedly you have gazed upon a globe at some-point within you lifetime. Whether this be in a school class, a university lecture theater or before deciding where in the world you wish to visit on your next adventure overseas. In most cases, you will recognise the shapes of some of the countries and oceans, and maybe even acclaim a few facts or points of interest. But how many times have you looked at the lines that horizontally circle the globe, such as the Tropic of Capricorn or the Tropic of Cancer, and questioned exactly what these lines mean. If somebody were to ask you now, what does the Tropic of Capricorn represent, would you be able to answer? If so, then I congratulate you. However, most would not, and it is to this majority that this article is aimed.

So without further ado, let's begin.

The Circles of Latitude described in the most simple of terms, are the lines that horizontally circle the earth. There are five major circles of latitude, which when defined from north to south, are as follows:

1. Arctic Circle
2. Tropic of Cancer
3. Equator
4. Tropic of Capricorn
5. Antarctic Circle

The aim of these circles is to separate the earth into five geographical zones, known as the following:

1. The North Frigid Zone (north of the Arctic Circle)
2. The North Temperate Zone (between the Arctic Circle and the Tropic of Cancer)
3. The Torrid Zone (between the Tropical Circles)
4. The South Temperate Zone (between the Tropic of Capricorn and the Antarctic Circle)
5. The South Frigid Zone (south of the Antarctic Circle)

As is clearly evident, the zones stated above are separated due to their prospective conditions of climate. This enables us to study the planet with additional precision, with regards to the climate and its effect on earth. Studies have found that each of these zones host a startling variety of biodiversity, all of which is entirely dependent upon that zone's climate conditions. This is one of many influencing factors as to why certain species of plants and animals are only found in certain areas. However, it is all well and good understanding what the five major lines of latitude represent, but this knowledge poses an additional question. How are the lines of latitude measured? In other words, how did we calculate where the lines belonged in the first place?

For the sake of simplicity, we shall follow the pattern stipulated above and investigate each of the lines of latitude from north to south.

1. Arctic Circle:

The Arctic circle represents the southern most point in the northern hemisphere where the sun can remain either above or below the horizon for a full 24 hour period. Effectively, anywhere above this line will experience either perpetual day or perpetual night, each year, dependent upon the season. In addition, due to the effects of the tide and moon the Arctic Circle is currently drifting north at a rate of roughly 15 meters per year.

2. Tropic of Cancer

The Tropic of Cancer represents the northern most point at which the sun can be seen directly overhead during the June solstice. This line, like each of the others in not permanently fixed in position, and has been calculated to drift south very slowly year on year.

3. Equator

The Equator represents the point on earth that is equidistant from both the north and south poles. Any point above the Equator is within the northern hemisphere; and anywhere below the Equator is within the southern hemisphere. Of all the lines of latitude, the Equator is the longest at 24,902 miles. Additionally, the earth rotates at roughly 1,000 miles per hour, therefore, taking approximately 24 hours to undertake an entire rotation. Hence the length of a day. However, the earth's rotation speed reduces the further you travel from the equator due to a reduction in circumference. Consequently, the further you live from the equator, the slower you are travelling.

4. Tropic of Capricorn

The Tropic of Capricorn is the literal opposite of the Tropic of Cancer. The Tropic of Capricorn represents the southern most point on earth at which the sun can be seen directly overhead during the December solstice. This line has been monitored and is calculated to be moving north at a rate of 15 meters per year.

5. Antarctic Circle

The Antarctic Circle represents the northern most latitude contained within the southern hemisphere where the sun can remain either above or below the horizon for a full 24 hour period. At present the Antarctic Circle covers an area of roughly 7,700,000 sq miles (4% of the earth's surface), but is drifting further south each year.

As can be seen from above, the earth contains a variety of geographical zones, each integral to our climate and well-being. However, with the Tropic of Cancer drifting south and the Tropic of Capricorn drifting north, the gap between the two is reducing year on year as they both slowly encroach upon the Equator. Additionally, as the Arctic Circle drifts further north and the Antarctic Circle slides further south, the areas that we consider to be the poles of earth are also shrinking. This, however, is an entirely natural occurrence and is due to slight alterations within the earth's plane of orbit around the sun, and its fluctuation of axis.

A series of photographs taken at 2 hour intervals, which show a full 24 hours of perpetual day in Antarctica. It can clearly be seen that at no point does the sun drop below the horizon.  

A basic depiction of each of the earth's lines of latitude.

A representation of earth's tilt.

- Until the next Butterfly...