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Latitude

Latitude indicates the location of a place on Earth north or south of the Equator. Latitude is an angular measurement in degrees (marked with °) ranging from 0° at the Equator to 90° at the poles (90° N for the North Pole or 90° S for the South Pole).


Degrees of latitude are parallel so the distance between each degree remains almost constant. Each degree of latitude is approximately 69 miles (111 kilometers) apart. The distance varies (due to the earth's slightly ellipsoid shape) from 68.703 miles (110.567 km) at the equator to 69.407 (111.699 km) at the poles. This is convenient because each minute of latitude (1/60th of a degree) is approximately one mile.




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45th Parallel


Important named circles of latitude


There are five circles of latitude that are named because of the role they play in the geometrical relationship with the Earth and the Sun:



Each of the five main latitude regions of the earth's surface marks the boundary between the so called geographical zones. The differences between them relate to climate, and the behaviors of the sun.


The Tropics

The tropics are the geographic region of the Earth centered on the equator and limited in latitude by the Tropic of Cancer in the northern hemisphere, at approximately 23° 26' (23.5°) N latitude, and the Tropic of Capricorn in the southern hemisphere at 23° 26' (23.5°) S. This area includes all the parts of the Earth where the sun reaches a point directly overhead at least once during the solar year.


Tropical plants and animals are those species native to the tropics. Tropical is also sometimes used in a general sense for a tropical climate, a climate that is warm to hot and moist year-round, often with the sense of lush vegetation. However, there are places in the tropics that are anything but "tropical" in this sense, with even alpine tundra and snow-capped peaks, including Mauna Kea, Mt. Kilimanjaro, and the Andes as far south as the northernmost parts of Chile and Argentina. Places in the tropics which are drier with low humidity but extreme heat are the Sahara Desert, Central Africa, and Northern Australian Outback.



The temperate zone

The north temperate zone extends from the Tropic of Cancer at about 23.5 degrees north latitude to the Arctic Circle at about 66.5 degrees north latitude. The south temperate zone extends from the Tropic of Capricorn at about 23.5 degrees south latitude to the Antarctic Circle at about 66.5 degrees south latitude. These regions experience four seasons, spring, summer, autumn and winter. Within these borders there are many individual climate types, which are generally grouped into two categories; continental and maritime, or Oceanic climate.


The difference in these regions between summer and winter are generally subtle, warm or cool (relatively speaking), rather than extreme, burning hot or freezing cold. However, a temperate climate can have very unpredictable weather and violent storms especially in spring and summer. The weather pattern can change rapidly; one day it may be sunny, the next it may be raining, and after that it may be cloudy. These erratic weather patterns occur in summer as well as winter.


Polar climate

There are two distinct types of polar climate. The tundra climate is the less severe of the two, and there is at least one month that has an average temperature of above freezing. The second type of polar climate is known by various names including the "ice cap climate" and the "perpetual frost climate" and features sub-freezing average temperatures year-round.





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The Tilted Earth


The planet Earth has an axial tilt of about 23° 27´ in relation to the sun. The northern end of the Earth's axis always points to the same place in space (towards the star called Polaris or the North Star). Because the axis is tilted in the same direction all year as the Earth orbits the Sun, the number of hours of daylight and the angle at which the sun light strikes the earth changes. This is what causes the seasons in the temperate zones. The hemisphere (half part of earth) tilted away from the Sun experiences winter while the hemisphere tilted towards the Sun will experience summer (see effect of sun angle on climate). The hemisphere that is currently tilted toward the Sun experiences more hours of sunlight each day, and the sunlight at midday also strikes the ground at an angle nearer the vertical and thus delivers more heat.


From Wikipedia:


In astronomy, axial tilt is the inclination angle of a planet's rotational axis in relation to a perpendicular to its orbital plane. It is also called axial inclination or obliquity. The axial tilt is expressed as the angle made by the planet's axis and a line drawn through the planet's center perpendicular to the orbital plane.


The sun "travels " between the Tropic of Cancer (23.5 N) on the Northern Solstice (first day of summer in the Northern Hemisphere) to the Tropic of Capricorn (23.5 S) on the Southern Solstice and back to the Tropic of Cancer in one year (365 days). Thus the sun travels 47 degrees of latitude * 2 (to compensate for the round trip) = 94 degrees of latitude during a solar year. It is a simple calculation to compute the average daily movement of the sun (94 degrees/365 days = ~.258 degrees/day or ~15.5 nautical miles/day.


Axis Tilt and Solar Altitude

The annual change in the relative position of the Earth´s axis in relationship to the sun causes the height of the sun (solar elevation angle) to vary in our skies. The difference in maximum solar altitude for any location on the Earth over a one year period is 47° (2 x 23.5° = 47°). For example, at 34° N maximum height of the sun varies from 79.6° on the summer solstice to 32.6° N on the winter solstice.



Seasons
Temperate
Spring
Summer
Autumn
Winter
Tropical
Dry
season
Cool season
Hot season
Wet season
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Arctic Circle: 66° 33' 39" N



The Arctic Circle is the parallel of latitude that runs 66° 33´ 39" (or 66.56083°) north of the Equator and is one of the five major circles of latitude that mark maps of the Earth. Everything north of this circle is known as the Arctic, and the zone just to the south of this circle is the Northern Temperate Zone. The Arctic consists of ocean surrounded by continental land masses and islands. The central Arctic Ocean is ice-covered year-round, and snow and ice are present on land for most of the year.


The Arctic Circle marks the southern extremity where the sun is above the horizon for 24 continuous hours at least one day per year in June on the northern (or summer) solstice), and where the sun will be below the horizon for at least 24 continuous hours in December (winter or Southern solstice). The position of the Arctic Circle is determined by the axial tilt (angle) of the polar axis of rotation of the Earth on the ecliptic. This angle is not constant, but has a complex motion determined by many cycles of short to very long periods.


The summer or northern solstice occurs in June when the sun is directly over the Tropic of Cancer. This is the day when people in the Northern Hemisphere experience the longest period of day light and is the first day of summer. At this same time it is the first day of winter in the Southern Hemisphere.


Countries which have significant territory within the Arctic Circle are:


  • Canada
  • Denmark (Greenland)
  • Finland
  • Norway
  • Russia
  • Sweden
  • United States (Alaska)
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Tropic of Cancer: 23° 26' 22" N


The Tropic of Cancer is the parallel of latitude that runs 23° 26' 22" north of the Equator and is one of the five major circles of latitude that mark maps of the Earth.


The Tropic of Cancer is the farthest northern latitude at which the sun can appear directly overhead. The sun is directly over the Tropic of Cancer at noon on the summer or northern solstice. North of this line is the subtropics and Northern Temperate Zone. The Solstice occurs in June of each year and is the day when people in the Northern Hemisphere experience the longest period of day light and is the first day of summer. At this same time it is the first day of winter in the Southern Hemisphere.


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Equator: 0° 0' 0"



The Equator is an imaginary circle drawn around a planet (or other astronomical object) at a distance halfway between the poles. By definition, the equator is latitude 0° 0' 0" and is one of the five major circles of latitude that mark maps of the Earth.


An equinox in astronomy is the event when the Sun can be observed to be directly above the Earth's equator. The event occurs twice a year, around March 20 and September 23 and marks the first day of spring or autumn. More technically, the equinox happens when the Sun is at one of two opposite points on the celestial sphere where the celestial equator and ecliptic intersect. In a wider sense, the equinoxes are the two days each year when the Sun spends an equal amount of time above and below the horizon at every location on Earth (equal night and day).


The equator passes through 13 countries:
  • Ecuador
  • Colombia
  • Brazil
  • Sao Tome & Principe
  • Gabon
  • Republic of the Congo
  • Democratic Republic of the Congo
  • Uganda
  • Kenya
  • Somalia
  • Maldives
  • Indonesia
  • Kiribati

Circumference of the Earth

The circumference of the earth at the equator is 24,901.55 miles (40,075.16 kilometers). But, if you measure the earth through the poles the circumference is a bit shorter - 24,859.82 miles (40,008 km). Thus the earth is a tad wider than it is tall, giving it a slight bulge at the equator. This shape is known as an ellipsoid or more properly, geoid (earth-like).


Eratosthenes, a Greek scholar and Mathematician, determined the circumference of the Earth in 240 BC, using trigonometry and knowledge of the angle of elevation of the Sun at noon in Alexandria and in the Elephantine Island near Syene (now Aswan, Egypt). Eratosthenes knew that on the summer solstice at local noon in the town of Syene on the Tropic of Cancer, the sun would appear at the zenith, directly overhead. Eratosthenes needed two things, the angle of the Sun in Alexandria and the distance from Alexandria to Syene. He knew that the approximate distance between Syene and Alexandria, as measured by camel-powered trade caravans was 5000 stadia (800 km or 497.10 miles). He also knew, from measurement, that in his hometown of Alexandria, the angle of elevation of the Sun would be 7.2° south of the zenith at the same time. By taking the angle of the shadow (7°12´) and dividing it into the 360 degrees of a circle (360 divided by 7.2 yields 50), Eratosthenes could then multiply the distance between Alexandria and Syene by 50 to determine the circumference. Eratosthenes determined the circumference to be 25,000 miles, just 100 miles over the actual circumference at the equator (24,901 miles).


Earths equatorial bulge

An equatorial bulge is a planetological term which describes a bulge which a planet may have around its equator, distorting it into an oblate spheroid. The Earth has an equatorial bulge of 26.5 miles (42.72 km) due to its rotation.


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Tropic of Capricorn: 23° 26' 22" S



The Tropic of Capricorn is the parallel of latitude that runs 23° 26' 22" south of the Equator and is one of the five major circles of latitude that mark maps of the Earth.


The Tropic of Capricorn is the farthest southern latitude at which the sun can appear directly overhead. The sun is directly over the Tropic of Capricorn at noon on the winter or southern solstice. South of this line is the subtropics and Southern Temperate Zone. The Solstice occurs in December of each year and is the day when people in the Southern Hemisphere experience the longest period of day light and is the first day of summer. At this same time it is the first day of winter in the Northern Hemisphere.


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Antarctic Circle: 66° 33' 39" S



The Antarctic Circle is the parallel of latitude that runs 66° 33´ 39" (or 66.56083°) south of the Equator and is one of the five major circles of latitude that mark maps of the Earth. The continent south of this circle is Antarctica, and the zone just to the north of this circle is the Southern Temperate Zone. Antarctica is surrounded by the southern waters of the World Ocean. At 14.4 million km², Antarctica is the fifth-largest continent in area.


The Antarctic Circle marks the northern extremity where the sun is above the horizon for 24 continuous hours at least one day per year in December on the southern (or winter) solstice), and where the sun will be below the horizon for at least 24 continuous hours in June (summer or northern solstice). The position of the Antarctic Circle is determined by the axial tilt (angle) of the polar axis of rotation of the Earth on the ecliptic. This angle is not constant, but has a complex motion determined by many cycles of short to very long periods.


The winter, or southern, solstice occurs in December when the sun is directly over the Tropic of Capricorn and is the day when people in the Southern Hemisphere experience the longest period of day light. This is the first day of summer in the Southern Hemisphere. At this time it is the first day of winter in the Northern Hemisphere.


The Antarctic Treaty was signed in 1959 by 12 countries. The treaty prohibits military activities and mineral mining, supports scientific research, and protects the continent's ecozone. Ongoing experiments are conducted by more than 4,000 scientists of many nationalities and with different research interests.


The original signatories of the Antarctic Treaty are:


  • Argentina
  • Australia
  • Belgium
  • Chile
  • France
  • Japan
  • New Zealand
  • Norway
  • South Africa
  • USSR
  • United Kingdom
  • United States
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Determining Latitude



The easiest method to determine your latitude in the Northern Hemisphere is to determine how many degrees above the horizon Polaris (or the North Star) is (see A simple method for determining your Latitude ). This method will not work during the day, in the Southern Hemisphere or when it is cloudy at night.


Before the development of modern navigational aids, mariners used an Astrolabe to determine the latitude of the ship at sea. The noon altitude of the Sun was measured during the day or the altitude of a star of known declination was measured when it was on the meridian (due north or south) at night. The Sun's or star's declination for the date was looked up in an almanac. The latitude is then 90° - measured altitude + declination. The Astrolabe was later replaced by the Sextant.



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A simple method for determining your Latitude (North of the Equator)


You can determine you latitude by finding the angle between your location and the North Star (Polaris) by contracting your own simple Mariner's Astrolabe. If you do not know how to find the North Star, check out the sites listed in this section. You can build your own astrolabe using the following instructions or by using the information contained on any of the web sites listed below.



Make a Simple Mariner's Astrolabe

Astrolabe

You will need the following supplies:

  • Thread or light string
  • protractor
  • a weight (paper clip or washer)
  • tape
  • Long straw or paper rolled into a ¼-inch tube
  • small notebook and pencil
  • small flashlight or "penlight"

Instructions:
  1. Tie a thread around the middle of the straight side of the protractor leaving about an 8-inch length (if your protractor has a hole in the middle use that).
  2. Tie the paper clip or washer to the long end of the thread. When you hold the protractor level to the ground, the thread should cross the protractor at the 90° mark.
  3. Tape the flat edge of the protractor to the length of the straw.
  4. Go outside at night when there are lots of stars out.
  5. Identify the North Star (see list of web sites on how to find the North Star below).
  6. Look at the North Star through your straw, making sure the thread with the paperclip weight is hanging free.
  7. Hold the thread in place against the protractor after you locate the North Star.
  8. Take it down from your eye and read the degrees on the protractor where the thread crosses the protractor (Read the inner set of numbers, from 0 to 90 degrees.) This number is the zenith angle. To find the altitude angle, subtract the zenith angle from 90°. This number will be the same as, or very close to, your latitude.
  9. Write down this number in your notebook.
  10. Take this reading several more times, noting the degrees in your notebook each time, to check for accuracy.
  11. There are several web sites that will tell you your latitude (some are listed below) or use an atlas or a map.


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More information about latitude




   For more information about latitude, visit the following sites:



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