The imaginary lines of the Earth are geographical references that do not physically exist, but that allow us to orient ourselves and locate any point on the planet. They are represented on maps and planispheres, forming a grid that extends from north to south and from east to west. These lines are divided into meridians and parallels, and are central to cartography, navigation, and modern geography.
Thanks to meridians and parallels, it is possible to establish precise geographical coordinates, which are expressed by latitude and longitude. Its study allows us to understand natural phenomena such as the succession of day and night, the duration of the seasons and the incidence of solar radiation on different regions of the Earth.
Terrestrial meridians
Meridians are imaginary circles that cross the Earth from pole to pole, connecting the North Pole to the South Pole. Each meridian is complemented by its opposite, called the antimeridian, forming a complete circle around the planet.
Main characteristics of the meridians
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All points located on the same meridian experience noon at the same time, although the official time may vary due to time agreements.
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The total length of a meridian or antimeridian is approximately 20,004.5 km, considering the earth's surface.
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The Greenwich meridian, located in England, is the zero meridian and serves as an international reference. It divides the Earth into the Eastern Hemisphere and the Western Hemisphere.
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The Greenwich antimeridian mainly crosses the Pacific Ocean and marks the famous International Date Line, where the official date is adjusted when crossing from one temporal hemisphere to the other.
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Each point on Earth belongs to a single meridian, which defines its longitude, measured as the angle between the Greenwich meridian and the local meridian.
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Longitude is measured from 0° to 180° to the east (E) or to the west (W).
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Practical example:
If a place is 75°W of Greenwich, it means that it is 75 degrees west of the reference meridian. This is critical for maritime and air navigation, as well as global positioning systems (GPS).
Terrestrial parallels
Parallels are imaginary lines that form circles around the Earth, perpendicular to its axis of rotation. Unlike meridians, they do not pass through the poles and are parallel to each other, hence their name.
The equator: the fundamental parallel
The equator is the most important parallel and divides the Earth into the northern hemisphere and the southern hemisphere. It is the only parallel whose plane is perpendicular to the Earth's axis, and above it the Earth has its maximum circumference, approximately 40,075 km.
- The Sun's rays fall perpendicularly on the equator during the equinoxes, marking days and nights of equal length.
- All other parallels are minor circles that decrease in length as they move away from the equator toward the poles.
Other notable parallels
- Tropic of Cancer (23.5°N) and Tropic of Capricorn (23.5°S): The Sun's rays fall perpendicularly on these parallels during the June and December solstices, respectively.
- Arctic Circle (66.5°N) and Antarctic Circle (66.5°S): delimit the regions where phenomena such as the midnight sun and the polar night occur.
Latitude: the measurement associated with the parallels
Latitude indicates the angular distance of a point from the equator.
- It is measured from 0° at the equator to 90° at the poles, with the indications North (N) or South (S) as appropriate.
- Thanks to latitude and longitude, any place on Earth can be located precisely.
Practical example:
The city of Quito, in Ecuador, is very close to the equator (approximately 0°S), while New York is at 40°42′N. This information helps determine the climate, the length of the days, and the intensity of solar radiation.
Relationship between imaginary lines and solar radiation
Meridians and parallels not only serve to orient oneself, but also help to understand how solar radiation falls on the Earth, which influences the climate, the seasons and the distribution of sunlight throughout the day and the year.
Parallels and radiation intensity
Latitude, measured from parallels, determines the angle of incidence of the sun's rays.
At the equator, the Sun's rays fall almost perpendicular to the surface, resulting in higher temperatures throughout the year.
As we approach the poles, the rays arrive more inclined, distributing the solar energy over a larger surface area and causing a colder climate.
The tropics (Cancer and Capricorn) mark the boundaries where the Sun's rays fall directly on the surface during the solstices, which explains the existence of areas with high temperatures and dry or wet seasons in the tropics.
Polar circles define regions where, at least one day a year, the Sun does not set or rise, a phenomenon known as the midnight sun or polar night, directly affecting the amount of solar radiation received.
Meridians and the time distribution of sunlight
The position of the meridians determines the time of day when the Sun reaches its highest point, that is, local noon.
Thanks to the meridians, time zones can be defined, which allows you to coordinate the solar time with the official time of each region.
This is important for photovoltaic and thermal solar energy, since energy production depends on the solar radiation available at each place and time of the day.
Conclusion
Meridians and parallels are essential tools for understanding geography, navigation, and natural phenomena that depend on the Earth's position relative to the Sun. Although they are imaginary lines, their usefulness is concrete and daily: from calculating the exact time to defining climatic zones, including the location of any point on our planet.