# Latitudes and Longitudes

## What are Latitudes and Longitudes?

Latitudes and longitudes are fictional lines employed to ascertain the position of a location on Earth. As the Earth has a “Geoid” shape, we utilize latitudes and longitudes for navigation and mapping purposes. For instance, the coordinates for Agra are 27° 10′ 3.792” N, 78° 2′ 9.204” E, while New Delhi is located at 28° N, 77° E.

## History and development

The concept of latitude and longitude has been around for centuries. The ancient Greeks were among the first to use a primitive form of latitude in navigation. However, the modern system we use today was developed much later, with significant contributions from figures like Hipparchus, Ptolemy, and later, John Harrison, who invented the marine chronometer – a critical tool for accurate longitude measurement at sea.

## The Degree System

Both latitude and longitude are measured in degrees (°), minutes (‘), and seconds (“). There are 60 minutes in a degree and 60 seconds in a minute. This system allows for precise measurements.

• Latitude Degrees: The Earth is divided into 180 equal parts both north and south of the Equator, totaling 360°. Each degree of latitude is approximately 69 miles (111 kilometers) apart.
• Longitude Degrees: The Earth is also divided into 360 degrees of longitude, but unlike latitude, these vary in size. At the Equator, one degree of longitude is approximately the same as one degree of latitude (69 miles), but this distance decreases as you move towards the poles.

## The Latitudes

Latitudes are the angular distance of a point on the earth’s surface. It is measured in degrees from the centre of the earth. The earth is slightly flattened at the poles. Therefore, the linear distance of a degree of latitude at the pole is a little longer than that at the equator, due to the bulge at the equator.

For example, at the equator (0°) it is 68.704 miles. At 45° it is 69.054 miles. At the poles, it is 69.407 miles. 69 miles (111km). (1 mile = 1.607 km) is the average distance.

### Important Latitudes

In addition to the equator (0°), the North Pole (90°N), and the South Pole (90°S), there are four significant lines of latitude:

1) Tropic of Cancer (23½° N) in the northern hemisphere.

2) Tropic of Capricorn (23½° S) in the southern hemisphere.

3) Arctic circle at 66½° north of the equator.

4) Antarctic circle at 66½° south of the equator

### Latitudes and Heat Zones

There are 3 heat zone regions on Earth. These zones lie between the important latitudes we discussed above- The Torrid, Temperate and Frigid zone.

The mid-day sun is directly above the head at least once a year on all latitudes between the Tropic of Cancer and the Tropic of Capricorn. This region, as a result, experiences the highest amount of heat and is known as the torrid zone.

The mid-day sun never shines overhead on any latitude beyond the Tropic of Cancer and the Tropic of Capricorn. The angle of the sun’s rays gradually decreases as you move towards the poles. These areas are bounded by the Tropic of Cancer and the Arctic Circle in the northern hemisphere and the Tropic of Capricorn and the Antarctic Circle in the southern hemisphere, have moderate temperatures. These are, therefore, called temperate zones.

The regions located between the Arctic Circle and the North Pole in the Northern Hemisphere, as well as the Antarctic Circle and the South Pole in the Southern Hemisphere, experience extremely cold temperatures. This is due to the limited elevation of the sun above the horizon in these areas. As a result, the sun’s rays always approach at a slanting angle. These regions are commonly referred to as the frigid zones. The 66.5° latitude line is drawn to mark the Arctic and Antarctic Circles. These circles are the northernmost and southernmost latitudes, respectively, at which the sun does not set at least once a year during the summer solstice, and does not rise at least once a year during the winter solstice.

What is Geodesy?

“Geodesy is the science of accurately measuring and understanding three fundamental properties of the Earth: its geometric shape, its orientation in space, and its gravity field— as well as the changes of these properties with time.”-oceanservice.noaa.gov

## The Longitudes

Longitudes are the angular distance, measured in degrees, that indicates the position of a location east or west of the Prime Meridian.

On the globe, longitudes are represented by a series of semi-circles that extend from the North Pole to the South Pole, passing through the equator. These lines are known as meridians

Unlike the equator, which is positioned at the centre between the poles, any meridian could have been chosen as the starting point for measuring longitude. In 1884, it was internationally agreed to designate the meridian that passes through the Royal Astronomical Observatory at Greenwich, near London, as the Prime Meridian (0°)

The Prime Meridian serves as the reference point from which all other meridians are measured, extending eastward and westward up to 180°.

As the parallels of latitude become shorter poleward, so the meridians of longitude, which converge at the poles, enclose a narrower space.

Meridians play a crucial role in determining local time in relation to Greenwich Mean Time (GMT), also known as World Time

### Longitudes and Time

Since the Earth completes a full rotation of 360° in one day or 24 hours, it covers 15° in one hour or 1° in 4 minutes

Due to the Earth’s eastward rotation, for every 15° travelled eastward, local time advances by 1 hour. Conversely, when travelling westward, local time is reduced by 1 hour.

Therefore, places east of Greenwich experience earlier sunrises and gain time, while places west of Greenwich witness later sunrises and lose time.

To determine local time based on Greenwich Mean Time, one simply needs to add or subtract the hour difference corresponding to the given longitude.

## Understanding Motions of the Earth through Latitudes and Longitudes

Latitudes and longitudes along with the motion of the earth help us understand different phenomena. Primarily earth moves in two ways Rotation and Revolution.

### Rotation

It takes approximately 24 hrs to complete one rotation.

Earth rotates along its axis from west to east.

Days and nights occur due to the rotation of the earth.

The circle that separates the illuminated part of the Earth from the dark part is known as the circle of illumination

The Earth’s axis of rotation is tilted. The angle between the Earth’s rotational axis and the normal (perpendicular) is 23.5°. This angle is also the angle between the Earth’s rotational axis and the orbital plane, which is the plane of the Earth’s orbit around the Sun.

### Revolution

The Revolution of the earth is responsible for the seasons we observe.

Earth moves around the sun in 365 days, 6 hours, and 9 minutes. All the usual years (non-leap years) are of 365 days and the remaining time (6 x 4= 24 hours) is added to a leap year. Therefore every fourth year, known as the leap year is of 366 days. An additional day is added to the month of February. February has 28 days in a non-leap year and 29 days in a leap year.

The northern hemisphere is tilted towards the sun on the 21st of June. The rays of the sun fall directly on the Tropic of Cancer. As a result, these areas receive more heat.

#### Effects of revolution

Areas near the poles receive less heat due to the slanting angle of the sun’s rays. Beyond the Arctic Circle, there is continuous daylight for approximately six months when the North Pole is tilted towards the sun.

In regions located north of the equator, it is summer because a significant part of the northern hemisphere is receiving sunlight. The longest day and shortest night in these areas occur on June 21st.

Conversely, in the southern hemisphere, the situation is reversed during this time. It is winter season there, with longer nights and shorter days. This position of the Earth is known as the summer solstice.

On December 22nd, the Tropic of Capricorn receives direct sunlight as the South Pole tilts towards it. Since the sun’s rays fall vertically at the Tropic of Capricorn (23.5° S), a larger portion of the southern hemisphere receives light. Therefore, it is summer in the southern hemisphere, with longer days and shorter nights. The opposite occurs in the northern hemisphere. This position of the Earth is called the winter solstice.

#### Equinox

On March 21st and September 23rd, the direct rays of the sun fall on the equator, resulting in a phenomenon known as the equinox. During the equinox, neither of the poles is tilted towards the sun, causing the entire Earth to experience equal days and equal nights.

On September 23rd, it is the autumn season in the northern hemisphere, which comes after summer and precedes winter. In the southern hemisphere, it is the spring season, occurring after winter and before the beginning of summer. The opposite is true on March 21st. During that time, it is spring in the northern hemisphere and autumn in the southern hemisphere.

Thus, you find that there are days and nights and changes in the seasons. This is because of the rotation and revolution of the earth respectively.

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