Understanding Latitude, Longitude, and Time Zones - Key Concepts on Earth's Coordinate System
Latitude, Longitude, and Time Zones - Key Concepts on Earth's Coordinate System
Day Light Saving (DST) & Earth
Daylight Saving Time (DST) involves advancing clocks by one hour during the summer months to make better use of natural daylight in the evening. This practice is particularly common in temperate regions, benefiting retail, sports, and reducing energy consumption by cutting down on evening lighting use. However, DST can also cause disruptions in timekeeping and other systems.
Earth is the only known planet where life exists.
Earth's surface is covered with two-thirds of water, making it a "blue planet."
It is the third planet from the Sun, the densest planet in the solar system, and the largest of the four terrestrial planets.
In size, Earth is the fifth-largest planet in the solar system.
Earth is slightly flattened at the poles, giving it a geoid shape, which means an earth-like shape.
Size and Shape of the Earth
The shape of Earth is described as a "geoid," meaning an Earth-like shape.
Earth is slightly flattened at the North and South Poles and bulges at the equator due to centrifugal force.
The shape of Earth is non-spherical because of the varying rates of movement at the equator and poles.
Motions of the Earth
The Earth has two primary motions: rotation and revolution. Earth's rotation is when it spins on its axis from west to east, taking approximately 24 hours to complete one full rotation, leading to day and night. Earth's revolution around the Sun takes 365¼ days, resulting in a leap year every four years.
Earth is constantly in motion, revolving around the Sun and rotating on its axis.
Rotation: Earth spins on its axis from West to East (counter-clockwise) and takes 23 hours, 56 minutes, and 4.09 seconds for a complete rotation, causing day and night.
Revolution: Earth revolves around the Sun in a counter-clockwise direction, taking one year to complete one revolution. The Earth's orbit is slightly oval, and the mean distance from the Sun is about 93 million miles.
The variation in the length of day and night from season to season is a result of the Earth’s rotation on its axis and its revolution around the Sun on a tilted orbit. This combination of motions causes changes in seasons and the varying durations of daylight and nighttime at different latitudes.
Leap Year
The revolution of the Earth refers to its orbit around the Sun, taking 365¼ days to complete. This motion causes seasonal changes. A leap year occurs every four years, when an extra day is added to February to account for the surplus time accumulated during the Earth's revolution.
Six hours saved every year are added to make one day (24 hours) over four years, resulting in a Leap Year with 366 days.
Earth Rotates in an Elliptical Orbit around the Sun
Earth rotates along its axis from west to east. This motion takes around 24 hours to complete, and it causes the alternation of day and night. The division between day and night on the globe is called the circle of illumination. Earth's axis is tilted at an angle of 23.5°, which influences the duration of day and night across the globe.
Earth's orbit around the Sun is elliptical, causing the distance between Earth and the Sun to change.
Perihelion: Earth is closest to the Sun around January 3.
Aphelion: Earth is farthest from the Sun around July 4.
Earth's axis points constantly to the same point (the polar star), causing the latitude at which the Sun’s rays fall vertically to change throughout the year.
Earth's Critical Positions
The equinox occurs twice a year, on 21st March and 23rd September, when the Sun's rays fall directly on the equator, resulting in equal lengths of day and night across the globe. During the equinox, the northern hemisphere experiences spring on 21st March and autumn on 23rd September, while the opposite occurs in the southern hemisphere.
Equinoxes: On MARCH 21 and SEPTEMBER 23, the Sun's rays are vertical at the equator, resulting in equal day and night worldwide.
On 21st June, the northern hemisphere is tilted towards the Sun, leading to summer and the longest day of the year. In contrast, the southern hemisphere experiences winter with shorter days. On 22nd December, the Sun's rays are directly on the Tropic of Capricorn, leading to summer in the southern hemisphere and winter in the northern hemisphere.
Summer Solstice: On June 21, the Sun's rays are vertical over the Tropic of Cancer, resulting in longer days in the NORTHERN HEMISPHERE.
Winter Solstice: On December 22, the Sun's rays are vertical over the Tropic of Capricorn, resulting in longer nights in the NORTHERN HEMISPHERE.
Why Days Are Longer than Nights at the Equator
Due to Earth's atmosphere, the sun’s rays are refracted, causing the apparent sunrise and sunset times to shift. This bending of light is stronger at sunrise and sunset, making days longer than nights at the equator, even though actual sunrises and sunsets would be more equal if there were no atmosphere.
Temperature and Latitude
Temperature falls with increasing latitude due to the Earth's spherical shape. The equator receives more direct sunlight compared to the poles, where sunlight is more diffused and less intense. The energy received per unit area decreases as one moves from the equator toward the poles.
Latitudes and Longitudes
Latitude and Longitude are imaginary lines used to determine the location of a place on Earth. The shape of the Earth is called a geoid. A location can be described using both latitude and longitude.
Example: The location of New Delhi is 28° N, 77° E.
Latitude is the angular distance of a point on Earth’s surface, measured in degrees from the center of the Earth.
As the Earth is slightly flattened at the poles, the linear distance of a degree of latitude at the poles is longer than at the equator. For example:
At the Equator (0°), the distance is 68.704 miles (111 km).
At 45°, the distance is 69.054 miles (111 km).
At the poles, the distance is 69.407 miles (111 km).
The average distance per degree of latitude is 69 miles (111 km), and 1 mile = 1.607 km.
Important Parallels of Latitude
Besides the Equator (0°), the North Pole (90° N) and the South Pole (90° S), there are four important parallels of latitude:
Tropic of Cancer (23½° N) in the northern hemisphere.
Tropic of Capricorn (23½° S) in the southern hemisphere.
Arctic Circle at 66½° N of the Equator.
Antarctic Circle at 66½° S of the Equator.
Latitudinal Heat Zones of the Earth
The midday sun is exactly overhead at least once a year on all latitudes between the Tropic of Cancer and the Tropic of Capricorn. This area, therefore, receives the maximum heat and is called the Torrid Zone.
The midday sun never shines overhead on any latitude beyond the Tropic of Cancer and the Tropic of Capricorn. The angle of the sun's rays decreases towards the poles. The areas between the Tropic of Cancer and the Arctic Circle (in the northern hemisphere), and between the Tropic of Capricorn and the Antarctic Circle (in the southern hemisphere), have moderate temperatures. These areas are known as the Temperate Zones.
Areas between the Arctic Circle and the North Pole in the northern hemisphere, and between the Antarctic Circle and the South Pole in the southern hemisphere, are very cold. This is because the sun’s rays are slanting, as the sun does not rise much above the horizon. These regions are called Frigid Zones.
Heat Zones of the Earth
Torrid Zone: Located between the Tropic of Cancer and the Tropic of Capricorn, this zone receives maximum heat.
Temperate Zones: Found between the Tropics and the Arctic/Antarctic Circles, these zones have moderate temperatures.
Frigid Zones: Located between the Arctic Circle and the North Pole, and between the Antarctic Circle and the South Pole, these areas experience very cold temperatures due to slanting sun rays.
Additional Key Points about Latitude
Latitude lines run horizontally across the Earth.
The Equator is at 0° latitude.
The North Pole is at 90° N latitude, and the South Pole is at 90° S latitude.
There are 180 parallels of latitude, with the distance between them decreasing towards the poles.
Longitude is an angular distance, measured in degrees along the Equator east or west of the Prime (or First) Meridian. On the globe, longitude is shown as a series of semi-circles that run from pole to pole passing through the equator. These lines are also called meridians.
Important Longitudes
Unlike the equator, which is centrally placed between the poles, any meridian could have been used to begin numbering the longitude. However, it was finally decided in 1884, by international agreement, to choose the meridian passing through the Royal Astronomical Observatory at Greenwich, near London, as the zero meridian, known as the Prime Meridian (0°).
Meridians of longitude converge at the poles, and as the parallels of latitude shorten towards the poles, the space between meridians also narrows.
Meridians play a critical role in determining local time in relation to Greenwich Mean Time (G.M.T.), sometimes referred to as World Time.
Longitude and Time
Since the Earth makes one complete revolution of 360° in one day or 24 hours, it passes through 15° of longitude in one hour or 1° in 4 minutes.
The Earth rotates from west to east, so as we move eastwards, local time is advanced by 1 hour for every 15°. Conversely, moving westwards, local time is retarded by 1 hour.
Places east of the Prime Meridian (Greenwich) see the sun earlier and therefore gain time, while places west of it see the sun later and lose time.
To calculate the local time, if we know G.M.T., we simply add or subtract the difference in hours based on the longitude.
Longitude
Lines of Longitude run vertically and are known as Meridians.
The Prime Meridian, located in Greenwich, England, is at 0° Longitude.
There are 180° east Longitude and 180° west Longitude.
Longitude and Time
The Prime Meridian in Greenwich has the sun at its highest point at noon.
Earth's rotation causes time differences; places east of Greenwich are ahead of Greenwich time, and places west are behind.
The Earth rotates 360° in 24 hours, passing through 15° in one hour.
Standard Time and Time Zones
If each town were to keep the time of its own meridian, there would be significant differences in local time between one town and another. Travelers moving across the country would have to constantly adjust their watches to keep up with appointments, which would be impractical and inconvenient.
To avoid such difficulties, a system of standard time is followed by all countries.
Most countries adopt their standard time based on the central meridian of their countries.
In larger countries such as Canada, USA, China, and the USSR, it would be impractical to have a single time zone. As a result, these countries have multiple time zones.
Canada and the USA have five time zones: Atlantic, Eastern, Central, Mountain, and Pacific Time Zones. The time difference between the Atlantic and Pacific coasts is nearly five hours.
The USSR had eleven time zones before its disintegration, while Russia now has nine time zones.
Local time varies across longitudes, which is why standard time is necessary for a country.
In India, the standard meridian is 82½° E, and the local time here is called Indian Standard Time (IST).
The Earth is divided into 24 time zones, each covering 15° of longitude.
Chaibagaan Time
About 150 years ago, British colonialists introduced a time schedule called chaibagaan time or bagaan time for tea planters. This time was set one hour ahead of IST to optimize the use of daylight and improve productivity.
After Independence, Assam, along with the rest of India, has been following IST for the past 66 years.
The government of the Indian state of Assam proposed returning to Chaibagaan time to conserve energy and increase productivity. However, the Indian government did not accept this proposal.
The International Date Line
A traveler going eastwards gains time from Greenwich until reaching the meridian 180°E, where he will be 12 hours ahead of G.M.T.. Similarly, when traveling westwards, he loses 12 hours when he reaches 180°W. Therefore, there is a total time difference of 24 hours or a whole day between the two sides of the 180° meridian.
The International Date Line is located at 180° longitude.
Crossing the date line eastwards results in losing a day, while crossing westwards results in gaining a day.
This is the International Date Line, where the date changes by exactly one day when crossed. A traveler crossing the date line from east to west loses a day (due to the time lost), and crossing from west to east gains a day (due to the time gained).
The International Date Line in the mid-Pacific curves from the standard 180° meridian around the Bering Strait, Fiji, Tonga, and other islands. This is to prevent confusion about the day and date in certain island groups that are split by the meridian. Some islands follow Asiatic or New Zealand Standard Time, while others follow American date and time.
Why is the International Date Line drawn in a zigzag manner?
The International Date Line (IDL) passes through the Pacific Ocean. It is an imaginary line, similar to longitudes and latitudes. The time difference on either side of this line is 24 hours, causing the date to change when crossing it.
Some groups of islands, including Polynesia, Melanesia, and Micronesia, fall on either side of the date line. If the line were straight, two regions of the same island country or group could be in different date zones. To avoid confusion, the IDL is drawn through the sea rather than land, creating a zig-zag pattern.
Eclipses
Solar Eclipse: Occurs when the Moon comes between the Earth and the Sun, making part or all of the Sun invisible from Earth. Types include:
Total
Annular
Partial
Hybrid
Lunar Eclipse: Occurs when Earth comes between the Moon and the Sun, casting a shadow on the Moon.
Due to Earth's tilt, regions beyond the Arctic Circle receive sunlight continuously during the summer months. This phenomenon occurs because the North Pole is tilted towards the Sun during summer, placing the Arctic region in the 'zone of illumination' for about six months.
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