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

Size and Shape of the Earth

Motions of the Earth

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.

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 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.

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.

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.

Important Parallels of Latitude

Latitudinal Heat Zones of the Earth

Heat Zones of the Earth

Additional Key Points about Latitude

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

Longitude and Time

Longitude

Longitude and Time

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.

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.

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.

Why is the International Date Line drawn in a zigzag manner?

Eclipses

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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