Longitudes & Time zones - Delhi Police Constable PDF Download

Earth's Structure and Size

The Earth is a slightly flattened, oblate spheroid with a diameter of approximately 12,742 kilometers (7,917 miles) and a circumference of 40,075 kilometers (24,901 miles) around the equator. It is composed of various layers, including the atmosphere divided into six distinct regions – the troposphere, stratosphere, mesosphere, thermosphere, exosphere, and ionosphere. The Earth's surface is predominantly covered by water, accounting for about 71% of its total area, with the remaining 29% comprising landmasses.

Earth's Motion: Rotation and Revolution

• The Earth is constantly in motion, revolving around the Sun and rotating on its axis. The rotation, occurring from west to east (counter-clockwise), causes day and night, with one complete rotation taking approximately 24 hours. This rotation is not perfect; instead, the Earth's axis is tilted at about 23.5 degrees, giving rise to the changing seasons as it revolves around the Sun.
• The revolution around the Sun, completing one full orbit in approximately 365.25 days, leads to the different seasons experienced across the globe. The Earth's orbit is not a perfect circle, but an ellipse, resulting in variations in its distance from the Sun. This variation creates the phenomena of perihelion (closest to the Sun) and aphelion (farthest from the Sun), occurring around January 3 and July 4, respectively.

Leap Year: Adjusting the Calendar

To synchronize the calendar year with the time it takes the Earth to orbit the Sun, we have leap years. In an ordinary year, there are 365 days, but approximately every four years, we add an extra day to February, making it a leap year with 366 days.

Latitudes and Longitudes: The Grid System

To precisely locate any point on Earth's surface, geographers use a grid system of latitude and longitude. Latitudes are the east-west lines that run parallel to the equator, ranging from 0 degrees (Equator) to 90 degrees at both the North Pole (90 degrees North) and South Pole (90 degrees South). Longitudes, on the other hand, are the north-south lines that meet at the poles and are measured from the Prime Meridian at 0 degrees to 180 degrees East or West.

Major Latitudinal Lines

• Equator: The longest latitude, dividing the Earth into the Northern and Southern Hemispheres.
• Arctic Circle: Located at 66.5 degrees North, marking the northernmost circle.
• Antarctic Circle: Found at 66.5 degrees South, representing the southernmost circle.
• Tropic of Cancer: Positioned at 23.5 degrees North, where the Sun is directly overhead during the June solstice.
• Tropic of Capricorn: Situated at 23.5 degrees South, experiencing the Sun's direct overhead rays during the December solstice.

Geographical Zones on Earth

The different latitudinal zones correspond to distinct climatic conditions and are as follows:

• Frigid Zones: The areas between the poles and the Arctic and Antarctic Circles, experiencing extremely cold temperatures.
• Temperate Zones: Found between the Arctic and Antarctic Circles and the Tropics, featuring moderate weather with distinct seasons.
• Torrid Zones: The regions between the Tropic of Cancer and the Tropic of Capricorn, characterized by hot climates with little seasonal variation.

The Prime Meridian and Standard Time Zones

• The Prime Meridian, passing through the Greenwich Royal Observatory in London, serves as the reference line for longitudes. The Earth is divided into 24 time zones, each covering 15 degrees of longitude, with local time synchronized with the central meridian of each time zone. The International Date Line, located at the 180-degree longitude, marks the transition between consecutive calendar days.
• Standard time zones are crucial for global coordination, ensuring uniformity in timekeeping and avoiding confusion during travels across different regions.