Geography - Earth, Environment & Resources • Topic 1 of 4

Planet Earth & the Globe

The Earth is the third planet from the Sun and the only one known to support life, thanks to the right temperature, water and oxygen-rich air. It is not a perfect sphere but a geoid - slightly flattened at the poles and bulging at the Equator. A globe is a true small-scale model of the Earth. The Earth has two main motions. Rotation is the spinning of the Earth on its imaginary axis from west to east, completed in about 24 hours, and it gives us day and night - the half facing the Sun has day, the half turned away has night. Revolution is the Earth's movement around the Sun in an elliptical orbit, taking about 365.25 days (one year; the extra quarter-days add up to a leap year of 366 days every four years). Because the Earth's axis is tilted at 23.5 degrees, different parts receive direct sunlight at different times of the year, which causes the seasons. To locate places, geographers use a grid. Latitudes are imaginary horizontal lines (parallels) measured in degrees north or south of the Equator (0 degrees); the important ones are the Tropic of Cancer (23.5 N), the Tropic of Capricorn (23.5 S), and the Arctic and Antarctic Circles (66.5 N and S). Longitudes are vertical lines (meridians) running pole to pole, measured east or west of the Prime Meridian (0 degrees, through Greenwich). Because the Earth turns 360 degrees in 24 hours, it covers 15 degrees of longitude every hour - the basis of time zones. India follows a single Indian Standard Time based on the 82.5 degrees E meridian.

✅ Solved examples

1. The spinning of the Earth on its axis from west to east, completed in about 24 hours, is called rotation. What does rotation cause?
Day and night. The half of the Earth facing the Sun experiences day, while the half turned away experiences night.
2. What is the primary cause of the change of seasons on the Earth?
The tilt of the Earth's axis (23.5 degrees) combined with its revolution around the Sun. The tilt makes different regions receive direct sunlight at different times of the year. It is NOT caused by changes in distance from the Sun.
3. The Equator is the most important line of latitude. What is its value in degrees, and what does it divide the Earth into?
The Equator is 0 degrees latitude. It divides the Earth into the Northern Hemisphere and the Southern Hemisphere.
4. Indian Standard Time (IST) is calculated on the basis of which longitude?
82.5 degrees E longitude, which passes near Mirzapur (Uttar Pradesh). IST is ahead of Greenwich Mean Time by 5 hours 30 minutes.

✏️ Practice — try these, take hints as needed

1. The Earth's true shape is best described as a:
Not a perfect sphere.
Flattened at the poles, bulging at the Equator.
Geoid (an oblate spheroid)
2. The imaginary line of 0 degrees longitude passing through Greenwich is called the:
The reference line for longitudes.
Runs from pole to pole.
Prime Meridian
3. The Earth completes one revolution around the Sun in approximately:
This defines one year.
About 365 and a quarter days.
365.25 days (about one year)
4. The Tropic of Cancer is located at which latitude?
North of the Equator.
23.5 degrees.
23.5 degrees North

📝 Topic test — 8 questions

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