for Telugu Explanation https://manajournal.blogspot.com/2026/02/for-english-explaination.html

(Geography Notes for UPSC & State PSC Exams)

For clear explanations, UPSC & State PSC study content, and useful digital knowledge — follow my YouTube channel and support the journey!

👉 Subscribe now: https://youtube.com/@digitalstories-r5k?si=LKQvAr5-SY1cbN7v

Prepare Smart. Crack UPSC/Groups Exams with Confidence!

Buy Best Geography Books Here

👉 https://amzn.to/4tB89fG

👉 https://amzn.to/3Q7PLwe

Motions of the Earth:

The Earth is a dynamic planet and part of the solar system. It is not stationary but continuously moves. These movements are mainly of two types:

Rotation (Daily Motion)
Revolution (Annual Motion)

These motions are responsible for day and night, seasons, and variation in the length of day and night.

1. Rotation of the Earth:

What is Rotation?

Rotation refers to the spinning of the Earth on its own axis from west to east.

Time taken: 24 hours
Also called: Daily Motion
Result: Day and Night

How Does Day and Night Occur?

When the Earth rotates:

The side facing the Sun experiences daylight
The opposite side experiences darkness (night)

Thus, rotation causes the regular cycle of day and night.

2. Revolution of the Earth:

What is Revolution?

Revolution refers to the movement of the Earth around the Sun in an elliptical orbit.

Time taken: 365 days and 6 hours
Also called: Annual Motion
Result: Seasons

The extra 6 hours every year are adjusted by adding one extra day every four years (Leap Year).

Difference Between Rotation and Revolution:

Rotation	Revolution
Movement on axis	Movement around Sun
Takes 24 hours	Takes 365¼ days
Causes Day & Night	Causes Seasons

Variation in Length of Day and Night:

The length of day and night is not the same throughout the year. This happens because:

The Earth's axis is tilted at 23½°
The Earth revolves around the Sun with this tilt

This causes seasons and changes in day length.

Important Dates:

Equinoxes:

21 March
23 September

On these days:

Sun is vertically overhead at the Equator
Day and night are equal everywhere on Earth

Summer Solstice – 21 June:

Sun is vertically overhead at the Tropic of Cancer (23½° N)
Northern Hemisphere experiences:
- Longest day
- Shortest night

Winter Solstice – 22 December:

Sun is vertically overhead at the Tropic of Capricorn (23½° S)
Southern Hemisphere experiences:
- Longest night
- Shortest day

Special Polar Regions:

Beyond:

Arctic Circle (66½° N)
Antarctic Circle (66½° S)

There can be:

Continuous daylight for 6 months
Continuous darkness for 6 months

Structure of the Earth:

The Earth is made up of several layers. It is not a single solid mass of rock but consists of different zones arranged from the surface to the center. These layers differ in thickness, composition, and physical state.

The Earth is divided into three major layers:
Crust (SIAL)
Mantle (SIMA)

Core

1. Crust (SIAL):

The crust is the outermost layer of the Earth.
Thickness in continents: About 33 km
Thickness in ocean basins: 5–10 km

The continental crust is thicker than the oceanic crust.

The crust mainly consists of Silica and Aluminium, therefore it is also called SIAL.

The crust is not a continuous solid rock mass. It is broken into large pieces called tectonic plates, which float over a semi-molten layer called the Asthenosphere.

2. Mantle (SIMA):

The mantle is the layer of rock below the crust.
Total thickness: About 2900 km
It contains most of the Earth's mass.
Most of the Earth's internal heat is located here.
It is mainly composed of Ferro-magnesium silicates.
Because of silica and magnesium content, it is called SIMA.

The mantle is divided into two parts:

(a) Upper Mantle:

Thickness: About 650 km
The top part of the upper mantle is solid.
Together with the crust, it forms the Lithosphere.
The lithosphere makes up the Earth’s tectonic plates.

Within the upper mantle lies the Asthenosphere, a semi-molten layer where rocks flow slowly. This layer allows tectonic plates to move.

(b) Lower Mantle:

Thickness: About 2700 km
It is solid in nature.
Temperatures are very high.
However, due to extreme pressure, the rocks do not melt.

3. Core:

The core is the innermost layer of the Earth.

It is divided into: Inner Core Outer Core

(a) Outer Core

Thickness: About 1900 km It is in a liquid state Composed mainly of molten iron and nickel Extremely high temperature

The liquid outer core is responsible for generating and controlling the Earth’s magnetic field.

(b) Inner Core:

Thickness: About 1600 km
It is in a solid state
Composed mainly of solid iron and nickel
Temperature: Around 5,500°C
Pressure: About 4 million atmospheres

Even though the temperature is extremely high, the inner core remains solid due to immense pressure.
if you want listen all this content in telugu. you can watch this video:

Practice MCQs:

The Earth completes one rotation in:
a) 12 hours
b) 24 hours
c) 365 days
d) 30 days
On which date does the Summer Solstice occur?
a) 21 March
b) 23 September
c) 21 June
d) 22 December

(Answers: 1-xxx, 2-xxx,comment below )

Disclaimer:

This content is prepared for educational and informational purposes only. The notes are simplified for better understanding and exam preparation (UPSC and State Exams). Readers are advised to refer to standard textbooks and official sources for detailed study.

Pages

Wednesday, February 18, 2026

Chapter 1.1 Motions of the Earth – Rotation and Revolution,Structure of the Earth.