Motions of the Earth
Overview
Earth moves in two ways: on its own axis (rotation) and around the Sun (revolution). Rotation creates day and night, while revolution creates the year and seasons. These two movements are like Earth's internal clock.
Typed Notes
Rotation — The Clock of Day and Night
Earth spins on an imaginary axis — this is called rotation. One complete spin takes about 24 hours — and this is what creates day and night. Earth spins from west to east (if viewed from above, it moves anti-clockwise). Because of this, the Sun, Moon, and stars all appear to rise in the east and set in the west. We do not feel Earth spinning because we are moving along with it — just like when you sit in a train, the objects outside appear to be moving past you.
Revolution and Leap Year
Earth completes one orbit around the Sun in about 365 days and 6 hours (365¼ days) — this is called revolution. This path is slightly oval (ellipse) in shape. Every year, those 6 hours keep adding up, and after 4 years they total one full day — which is added to February. That is why every 4th year, February has 29 days and the year has 366 days — this is called a leap year. For example: 2020, 2024, 2028.
Axis Tilt and Seasons
Earth's axis is not straight — it is tilted at 23½° and always points in the same direction as Earth moves around the Sun. When Earth is at a position where the Northern Hemisphere faces toward the Sun — sunlight falls more directly there and it is summer; at the same time, the Southern Hemisphere is tilted away — so it is winter there. As Earth continues its orbit and the position changes — the seasons change too. This is why the real cause of seasons is not Earth's distance from the Sun, but the tilt of its axis.
Circle of Illumination
Because Earth is round and light travels in straight lines, the entire Earth is never lit up at once — only the half facing the Sun is illuminated at any time. The large circle that separates the lit half from the dark half is called the circle of illumination. As Earth rotates along with this circle, different places experience sunrise and sunset at different times.
Key Concepts
Revision ke liye ek nazar — exam se pehle yahi padhna hai.
- 01Rotation: Earth spins on its imaginary axis once in 24 hours (1 day) — this creates day and night. Earth appears to spin from west to east, which is why the Sun rises in the east.
- 02Revolution: Earth completes one orbit around the Sun in 365 days and 6 hours (365¼ days) — this makes 1 year. Every 4th year, those 6 hours add up to 1 full day — giving us a leap year (February has 29 days).
- 03Earth's orbit is slightly oval (ellipse) in shape. While moving, Earth's axis stays tilted at 23½° — this tilt is the real reason for seasons.
- 04Seasons: In the Northern Hemisphere, when the axis tilts toward the Sun — it is summer; when it tilts away — it is winter. Spring and autumn are the in-between stages.
- 05Circle of illumination: The circle that divides Earth into the lit and dark halves — at any given time, only half of Earth is illuminated.
Questions & Solutions
Pehle khud try karo — phir solution kholo. Yahi tariqa topper banata hai.
How are day and night formed?
Why does a leap year occur?
What is the real cause of seasons — Earth's distance from the Sun or its axis tilt?
What is the circle of illumination?
Why does the Sun always rise in the east?
Rotation (24 hours, on its axis) = day and night. Revolution (365¼ days, around the Sun) = year + leap year. The 23½° axis tilt is the real cause of seasons. The circle of illumination divides Earth into its lit and dark halves.
Chapter-end quiz
4 MCQsOption tap karo — turant pata chalega sahi ya galat, explanation ke saath.
Q1.How long does Earth take to complete one spin on its axis?
Q2.How many days does February have in a leap year?
Q3.In how many days does Earth complete one orbit around the Sun?
Q4.What is the real cause of seasons?
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