1. Two Main Motions of the Earth
- Rotation – Earth spins on its own axis.
- Revolution – Earth revolves around the Sun.
हिंदी: पृथ्वी की दो मुख्य गतियाँ –
Rotation (अपनी धुरी पर घूमना) → दिन और रात
Revolution (सूर्य के चारों ओर चक्कर लगाना) → ऋतुएँ (Seasons)
2. Rotation of the Earth
- Earth rotates from West to East.
- Time taken for one rotation ≈ 24 hours.
- Axis of rotation is an imaginary line joining North Pole & South Pole.
- Because of rotation, we have: Day on the side facing the Sun, Night on the opposite side.
हिंदी: पृथ्वी पश्चिम से पूर्व (West → East) की ओर घूमती है, इसलिए हमें सूर्य पूर्व में उगता और पश्चिम में डूबता दिखता है।
3. Circle of Illumination
The imaginary line which separates the day side and the night side of the Earth is called
the Circle of Illumination.
हिंदी: जो रेखा पृथ्वी के रोशन भाग (Day) और अंधेरे भाग (Night) को अलग करती है, उसे Circle of Illumination कहते हैं।
4. Revolution of the Earth
- Earth moves around the Sun in an elliptical orbit.
- Time taken for one revolution ≈ 365¼ days (1 year).
- To adjust extra ¼ day each year → every 4 years we have a leap year (366 days).
- Revolution + tilt of Earth’s axis = change of seasons.
हिंदी: पृथ्वी सूर्य के चारों ओर एक अंडाकार (elliptical) कक्षा में घूमती है। 4 साल में लगभग 1 दिन extra बनता है, इसलिए 4वें साल में 29 February वाला leap year होता है।
5. Tilt of Earth’s Axis (23½°)
- Earth’s axis is tilted at 23½° to the plane of its orbit.
- Because of this tilt, different parts of the Earth receive different amounts of sunlight during the year.
- This causes summer, winter, spring, autumn in different hemispheres.
हिंदी: अगर पृथ्वी की धुरी झुकी न होती, तो न तो स्पष्ट ऋतुएँ होतीं, न ही दिन–रात की लम्बाई में इतना अंतर आता।
6. Solstices & Equinoxes (Simple NDA View)
- Summer Solstice – around 21 June
• Northern Hemisphere tilted most towards the Sun → Longest day in Northern Hemisphere. - Winter Solstice – around 22 December
• Northern Hemisphere tilted away from Sun → Shortest day in Northern Hemisphere. - Equinoxes – around 21 March & 23 September
• Sun is directly over the Equator → Day & Night are nearly equal everywhere.
हिंदी:
- 21 June – उत्तरी गोलार्ध में सबसे बड़ा दिन (Summer Solstice)
- 22 December – उत्तरी गोलार्ध में सबसे छोटी दिन (Winter Solstice)
- 21 March, 23 September – दिन और रात लगभग बराबर (Equinox)
7. Effects of Earth’s Motions (Summary)
Due to Rotation:
- Day & Night
- Apparent movement of Sun from East to West
- Change of Seasons
- Variation in length of Day & Night
हिंदी Summary:
Rotation → दिन–रात
Revolution + 23½° Tilt → ऋतुएँ + दिन–रात की लम्बाई में अंतर
📘 Practice Questions (NDA Style)
1. Earth rotates on its axis from:
a) East to West b) West to East c) North to South d) South to North
2. Time taken by the Earth to complete one revolution around the Sun is:
a) 24 hours b) 30 days c) 365¼ days d) 12 hours
3. The tilt of Earth’s axis to the plane of its orbit is:
a) 22° b) 23½° c) 30° d) 45°
4. The longest day in the Northern Hemisphere occurs around:
a) 21 March b) 21 June c) 23 September d) 22 December
5. Equal day and night all over the Earth is called:
a) Solstice b) Eclipse c) Equinox d) Rotation
a) East to West b) West to East c) North to South d) South to North
2. Time taken by the Earth to complete one revolution around the Sun is:
a) 24 hours b) 30 days c) 365¼ days d) 12 hours
3. The tilt of Earth’s axis to the plane of its orbit is:
a) 22° b) 23½° c) 30° d) 45°
4. The longest day in the Northern Hemisphere occurs around:
a) 21 March b) 21 June c) 23 September d) 22 December
5. Equal day and night all over the Earth is called:
a) Solstice b) Eclipse c) Equinox d) Rotation
Answers:
1 – b) West to East
2 – c) 365¼ days
3 – b) 23½°
4 – b) 21 June
5 – c) Equinox
1 – b) West to East
2 – c) 365¼ days
3 – b) 23½°
4 – b) 21 June
5 – c) Equinox
Quick Recap | सार
Now you should be able to:
- Recall the most important ideas of this topic.
- Solve typical NDA-style questions from this chapter.
- Spot and avoid common traps used in competitive exams.
Self-check: 3–4 random questions उठा कर देखिए – अगर आसानी से हो रहे हैं, तो chapter strong है।
Common Exam Mistakes | आम गलतियाँ
- Concept ठीक से clear न करना और सीधे रटने की कोशिश करना।
- Question पूरी तरह पढ़े बिना answer mark कर देना।
- Figures, dates, या formulas को last step में verify न करना।
NDA में smart strategy यह है कि आसान वाले सवाल पहले, doubtful बाद में – और silly mistakes से बचना सबसे ज़रूरी है।