1. The Universe & Galaxies
The Universe contains billions of galaxies.
Our galaxy is **Milky Way**, and the Sun is one of its stars.
हिंदी: Universe = ब्रह्माण्ड, Milky Way = आकाशगंगा (जहाँ हमारा Solar System स्थित है)
2. Solar System (Sun + 8 Planets)
Order of planets from the Sun:
Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune
Important Points:
Important Points:
- Sun = 99.86% mass of the whole Solar System.
- Earth is the 3rd planet and the only known planet with life.
- Jupiter = biggest planet; Mercury = smallest.
हिंदी: याद करने की ट्रिक – “मेरी बहुत आसान माँ ने जग को सही उठाया”
(ME-VE-EA-MA-JU-SA-UR-NE)
3. Earth’s Shape & Structure
- Earth’s shape = **Oblate Spheroid** (not perfectly round).
- Equator bulges outward slightly.
- Poles are slightly flattened.
हिंदी: पृथ्वी गोल है लेकिन बीच में उभरी और ध्रुवों पर थोड़ी दबाई हुई है।
4. Important Motions of Earth
- Rotation – Earth spins on its axis (24 hours) → Day & Night.
- Revolution – Earth orbits around the Sun (365¼ days) → Seasons.
- Earth’s axis is tilted at **23.5°** → unequal day lengths.
हिंदी: 23.5° का झुकाव = ऋतुएँ, दिन-रात की लम्बाई में बदलाव का कारण।
5. Satellites (Natural & Artificial)
- Moon = Earth’s **only natural satellite**.
- Artificial satellites = man-made (INSAT, GSAT, CartoSAT etc.).
📘 Practice Questions (NDA Style)
1. Which is the largest planet in our Solar System?
a) Earth b) Jupiter c) Saturn d) Neptune
2. Earth’s axis is tilted at:
a) 22° b) 23.5° c) 30° d) 15°
3. The shape of the Earth is best described as:
a) Perfect sphere b) Flat c) Oblate spheroid d) Ellipse
a) Earth b) Jupiter c) Saturn d) Neptune
2. Earth’s axis is tilted at:
a) 22° b) 23.5° c) 30° d) 15°
3. The shape of the Earth is best described as:
a) Perfect sphere b) Flat c) Oblate spheroid d) Ellipse
Answers:
1 – b) Jupiter
2 – b) 23.5°
3 – c) Oblate spheroid
1 – b) Jupiter
2 – b) 23.5°
3 – c) Oblate spheroid
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।