# Earth, universe and solar system

> These study notes explain Earth, universe and solar system for the Group 4 / VAO (Combined Civil Services Examination-IV) exam in plain language: the same reviewed notes the TNPSC Guide app shows, published by our editors with their source. Read the key points first, then practise the unit's questions. For exam facts such as dates and vacancies, always check tnpsc.gov.in.

Last updated: 2026-11-02 · By TNPSC Guide editorial team
URL: https://www.tnpscguide.com/exams/group-4/notes/gs-geography-earth-universe

## Why the exam asks this

In the three papers we read, four questions were on this topic. 2022: which of four statements on the Rajasthan, Punjab-Haryana, Ganga and Brahmaputra plains are correct (question 143; final key (i) and (ii) only: the Ganga plain runs to Bangladesh, not Mizoram; most of the Brahmaputra plain is in Assam, not Meghalaya). 2024: three statements on the Himalayas (question 110; final key (i) and (ii) only: the Outer Himalaya is the most discontinuous range); matching Ganymede, Titan, Neptune and Triton (question 103; final key 4 3 2 1). In that question, Titan as the moon with clouds agrees with the textbook; but the green appearance the key gives Neptune is given to Uranus by the Std 6 book, and the statements on Ganymede and Triton are not in the pages read. The question on Aksai Chin (question 182) is also not in the pages read.

## The universe and the Milky Way

The stars and celestial bodies that came from the Big Bang together make the universe; it is also called the cosmos. The study of the universe is cosmology; "cosmos" is a Greek word. About 5 billion years after the Big Bang the Milky Way galaxy formed. Andromeda and the Magellanic Clouds are galaxies near the Earth. A light year is the distance light travels in one year; light travels at 3,00,000 km a second. The word "solar" comes from the Latin word "sol", meaning the Sun god; the solar system is believed to have formed about 4.5 billion years ago.

## The Sun and the two kinds of planet

The Sun holds 99.8 per cent of the total mass of the solar system. It is made of hydrogen and helium; its surface temperature is 6000°C; sunlight takes about 8.3 minutes to reach the Earth. "Planet" means "wanderer". Mercury, Venus, Earth and Mars are the inner (terrestrial) planets; Jupiter, Saturn, Uranus and Neptune are the outer (Jovian, gaseous) planets. The asteroid belt lies between Mars and Jupiter. All planets except Venus and Uranus rotate on their axis from west to east.

## The inner planets

Mercury, nearest to the Sun, is the smallest planet; it has no satellite. Though Mercury is nearer the Sun, Venus is the hottest planet. Venus is like the Earth in size, so the two are "twin planets"; Venus takes 243 days to turn once on its axis; it has no satellite; it is called the morning star and the evening star. The Earth is the third planet from the Sun and the fifth largest; the "blue planet"; the only planet not named after a Roman or Greek god. Its polar diameter is 12,714 km and its equatorial diameter 12,756 km; it goes round the Sun at 30 km a second. Mars is the second smallest planet; iron oxide on its surface makes it the "red planet"; Phobos and Deimos are its two satellites. The Indian Space Research Organisation (ISRO) sent the Mangalyaan craft to study Mars.

## The outer planets

Jupiter is the largest planet of the solar system and the one that spins fastest. Io, Europa, Ganymede and Callisto are some of its largest satellites. Saturn is the second largest planet, with large rings; its density is less than that of water. Saturn's largest satellite is Titan, the only satellite wrapped in an atmosphere of nitrogen and methane and in clouds. Uranus was found by William Herschel in 1781, the first planet found with a telescope; methane makes it look green; its axis is tilted so much that it is the "rolling planet"; its largest satellite is Titania. Neptune is the eighth planet, the farthest from the Sun and the coldest; strong winds blow there; its blue and white colour sets it apart from Uranus; its largest satellite is Triton. The distance between the Sun and the Earth is 150 million km. Do not memorise the number of satellites of each planet; the book's figures are out of date.

## The Moon and Halley's comet

The Moon is 3,84,400 km from the Earth and a quarter of its size. It is the only celestial body on which humans have landed; it has no atmosphere. It takes about 27 days 8 hours both to turn on its axis and to go round the Earth. India's Chandrayaan-1 was launched in 2008. Halley's comet, which comes near the Earth once in 76 years, was last seen in 1986 and will appear again in 2061.

## The Earth's rotation and revolution

The Earth's axis is tilted at 23½°; it makes an angle of 66½° with its orbit. The speed of rotation is 1670 km an hour at the equator, 845 km at 60° north and zero at the poles. One rotation takes 23 hours 56 minutes 4.09 seconds. One revolution round the Sun takes 365¼ days, so once in four years February gets one extra day; that year is a leap year. The point nearest the Sun is perihelion and the farthest is aphelion. On 21 March and 23 September the Sun's rays fall straight on the equator, so day and night are equal; these are the equinoxes. On 21 June the vertical rays fall on the Tropic of Cancer: the summer solstice (the longest day in the northern hemisphere); on 22 December they fall on the Tropic of Capricorn: the winter solstice. The line that divides the lit part from the dark part is the terminator line.

## The Earth's interior

The Earth's interior has three parts: crust, mantle and core. The crust is 5 to 30 km thick; it is rich in silica and aluminium, so it is "SIAL". The mantle is about 2900 km thick. The core is rich in nickel and iron, so it is "NIFE"; the inner core is solid and the outer core liquid.

## India's location and size

India is the world's seventh largest country by area and Asia's second; its land area is 32,87,263 sq km. India lies from 8°4' N to 37°6' N latitude and from 68°7' E to 97°25' E longitude. India's southern tip is Indira Point (formerly Pygmalion), at 6°45' N in the Andaman and Nicobar Islands. The southern tip of the mainland is Cape Comorin (Kumari Munai); the northern tip is Indira Col. From Indira Col in the north to Kanyakumari in the south is 3214 km; from the Rann of Kutch in the west to Arunachal Pradesh in the east is 2933 km. India has 28 states and 8 union territories.

## Borders and Indian Standard Time

India's land border is 15,200 km; the longest is with Bangladesh (4,156 km) and the shortest with Afghanistan (106 km). The mainland coastline is about 6,100 km; with the islands it is 7,516.6 km; these are the book's figures, so do not hold them as the answer to a question about now. The Palk Strait separates India and Sri Lanka. The local time of the 82°30' E meridian through Mirzapur (Allahabad) is Indian Standard Time; it is 5 hours 30 minutes ahead of Greenwich time. The Sun rises two hours earlier in Arunachal Pradesh than in Gujarat. Example: sunrise differs from place to place, yet clocks in Chennai and Coimbatore show the same Indian Standard Time.

## The Himalayas

The Himalayas are the world's youngest and highest fold mountains, about 2500 km long from the Indus valley to the Brahmaputra valley. The Sanskrit word "Himalaya" means "abode of snow". The Pamir Knot is "the roof of the world". The Eurasian landmass in the north and the Gondwana landmass in the south moved towards each other, so the Tethys Sea between them was folded and the Himalayas formed. The Trans Himalaya (the western or Tibetan Himalaya) lies north of the Himalayas; the Zaskar, Ladakh, Kailash and Karakoram are its main ranges. Unlike the young Himalayas, the Aravalli range is one of the oldest fold mountain ranges in the world.

## The three Himalayan ranges

The Greater Himalaya (Himadri) is 25 km wide and 6000 m high on average; it gets less rain than the Lesser Himalaya and the Siwaliks. Everest (8848 m, Nepal) and Kangchenjunga, between Nepal and Sikkim, are here. Nine of the world's 14 highest peaks are in the Himalayas. The Greater Himalaya is more continuous than the other ranges; the Gangotri, Yamunotri and Siachen glaciers are here. The Lesser Himalaya (Himachal) is 80 km wide on average and 3700-4500 m high; the Pir Panjal, Dhauladhar and Mahabharat ranges and the hill stations of Shimla, Mussoorie, Nainital, Almora, Ranikhet and Darjeeling are here. The Outer Himalaya (Siwaliks) is 900-1100 m high and the most discontinuous range. The long valleys between the Lesser and Outer Himalaya are called Duars in the east and Duns in the west.

## Passes

The Himalayan passes: Karakoram (Jammu and Kashmir); Zoji La; Shipki La; Bomdi La (Arunachal); Nathu La and Jelep La (Sikkim). The Khyber Pass, linking Pakistan and Afghanistan, and the Bolan Pass in Pakistan are important passes of the Indian subcontinent. The book does not give Zoji La's state clearly; do not take it as an answer.

## The northern plains

The northern plains have the Bhabar (a porous belt of coarse sand), the Terai (a wet, forested belt), the Bhangar (old alluvial uplands) and the Khadar (new alluvium, bet land); the raised areas are chars and the marshy areas bils. The Rajasthan plain lies west of the Aravallis and covers about 1,75,000 sq km. The Thar desert, with 2 lakh sq km, is the world's 7th largest desert and the natural border between India and Pakistan. The Punjab-Haryana plain, north-east of the Indian desert, was formed by deposits of the Sutlej, Beas and Ravi. The Ganga plain, from the Yamuna in the west to Bangladesh in the east, covers about 3.75 lakh sq km and is India's largest plain. Most of the Brahmaputra plain is in Assam.

## The peninsular plateau and the coasts

The peninsular plateau covers about 16 lakh sq km, about half the country, and is India's largest natural division. Anamudi (2695 m) in the Anaimalai is its highest peak. The Narmada divides it into the Central Highlands and the Deccan Plateau. The western part of the Central Highlands is the Malwa plateau; its eastern extension is Bundelkhand and Baghelkhand. The Chota Nagpur plateau in the north-east is known for iron ore and coal. The highest peak of the Aravallis is Guru Shikhar (1722 m). The northern part of the Western Ghats is the Sahyadri; the Eastern Ghats are also called the Purvadri; the two meet in the Nilgiris. From the north, the west coast is called Konkan, Kanara and Malabar. On the east coast, the part between the Mahanadi and the Krishna is the Northern Circars and the part between the Krishna and the Kaveri the Coromandel coast.

## Islands

The Andaman and Nicobar Islands, 572 islands in the Bay of Bengal, and Lakshadweep in the Arabian Sea are India's islands. India's only active volcano is Barren Island. The 10° Channel separates the Andamans from the Nicobars, and the 8° Channel separates Lakshadweep from the Maldives. Port Blair is the administrative capital of the Andaman and Nicobar Islands. Kavaratti is the capital of Lakshadweep, which is made of coral. The Laccadive, Minicoy and Amindivi groups have been called Lakshadweep since 1973.

## Tamil Nadu: location and size

Tamil Nadu lies from 8°4' to 13°35' N latitude and from 76°18' to 80°20' E longitude. Its extreme points: Kodiakarai in the east, Anaimalai in the west, Pulicat Lake in the north and Kanyakumari in the south. Its area is 1,30,058 sq km; the book calls it India's eleventh largest state. By the book, after Gujarat and Andhra Pradesh, Tamil Nadu has India's third longest coastline, 906.9 km; do not hold either of these two state ranks as the answer to a question about now. The Std 10 book gives its divisions by relief as the Western Ghats, the Eastern Ghats, the plateaus, the coastal plains and the inland plains; the same unit's summary says three major divisions, so do not take "how many divisions" as an answer.

## The hills of Tamil Nadu

The highest peak of the Nilgiris is Doddabetta (2,637 m); Mukurthi is 2,554 m; the highest peak of the Palani hills is Vandaravu (2,533 m). The Palghat, Shencottah, Aralvaimozhi and Achankovil passes are the main passes of the Western Ghats. The Eastern Ghats are broken hills; in Tamil Nadu they are the Javadhu, Shevaroy, Kalvarayan, Kolli and Pachamalai hills. Solaikaradu (1,620 m) in the Shevaroys is the highest peak of the southern Eastern Ghats; Yercaud, "the poor man's Ooty", is in these hills.

## Geographical landmarks: oceans, straits and channels (B2-16)

The Pacific is the largest and deepest ocean (about 168.72 million sq km); its Mariana trench (10,994 m) is the deepest part of the Earth, and its ring of volcanoes makes it the 'Ring of Fire'. The deepest part of the 'S'-shaped Atlantic is the Milwaukee deep; of the triangular Indian Ocean, the Java trench (7,725 m); of the Southern Ocean, the South Sandwich trench; of the smallest, the Arctic, the Eurasian basin. Straits: the Bering joins the Pacific and the Arctic, the Gibraltar the Atlantic and the Mediterranean, the Malacca the Indian Ocean and the Pacific, the Palk the Bay of Bengal and Palk Bay. Channels: 6° Indira Point–Indonesia, 8° Maldives–Minicoy, 9° Lakshadweep–Minicoy, 10° Andaman–Nicobar. Easy to confuse: Minicoy comes in both 8° and 9°; only 8° comes with the Maldives.

## Geographical landmarks: falls, deserts, lakes and peaks (B2-16)

The highest waterfall in the world is Angel Falls in Venezuela (979 m); Niagara is on the Canada–USA border and the Victoria Falls on the Zambia–Zimbabwe border. Africa: the Sahara (9.2 million sq km, 11 countries; Egypt's Qattara depression 133 m below sea level); the Sahel, whose name means 'border'; Lake Victoria, source of the Nile; Tanganyika, the world's longest freshwater lake; Kilimanjaro 5895 m; the Nile, 6650 km long. Australia: Ayers Rock (Uluru, 863 m), the Great Victoria desert, the salt Lake Eyre, Kosciuszko 2230 m, the Murray, 2508 km long. Antarctica: Vinson Massif 5140 m and the Lambert glacier, the largest in the world. Easy to confuse: 'Victoria' names a lake (Africa), a waterfall (Zambia–Zimbabwe) and a desert (Australia).

**Example: Matching deserts with places**

match (a) Sahara (b) Sahel (c) Great Victoria (d) Thar with 1. Australia 2. India 3. northern Africa 4. the belt between the Sahara and the savanna.

1. The Sahara is in northern Africa: a – 3.
2. 'Sahel' means 'border'; it lies between the Sahara and the savanna to its south: b – 4.
3. The Great Victoria is Australia's largest desert: c – 1.
4. The Thar desert is in the Rajasthan plain: d – 2.

Answer: 3 4 1 2.

**Key numbers**

| | |
| --- | --- |
| Mass held by the Sun; time for sunlight to reach the Earth | 99.8%; about 8.3 minutes (class 6, page 162) |
| Uranus found by Herschel | 1781 (class 6, page 166) |
| Distance to the Moon; Chandrayaan-1 | 3,84,400 km; 2008 (class 6, page 167) |
| Halley's comet | once in 76 years; 1986, 2061 (class 6, page 167) |
| Tilt of the Earth's axis; time for one revolution | 23½°; 365¼ days (class 6, page 168-169) |
| Equinoxes; solstices | 21 March, 23 September; 21 June, 22 December (class 6, page 169-170) |
| India's area; rank | 32,87,263 sq km; seventh in the world (class 10, page 138) |
| Land border; coastline with islands | 15,200 km; 7,516.6 km (class 10, page 138) |
| Indian Standard Time | 82°30' E; 5 hours 30 minutes ahead of Greenwich (class 10, page 139) |
| Everest; Anamudi; Guru Shikhar | 8848 m; 2695 m; 1722 m (class 10, page 142, 145) |
| Andaman and Nicobar Islands | 572 (class 10, page 146) |
| Tamil Nadu's area; coastline | 1,30,058 sq km; 906.9 km (class 10, page 213) |
| Doddabetta; Solaikaradu | 2,637 m; 1,620 m (class 10, page 215, 216) |

> **Exam tip:** Memory hooks
What marks each planet: "smallest Mercury, hottest Venus, largest Jupiter, rings Saturn, green Uranus, blue-and-white Neptune". Two spin the other way: "Venus and Uranus". Say the Himalayas from the north as "Himadri, Himachal, Siwalik": heights 6000, 3700-4500 and 900-1100 m. Channels: "ten for the Andamans, eight for the Maldives". Alluvium: "Bhangar old, Khadar new".

**Easy to confuse**

| | |
| --- | --- |
| Asteroid / dwarf planet | சிறுகோள் / குறுங்கோள்; the book uses குறுங்கோள் for both, but here only these two words are used |
| Mercury / Venus | nearest the Sun and smallest / hottest |
| Uranus / Neptune | green (methane), the rolling planet / blue and white, the coldest |
| Titan / Titania / Triton | Saturn's satellite wrapped in clouds / Uranus's largest satellite / Neptune's largest satellite |
| India's southern tip / the mainland's southern tip | Indira Point (6°45', Nicobar) / Cape Comorin |
| Greater Himalaya / Outer Himalaya | continuous, less rain / the most discontinuous; Duars and Duns |
| Bhangar / Khadar | old alluvium / new alluvium |
| 10° Channel / 8° Channel | Andaman-Nicobar / Lakshadweep-Maldives |
| Anamudi / Doddabetta | highest peak of the peninsular plateau / highest peak of the Nilgiris; the book does not call Doddabetta "Tamil Nadu's highest peak" |
| Kangchenjunga | between Nepal and Sikkim; do not take the height the book prints as an answer |

> **Exam tip:** Quick check
1. Which was the first planet found with a telescope? Answer: Uranus (1781, William Herschel).
2. Indian Standard Time is the local time of which meridian? Answer: 82°30' E, through Mirzapur.
3. Which Himalayan range is the most discontinuous? Answer: the Outer Himalaya (Siwaliks).
4. What is India's only active volcano? Answer: Barren Island.
5. In which hills is "the poor man's Ooty"? Answer: the Shevaroy hills (Yercaud).

Source: சமூக அறிவியல், ஆறாம் வகுப்பு, முதல் பருவம், தொகுதி 3, தமிழ் வழி (Social Science, Standard VI, Term I, Volume 3, Tamil medium; Samacheer Kalvi) (6ஆம் வகுப்புச் சமூக அறிவியல் (பருவம் 1), புவியியல் அலகு 1 (பேரண்டம் மற்றும் சூரியக் குடும்பம்), பக்கம் 160-170; 10ஆம் வகுப்புச் சமூக அறிவியல், புவியியல் அலகு 1 (இந்தியா – அமைவிடம், நிலத்தோற்றம் மற்றும் வடிகாலமைப்பு), பக்கம் 138-147, அலகு 6 (தமிழ்நாடு – இயற்கைப் பிரிவுகள்), பக்கம் 213-216; 9ஆம் வகுப்புச் சமூக அறிவியல், புவியியல் அலகு 1 (நிலக்கோளம் – I புவி அகச்செயல்பாடுகள்), பக்கம் 171-172; 6ஆம் வகுப்பு பருவம் 1 புவியியல் அலகு 2, பக்கம் 181-185; 7ஆம் வகுப்பு பருவம் 1 புவியியல் அலகு 2, பக்கம் 171; 8ஆம் வகுப்பு புவியியல் அலகு 7, பக்கம் 166-180; 9ஆம் வகுப்பு புவியியல் அலகு 2, பக்கம் 183)

## Sources

- [Official syllabus page](https://www.tnpsc.gov.in/english/syllabus.html)
- [Notifications](https://www.tnpsc.gov.in/English/Notification.aspx)