The solar system is the Sun and everything that goes round it: eight planets and their moons, dwarf planets, asteroids and comets. Beyond it lie the stars, so far away that we measure their distance in light years. Exams ask planet records, the cause of eclipses, satellites, and India's space milestones from Aryabhata to Chandrayaan-3.
On this page you will learn:
- The Sun, the planets in order and each planet's record
- The Moon, its phases, and solar and lunar eclipses
- Stars, light years, the Milky Way, comets and meteors
- Geostationary and polar satellites, IRS and NavIC
- ISRO's people, places and missions, with dates
The Sun and the planets
Rule in one line: the Sun is a star; eight planets go round it in orbits.
The Sun is the star nearest to us. It is a huge ball of hot gas, mostly hydrogen and helium. In its core, hydrogen nuclei join to form helium. This is nuclear fusion, and it releases enormous energy. The Sun is about 1.5 × 10⁸ km away; its light takes about 8 minutes 20 seconds to reach us.
Planets from the Sun: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune — My Very Efficient Mother Just Served Us Nuts.
| Planet | What examiners ask |
|---|---|
| Mercury | Closest to the Sun; smallest planet; no moon |
| Venus | Hottest and brightest; Earth's twin (similar size); spins east to west; no moon |
| Earth | Blue planet; only known home of life; one moon |
| Mars | Red planet (iron oxide); two small moons |
| Jupiter | Largest planet; shortest day; Great Red Spot |
| Saturn | Bright rings; less dense than water |
| Uranus | Tilted on its side; spins east to west |
| Neptune | Farthest planet; longest year (about 165 Earth years) |
Until 2006, Pluto was the ninth planet. In 2006 the International Astronomical Union set a new rule for a planet, and Pluto became a dwarf planet. Ceres and Eris are dwarf planets too. So there are now eight planets.
The Moon and eclipses
Rule in one line: solar eclipse = Moon in the middle (new moon); lunar eclipse = Earth in the middle (full moon).
The Moon is Earth's only natural satellite, about 384,000 km away. It has no light of its own; it reflects sunlight. It has no atmosphere, so there is no sound or weather. Its gravity is about 1/6 of Earth's. We always see the same face, because it spins once in the time it takes to go round Earth once.
- New moonMoon not seen
- WaxingBright part grows
- Full moonWhole face lit
- WaningBright part shrinks
Stars, galaxies and small bodies
Rule in one line: a light year is a distance, and our Sun is one star of the Milky Way.
Stars are hot balls of gas that make their own light. A light year is the distance light travels in a year, about 9.46 × 10¹² km. It measures distance, not time. Billions of stars form a galaxy. Our solar system is in the Milky Way galaxy (Akash Ganga).
| Body | What it is |
|---|---|
| Asteroids | Rocky bits, mostly in a belt between Mars and Jupiter |
| Comets | Ice and dust; grow a tail near the Sun that points away from it |
| Meteors | Burn up in the air; called shooting stars |
| Meteorites | Pieces big enough to reach the ground |
Stars seem to move east to west because Earth spins west to east. The Pole Star sits almost above Earth's axis in the north, so it seems fixed. Two end stars of Saptarishi (Ursa Major, the Big Dipper) point to it. Stars twinkle; planets do not.
Satellites and navigation
Rule in one line: a geostationary satellite goes round once a day, so it seems to hang over one spot.
Indian Remote Sensing (IRS) satellites photograph Earth from space. They help find minerals and groundwater, check crop health, map forests and track floods. They are not used for telephone calls or traffic control.
| System | Country |
|---|---|
| GPS | USA |
| GLONASS | Russia |
| Galileo | Europe |
| NavIC (IRNSS) | India |
ISRO: people, places and first steps
Rule in one line: Sarabhai founded it, Bengaluru runs it, Sriharikota launches it.
| Centre | Place |
|---|---|
| ISRO headquarters | Bengaluru, Karnataka |
| Satish Dhawan Space Centre (SHAR) — launch site | Sriharikota, Andhra Pradesh |
| Vikram Sarabhai Space Centre (rockets) | Thiruvananthapuram, Kerala |
| Semi-Conductor Laboratory | Mohali (SAS Nagar), Punjab, next to Chandigarh; now under MeitY, not ISRO |
| Bhabha Atomic Research Centre (not ISRO) | Trombay, Mumbai |
- 1962INCOSPAR set up
Indian space research begins under Vikram Sarabhai, the father of India's space programme.
- 1963First rocket from Thumba
A sounding rocket from near Thiruvananthapuram.
- 1969ISRO founded
15 August 1969.
- 1975Aryabhata
India's first satellite, launched on 19 April 1975 by a Soviet rocket.
- 1981APPLE
India's first experimental geostationary communication satellite.
- 1984Rakesh Sharma
First Indian in space, on a Soviet mission.
- 1997Kalpana Chawla
First India-born woman in space, on the US shuttle Columbia.
India's missions, with dates
Rule in one line: learn each mission with its year — papers ask the year.
- 2008Chandrayaan-1
India's first Moon mission; it found signs of water on the Moon.
- 2013–14Mangalyaan (Mars Orbiter Mission)
Launched November 2013; reached Mars orbit in September 2014, at the first attempt.
- 2019Chandrayaan-2
Launched 22 July 2019. The orbiter worked; the Vikram lander crashed in September 2019.
- 2022Satellite broadband
ISRO and Hughes Communications India started India's first high-throughput satellite broadband service.
- 2023Chandrayaan-3
Vikram landed near the Moon's south pole on 23 August 2023, with the Pragyan rover.
- 2023–24Aditya-L1
India's first Sun mission; launched September 2023, reached its orbit round point L1 in January 2024.
- 2025NISAR
ISRO–NASA Earth-watching radar satellite, launched July 2025 from Sriharikota.
With Chandrayaan-3, India became the first country to land near the Moon's south pole, and the fourth to land softly on the Moon. The landing spot is named Shiv Shakti point. 23 August is now National Space Day.
Gaganyaan is India's planned human spaceflight. Its crew-module re-entry test, CARE, flew in December 2014. In June 2025, Shubhanshu Shukla flew to the International Space Station on the Axiom-4 mission. In October 2024 the government said India's own space station, the Bharatiya Antariksh Station, is planned by 2035. Dates of future missions can change; check current news before the exam.
Traps and practice
Last revision — where the options try to fool you.
- The Sun shines by fusion, not fission and not burning.
- Mercury is closest to the Sun, but Venus is the hottest.
- Venus and Uranus spin east to west.
- Solar eclipse: Moon in the middle. Lunar eclipse: Earth in the middle.
- A light year is a distance, not a time.
- A geostationary satellite takes one day per orbit; it is not truly still.
- VSSC is in Thiruvananthapuram; ISRO HQ is in Bengaluru.
- NISAR watches Earth; Aditya-L1 watches the Sun.
Why can an astronaut not drink with a straw on the Moon?
Show answer
Sucking lowers the pressure inside the straw, and air pressure outside pushes the drink up. The Moon has no air, so nothing pushes the drink up.
- Sun's energy
- Nuclear fusion
- Spins east to west
- Venus, Uranus
- Our galaxy
- Milky Way
- Geostationary orbit time
- One day
- India's navigation system
- NavIC
- Father of India's space programme
- Vikram Sarabhai
- First Indian satellite
- Aryabhata, 1975
- Chandrayaan-2 launch
- 2019
- Sun: fusion; light reaches us in about 8 minutes
- Largest Jupiter; closest Mercury; hottest Venus
- Solar eclipse on new moon; lunar on full moon
- No air on the Moon: no straw, no sound
- Geostationary: 24 hours, 36,000 km; IRS: land, water, crops
- Aryabhata 1975; APPLE 1981; Chandrayaan-2 2019; Chandrayaan-3 2023
- NISAR 2025 (Earth); Bharatiya Antariksh Station target 2035