The Solar System
Astronomy Study Notes | 5 November 2026
1. Solar System
The Solar System includes the Sun and objects held by its gravity: eight planets, dwarf planets, moons, asteroids, comets,
and meteoroids.
2. The Sun
The Sun is a star at the centre of the Solar System. It produces energy through nuclear fusion, mainly converting hydrogen
into helium. Its gravity keeps planets in orbit.
3. Eight Planets
In order from the Sun: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune. The first four are rocky planets.
Jupiter and Saturn are gas giants; Uranus and Neptune are ice giants.
4. Planet Facts
Mercury is closest to the Sun. Venus has a very hot surface. Earth has abundant surface liquid water. Mars looks reddish.
Jupiter is the largest planet. Saturn has prominent rings. Uranus has an extreme axial tilt. Neptune is a distant ice giant.
5. Dwarf Planets
Dwarf planets orbit the Sun and are nearly round, but have not cleared their orbital neighbourhood. Pluto, Ceres, Eris,
Haumea, and Makemake are recognised examples.
6. Moons, Asteroids, and Comets
Moons are natural satellites. Many asteroids orbit in the belt between Mars and Jupiter. Comets contain ice, dust, and rocky
material; near the Sun they can develop a coma and tail.
7. Rotation and Revolution
Rotation is an object's spin on its axis and relates to the length of a day. Revolution is one complete orbit around another
object; Earth's revolution around the Sun defines a year.
8. Earth and Life
Earth orbits in the Sun's habitable zone, where surface liquid water can exist. Liquid water, the atmosphere, and other
conditions help make Earth suitable for life as we know it.
9. Space Exploration
Telescopes, orbiters, landers, and robotic spacecraft help scientists study planets and smaller bodies. They collect images
and measurements about the Solar System's history and composition.
10. Key Terms
Orbit: Path around another object. Rotation: Spin on an axis. Revolution: One complete orbit. Asteroid: Small rocky or
metallic body orbiting the Sun. Comet: Icy body that may form a tail near the Sun. Dwarf planet: Nearly round object orbiting
the Sun that has not cleared its orbital neighbourhood.
11. Short Q&A;
Q1. What is at the centre? The Sun.
Q2. How many planets are there? Eight.
Q3. Which is the largest planet? Jupiter.
Q4. Where is the main asteroid belt? Between Mars and Jupiter.
Q5. Rotation vs revolution? Rotation is spinning; revolution is orbiting.
12. MCQs
1. Closest planet to the Sun? A) Earth B) Mercury C) Mars D) Venus
2. Largest planet? A) Saturn B) Earth C) Jupiter D) Neptune
3. Main asteroid belt? A) Earth-Mars B) Mars-Jupiter C) Jupiter-Saturn D) Uranus-Neptune
Astronomy Study Notes | 5 November 2026
1. Solar System
The Solar System includes the Sun and objects held by its gravity: eight planets, dwarf planets, moons, asteroids, comets,
and meteoroids.
2. The Sun
The Sun is a star at the centre of the Solar System. It produces energy through nuclear fusion, mainly converting hydrogen
into helium. Its gravity keeps planets in orbit.
3. Eight Planets
In order from the Sun: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune. The first four are rocky planets.
Jupiter and Saturn are gas giants; Uranus and Neptune are ice giants.
4. Planet Facts
Mercury is closest to the Sun. Venus has a very hot surface. Earth has abundant surface liquid water. Mars looks reddish.
Jupiter is the largest planet. Saturn has prominent rings. Uranus has an extreme axial tilt. Neptune is a distant ice giant.
5. Dwarf Planets
Dwarf planets orbit the Sun and are nearly round, but have not cleared their orbital neighbourhood. Pluto, Ceres, Eris,
Haumea, and Makemake are recognised examples.
6. Moons, Asteroids, and Comets
Moons are natural satellites. Many asteroids orbit in the belt between Mars and Jupiter. Comets contain ice, dust, and rocky
material; near the Sun they can develop a coma and tail.
7. Rotation and Revolution
Rotation is an object's spin on its axis and relates to the length of a day. Revolution is one complete orbit around another
object; Earth's revolution around the Sun defines a year.
8. Earth and Life
Earth orbits in the Sun's habitable zone, where surface liquid water can exist. Liquid water, the atmosphere, and other
conditions help make Earth suitable for life as we know it.
9. Space Exploration
Telescopes, orbiters, landers, and robotic spacecraft help scientists study planets and smaller bodies. They collect images
and measurements about the Solar System's history and composition.
10. Key Terms
Orbit: Path around another object. Rotation: Spin on an axis. Revolution: One complete orbit. Asteroid: Small rocky or
metallic body orbiting the Sun. Comet: Icy body that may form a tail near the Sun. Dwarf planet: Nearly round object orbiting
the Sun that has not cleared its orbital neighbourhood.
11. Short Q&A;
Q1. What is at the centre? The Sun.
Q2. How many planets are there? Eight.
Q3. Which is the largest planet? Jupiter.
Q4. Where is the main asteroid belt? Between Mars and Jupiter.
Q5. Rotation vs revolution? Rotation is spinning; revolution is orbiting.
12. MCQs
1. Closest planet to the Sun? A) Earth B) Mercury C) Mars D) Venus
2. Largest planet? A) Saturn B) Earth C) Jupiter D) Neptune
3. Main asteroid belt? A) Earth-Mars B) Mars-Jupiter C) Jupiter-Saturn D) Uranus-Neptune
