FORM 2 CHAPTER 12 SOLAR SYSTEM

CHAPTER 12

SOLAR SYSTEM

12.1 SOLAR SYSTEM

Learning outcome :
12.1.1 Compare distances between the Sun and

the planets in the Solar System using
astronomical units (A.U) and light years(ly).

12.1 SOLAR SYSTEM

• The distance of planets in the solar system from the
Sun is measured by :
(i) Astronomical Unit (A.U.)

(ii) Light years (ly)

(*Not km as the distance is very large!)

Comparison of Planet Distances in the Solar System from the Sun

i) Astronomical Unit (A.U.)
Astronomical unit (A.U.) is the average distance

between the Earth and the Sun, which is
approximately 150 million kilometres.

ii) Light years (ly)

Light years refers to the distance travelled by light

in one year. Light moves at a velocity of 300 000 km
every second.

Therefore, light can move as far as 9.5 x 1012 km in a
year.

1 light year = 9.5 x 1012 km

1 A.U. = 1.5 x 108 km
1 light year = 9.5 x 1012 km



Converting Units between AU, ly and km



Textbook page 253

Planet in the Solar System

• A planet is a massive sphere-shaped body that
orbits a star (Sun).

• The planet does not illuminate light like the stars
but can reflect light because the planet is an
opaque object.









Mercury

• The closest planet to the sun.
• The smallest planet in the solar system. Mercury’s diameter is
40% s Earth's diameter.
• The sky in Mercury is always appears dark because it does not
have a layer of atmosphere to scattered the sunlight.
• The temperature on its surface during the day is very high. It is
approximately 480 C while the temperature at night is extremely
cold, approximately -170C.

Venus

Description
• The second closest planet to the Sun.

• Venus has a layer of atmosphere with a high content of carbon dioxide.
Therefore, it is also known as the green house‘s planet. The temperature
on its surface approximately 460°C because of the high content of
carbon dioxide.

• The rotation of this planet is from east to west, unlike the Earth's. This
means that the Sun rises in the west.

• According to astronomers, Venus is the Earth's twin' because its age,
mass and volume is the same as the Earth's.

Earth

• The third planet in the solar system.

• The fifth largest planet in the solar system.

• The Earth is one of the planets in the universe inhabited by living
things.

• The Earth is surrounded by a layer of atmosphere made up of
nitrogen gas, oxygen, carbon dioxide, argon and water vapour.

• 71% of the surface of the Earth is covered with water and 29% is
covered with land.

Mars

• Fourth planet from the Sun.
• Mars also known as the Red planet.
• Mars has two moon, they are Phobos and Demos.
• Its surface is covered with reddish sand dust.
• It has a thin atmosphere and an extremely high

content of carbon dioxide at 96%.

Jupiter

• Fifth planet from the Sun.
• The largest planet in the solar system.
• It has 67 moons that orbit it and the largest moon

is Ganymede.

Saturn

• Sixth planet from the Sun.

• Second largest planet after Jupiter.

• Saturn is made up of gases and is classified as a gas
giant planet.

• It has ring, made up of ice with small amount of
rocky material and dust.

Uranus

• Seventh planet from the Sun.
• Third largest planet in solar system.
• It is made up of ice element and rocks.
• It has a ring like Saturn but in is thinner and darker.
• It has 27 moons orbiting the planet.

Neptune

• Eight planet from the solar system.

• Methane gives the blue colour to Neptune.

• Takes the longest time to orbit the Sun that is 165 years
(Earth time).

• Being the farthest in the solar system, the temperature
on its surface is extremely cold.

(-201 ˚C)

Relationship between Temperature of
a planet and the Sun (pg258)

Theoretically: nearer to the Sun, hotter. BUT NOT!!!

Factors (atmosphere, CO₂, pressure, gravity) affect the
temperature.

• Planet that do not have atmosphere :
MERCURY
Facing Sun : extremely hot (427 °C)
Dark side : extremely cold (-173 °C)

• Planet that have atmosphere :
(i) Earth:
Clouds reflects sunlight,
atmosphere traps heat, which cause greenhouse

effect.

(ii) Venus :
Very high CO₂ to trap heat, hottest planet =457°C

(iii) Mars :
Even though high CO₂, but surface pressure very

low, -143°C to 35°C.

• For gas giant planets :

Jupiter
Saturn
Uranus
Neptune

Very little sunlight, very cold.

Relationship between Density and
Gravitational force of Planets (pg259)

Higher mass & density,
higher gravitational force.

Relationship between Distance, Time
and speed (pg259)

The further the planet is from the Sun,
the more time it needs to orbit the Sun.

Rotational direction of Planets

• All planets rotates from west to east
(counter-clockwise) except

• Venus and Uranus from east to west

(clock-wise) and Uranus rotates
on its side.

Rotational direction of Planets

What are natural satellites?

• Natural satellites are objects that orbit around
planets on their own orbit.

• The moon is the natural satellite of the Earth.

Hypothetical (假设性) Situation

• What if rotation of Earth stop?

One side of Earth is always day, another side of Earth is
always night.

Part of Earth that faces Sun will become desert
There will be no life on the side of Earth that does not

receive sunlight.
Change of high and low tides.

EARTH AS A PLANET FOR LIFE

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