Science notes, unit 9

The solar system

Textbook Science Year 3 (DLP), pages 115–126

What this chapter covers

You can name the members of the Solar System and say the planets in order from the Sun (9.1.1)
You can say that planets nearer the Sun are hotter than planets farther away (9.1.2)
You can explain that every planet moves around the Sun in its own path called an orbit (9.1.3)
You can say that a planet farther from the Sun takes longer to go once around the Sun (9.1.4)
You can make a model to show the Solar System (9.1.5)

A family at the National Planetarium watching the Sun and planets on a big dome screen — Langgi and his family visit the National Planetarium in Kuala Lumpur. What do they see on the screen? (Textbook p. 115)

9.1Members of the solar system

Look up at night. You can see the Moon and the stars. Far away in space is our home, the Solar System.

The Solar System is the Sun and everything that moves around it. "Solar" means "of the Sun".

The Solar System has six kinds of members:

Member	What it is
Sun	A very big, very hot star. It is at the centre of the Solar System.
Planets	Eight big round worlds that move around the Sun. Earth is one of them.
Natural satellites	Natural objects that move around a planet. The Moon is Earth's natural satellite.
Asteroids	Big pieces of rock. Most are between Mars and Jupiter.
Meteoroids	Small pieces of rock. They break off when asteroids crash into each other.
Comets	Balls of ice and dust with a long, bright tail.

Natural satellite
The Moon

Asteroid
A big rock

Meteoroids
Small pieces of rock

Comet
Has a bright tail

Pictures: Science Year 3 (DLP) textbook, pp. 116–117.

Did you know? When a meteoroid falls into our sky, it burns and makes a bright line of light. People call it a "shooting star". It is not a star at all!

The eight planets in order

The planets go around the Sun in a fixed order (sequence). Start from the planet nearest the Sun:

The Sun on the left, then Mercury, Venus, Earth, Mars, the asteroids, Jupiter, Saturn, Uranus and Neptune — The planets in order from the Sun. The sizes and distances are not to scale.

Order	Planet	Easy clue
1	Mercury	Nearest the Sun and the smallest
2	Venus	The hottest planet
3	Earth	Our home. It has air, water and living things.
4	Mars	The red planet
5	Jupiter	The biggest planet
6	Saturn	Has big, beautiful rings
7	Uranus	Pale blue-green
8	Neptune	Farthest from the Sun and the coldest

Remember the order with this sentence: My Very Easy Method Just Speeds Up Naming. (Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune)

Did you know? Saturn is not the only planet with rings. Jupiter, Uranus and Neptune have rings too, but they are thin and hard to see. Pluto was once called the 9th planet. Since 2006 it is called a dwarf planet.

The Moon is not a planet. It moves around the Earth, so it is a natural satellite. The Sun is not a planet either. It is a star.

1. Which planet is third from the Sun?
2. Where are most asteroids found?

Show answerHide answer

1. Earth.
2. Between Mars and Jupiter.

9.2Temperature of the planets

Lim's family is having a barbecue in the kampung. Lim stands next to the fire. He is sweating! His friends stand far away. They do not feel hot.

Lim cooking at a barbecue fire; his friends stand farther away at a table — Nearer the fire, it is hotter. (Textbook p. 120)

The Sun is like the fire. The Sun gives heat to the whole Solar System. Temperature tells us how hot or cold something is.

Planets nearer the Sun have a higher temperature (hotter).
Planets farther from the Sun have a lower temperature (colder).

Planets in a row from the Sun with a colour bar from red (hotter, near the Sun) to blue (colder, far away) — The farther from the Sun, the colder the planet. But Venus is different. Read why below.

So Mercury is very hot. Neptune is the coldest planet, because it is the farthest from the Sun.

Venus is the hottest planet, not Mercury! Venus has a thick atmosphere that traps heat. An atmosphere is a layer of gas around a planet. It works like a thick blanket.

A girl explaining that Venus is the hottest planet because of its thick atmosphere — (Textbook p. 121)

Did you know? Venus is about 460 °C. That is hotter than the oven used to bake kuih. Neptune is about −200 °C, much colder than the ice in your freezer.

The Earth is moved to where Uranus is. Can people still live on it? Why?

Show answerHide answer

No. It is too far from the Sun, so it will be too cold for living things.

9.3Orbit of planets

Have you played with a toy car track? The cars go round and round on the same track.

A boy playing with toy cars racing around an oval track — Each car stays on its track. (Textbook p. 122)

Planets are like the cars. Each planet moves around the Sun on its own path. We say the planet revolves around the Sun. Revolve means to move round and round something.

An orbit is the path of a planet around the Sun. It is elliptical (oval, a little like an egg). It is an imaginary path: we cannot see it in space.

The Sun in the middle with eight oval orbit lines around it, and a planet on each line — Every planet has its own orbit around the Sun. (Textbook p. 122)

Planets go around the Sun. The Moon goes around the Earth. Do not mix them up!

Uranus revolves around the ______ in its orbit.

Show answerHide answer

Sun.

9.4Revolution time of the planets

Look at the orbits of the Earth and Mars. Mars is farther from the Sun, so its orbit is longer. Mars needs more time to go once around the Sun.

A tablet showing the Sun, the Earth's orbit and the bigger orbit of Mars — Mars's orbit is longer than the Earth's orbit. (Textbook p. 124)

The revolution time is the time a planet takes to go once all the way around the Sun.
The farther a planet is from the Sun, the longer its revolution time.

The Earth takes one year to go around the Sun once. That is why we have a birthday once a year!

Planet	Time to go once around the Sun
Mercury	About 88 days (shortest)
Venus	About 225 days
Earth	1 year (365 days)
Mars	About 2 years
Jupiter	About 12 years
Saturn	About 29 years
Uranus	About 84 years
Neptune	About 165 years (longest)

Try it in the school field

Tie a rope to a pole. Hold the end and walk around the pole once. Then try a longer rope. With a longer rope, your circle is bigger, so you take more time to go round. Planets are the same!

A pupil walks in a circle around a wooden pole holding a rope while a friend times him — (Textbook p. 125)

Did you know? If you lived on Mercury, you would have a birthday about every 3 months. On Neptune, nobody would live long enough to have even one birthday!

Which planet takes the shortest time to go once around the Sun? Why?

Show answerHide answer

Mercury, because it is nearest the Sun, so its orbit is the shortest (smallest).

9.5Make your own solar system

You can make fun models to show what you learnt.

Balloons of different sizes placed on circles drawn on manila card

Solar System balloons
Big balloon for the Sun. Smaller balloons for the planets, in order.

An orrery made of paper strips joined to a paper cup with the Sun in the middle

Orrery
Strips of different lengths. A longer strip means farther from the Sun.

Pop-up card
Write facts about one planet.

A round lantern made of coloured paper strips with planet facts

Planet lantern
Paper strips with planet facts.

Pictures: Science Year 3 (DLP) textbook, pp. 118–119, 123, 125.

An orrery is a model that shows the positions and movement of the planets around the Sun. In your model, always put the Sun in the centre.

In the orrery, what does the length of each strip show?

Show answerHide answer

The distance of the planet from the Sun.

Summary

The Sun, the eight planets in order, and pictures of a natural satellite, an asteroid, a meteoroid and a comet — (Textbook p. 126)

Topic	Remember
Members	Sun, planets, natural satellites, asteroids, meteoroids and comets. The Sun is at the centre.
Order of planets	Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune
Temperature	Nearer the Sun = hotter. Farther = colder. Venus is the hottest. Neptune is the coldest.
Orbit	Every planet revolves around the Sun in its own oval path called an orbit.
Revolution time	Farther from the Sun = longer time to go once around. Mercury is the shortest. Neptune is the longest.