Science notes, unit 9

Phases of the Moon and constellations

Textbook Science Year 5 (DLP), pages 199–216

What this chapter covers

You can explain that the Moon does not give out its own light but reflects light from the Sun (9.1.1)
You can describe the rotation and revolution of the Moon, including the time taken and the direction (9.1.2)
You can name the phases of the Moon and say what we see in each phase (9.1.3)
You can use the lunar calendar to link dates with the phases of the Moon (9.1.3)
You can explain with a simulation why the phases of the Moon happen (9.1.4)
You can name some constellations and describe their patterns (9.2.1)
You can explain how constellations are used to show direction and to indicate seasons (9.2.2)
You can build a model of a constellation (9.2.3)

Four circles showing star patterns: the Big Dipper in the northern hemisphere, Orion in the middle, the Southern Cross and the Scorpion in the southern hemisphere — The shape of the Moon changes from night to night, and the stars make patterns in the sky. Why? (Textbook pp. 199, 209)

9.1The Moon

The moonlight

The Moon looks bright at night. Does it make its own light, like the Sun?

The Moon does not give out its own light. It reflects (bounces back) the light from the Sun.

Remember the experiment on the reflection of light. A mirror shines because it reflects the light from the torch. The mirror stands for the Moon. The torch stands for the Sun.

The Moon is not a source of light. The Sun is a source of light. We see the Moon only because sunlight falls on it and bounces to our eyes.

The Moon rotates and revolves

The Earth rotates on its axis and revolves around the Sun at the same time. The Moon makes two movements too.

Movement	What it means	Time for one complete turn	Direction
Rotation	The Moon spins on its own axis.	27 days	Anticlockwise
Revolution	The Moon moves around the Earth.	27 days	Anticlockwise

The Earth in the middle with an oval orbit. A small Moon on the orbit has an arrow showing its spin. Both labels say 27 and one third days. — The rotation period and the revolution period of the Moon are the same. (Textbook p. 202)

Picture: Science Year 5 (DLP) textbook, p. 202.

Rotation time = revolution time = 27 days (the picture above shows the exact value, 27⅓ days). So the same surface of the Moon always faces the Earth. That is why the Moon looks as if it does not rotate.

Try it: hold a balloon with a card stuck on one side. Walk around a globe with the card always facing the globe. You turn the balloon once while you go once around. (Textbook p. 203)

1. What are the two movements of the Moon?
2. Why do we always see the same surface of the Moon?

Show answerHide answer

1. It rotates on its axis and revolves around the Earth. Both are anticlockwise and take 27 days.
2. The Moon takes the same time to rotate once and to revolve once around the Earth, so the same surface always faces the Earth.

9.2Phases of the Moon

The Moon revolves around the Earth, so its position changes with time. Half of the Moon is always lit by the Sun. But from the Earth we see different parts of the lit half on different nights.

The different shapes of the Moon that we see are called the phases of the Moon.

The Sun on the left, the Earth in the middle, and the Moon at eight positions numbered 1 to 8 going anticlockwise around the Earth. Position 1 is between the Earth and the Sun. Position 5 is on the far side of the Earth from the Sun. — The Moon at eight positions on its orbit, seen from above. The side facing the Sun is always lit.

Eight Moon shapes in a row: new moon, crescent, half-moon, gibbous, full moon, gibbous, half-moon, crescent — What we see from the Earth at positions 1 to 8.

Position	Phase	What is facing the Earth
1	New moon	The dark side of the Moon. We cannot see the Moon.
2 and 8	Crescent moon	A small part of the lit surface
3 and 7	Half-moon	Half of the lit surface
4 and 6	Gibbous moon	A large part of the lit surface
5	Full moon	The whole lit surface

The Moon takes the same path every month, so the phases come in the same order again and again: new moon, crescent, half-moon, gibbous, full moon, gibbous, half-moon, crescent, new moon.

The shape of the Moon changes because we see different parts of the lit half. The Moon itself does not change shape, and it does not give out light. If the Moon made its own light, we would always see a full circle and there would be no phases.

Simulation with a ball and a lamp

Use a lamp (the Sun) in the middle of a dark room and a polystyrene ball on a pencil (the Moon). Turn your body to the left and look at the ball.

Photographs of a pupil holding a ball in front of a lamp in a dark room, turning to the left, each with a drawing of the shape of the ball he sees, and a sketch sheet of the eight phases — Point the ball at the lamp, then turn through 45°, 90°, 135° and 180° to see the phases. (Textbook p. 207)

Picture: Science Year 5 (DLP) textbook, p. 207.

Ball position	Phase you see
Pointing at the lamp	New moon
Turn 45°	Crescent moon
Turn 90°	Half-moon
Turn 135°	Gibbous moon
Turn 180° (opposite the lamp)	Full moon

Do this activity in a dark room, so that the lamp is the only source of light.

1. Which phase do we see when the dark side of the Moon faces the Earth?
2. Why do the phases of the Moon happen?

Show answerHide answer

1. The new moon. We cannot see it.
2. As the Moon revolves around the Earth, we see different parts of the Moon that are lit by sunlight.

9.3The lunar calendar

The lunar calendar is based on the phases of the Moon. It is also called the Hijra calendar. The first day of each lunar month is when the new moon has fully appeared.

A table matching the phases of the Moon with the dates of the lunar calendar from new moon on the 1st to new moon again on the 29th and 30th — Phases of the Moon and dates of the lunar calendar. (Textbook p. 206)

Picture: Science Year 5 (DLP) textbook, p. 206.

Phase	Dates of the lunar month
New moon	1, 2
Crescent moon	3 to 6
Half-moon	7 to 10
Gibbous moon	11 to 13
Full moon	14 to 16 (the middle of the month)
Gibbous moon	17 to 20
Half-moon	21 to 24
Crescent moon	25 to 28
New moon	29, 30, then 1 again

Worked example

1 Muharam 1442H was on 20 August 2020 (new moon). On which date was 15 Muharam?
15 Muharam is 15 − 1 = 14 days later. 20 August + 14 days = 34 August = 3 September 2020. The Moon was a full moon.

The lunar calendar is also used to find Islamic celebrations. For example, Hari Raya Aidilfitri is on 1 Syawal, when the new moon has appeared.

What is the phase of the Moon on the 20th day of the lunar month? What is the phase two weeks (14 days) after the 8th day?

Show answerHide answer

20th day: gibbous moon (17 to 20).
8 + 14 = 22nd day: half-moon (21 to 24).

9.4Constellations

Long ago, sailors looked at the stars at night. Some stars seem to form patterns. A group of stars with a pattern is a constellation.

A constellation is a group of stars that appears to form a certain pattern in the sky that can be seen at night.

Not every constellation can be seen from every place on the Earth. Some are seen in the northern hemisphere, some in the southern hemisphere, and some in between.

Constellation	Pattern it looks like	Where it is seen
Big Dipper	A water dipper or scoop (7 stars)	Northern hemisphere
Orion	A hunter wearing a belt and holding a weapon	Between the northern and southern hemispheres
Southern Cross	A kite (4 stars). It is the smallest constellation.	Southern hemisphere
Scorpion	A scorpion	Southern hemisphere

Star patterns joined by lines, each with a picture of what it looks like: a scoop, a hunter, a kite and a scorpion — If you join the stars with lines, you see the patterns. (Textbook p. 210)

Picture: Science Year 5 (DLP) textbook, p. 210.

Did you know? The Big Dipper is part of a bigger constellation called Ursa Major, or the Great Bear.

Which constellation looks like a kite? In which hemisphere can it be seen?

Show answerHide answer

The Southern Cross. It is seen in the southern hemisphere.

9.5Uses of constellations

Constellations help humans to find certain stars. The patterns tell us direction and the time of the year.

To show direction

Travellers and sailors used constellations like a compass.

The Big Dipper with an arrow pointing north and the Southern Cross with an arrow pointing south — The Big Dipper points to the north. The Southern Cross points to the south. (Textbook p. 211)

Picture: Science Year 5 (DLP) textbook, p. 211.

To indicate seasons

Before calendars were invented, farmers in places with four seasons in the northern hemisphere looked at constellations to plan their work.

Constellation	It tells the farmer
Big Dipper	The start of the planting season
Orion	The start of winter
Scorpion	The start of the harvesting season

Do not mix up the two jobs. The Big Dipper and the Southern Cross show direction (north and south). To tell the season, farmers used the Big Dipper (planting), Orion (winter) and the Scorpion (harvest).

Make a model

You can make a model of a constellation with seven small balls of modelling clay and skewer sticks joined to look like the Big Dipper. Use the same way to make Orion, the Southern Cross and the Scorpion. Be careful when you cut the skewer sticks. (Textbook p. 213)

Name two uses of constellations.

Show answerHide answer

To show direction, and to indicate seasons.

Summary

Topic	Remember
Moonlight	The Moon reflects the light of the Sun. It does not make its own light.
Movements	The Moon rotates on its axis and revolves around the Earth. Each takes 27 days and goes anticlockwise.
Phases	New moon, crescent, half-moon, gibbous, full moon, gibbous, half-moon, crescent. They happen because we see different parts of the lit half as the Moon revolves around the Earth.
Lunar calendar	Also called the Hijra calendar. The month starts at the new moon. The full moon is in the middle of the month.
Constellations	A group of stars that forms a pattern. Big Dipper, Orion, Southern Cross, Scorpion.
Uses	To show direction (Big Dipper: north, Southern Cross: south) and to indicate seasons.