Chapter 6 of 7

All 7 chapters
  1. 1Where light comes from, readunderstood
  2. 2Light goes in straight lines, readunderstood
  3. 3How we see, readunderstood
  4. 4Opaque, translucent, transparent, readunderstood
  5. 5Big and small shadows, readunderstood
  6. 6A shadow stick through the day, readunderstood
  7. 7Mirrors and shiny things, readunderstood

S2.6.6 Chapter 6

A shadow stick through the day

Why is my shadow long in the morning and short at midday?

Your guess

Pick one before you read on. It is fine to be wrong.

Your guess

  • You picked A. Read on. At the end, the chapter comes back to your guess.

  • You picked B. Read on. At the end, the chapter comes back to your guess.

  • You picked C. Read on. At the end, the chapter comes back to your guess.

By the end you can

  • Make a shadow stick and mark its shadow every hour
  • Say when the shadow is longest and when it is shortest
  • Explain why the Sun seems to cross the sky

A shadow stick is a stick pushed upright into flat ground. Its shadow moves all day. It can show you where the Sun is.

Draw it first

The shadow of a stick, three times in one day

  1. A stick stands in the ground, labelled stick. East is on the right, as in the stones picture below. In the morning the Sun, labelled morning, is low on the right, and a long shadow lies on the left. At midday the Sun, labelled midday, is high above the stick, and the shadow is a short dark patch at its foot. In the evening the Sun, labelled evening, is low on the left, and a long shadow lies on the right. The shadow is labelled shadow.morningstickshadow

    1 In the morning the Sun is low. The shadow is long.

  2. A stick stands in the ground, labelled stick. East is on the right, as in the stones picture below. In the morning the Sun, labelled morning, is low on the right, and a long shadow lies on the left. At midday the Sun, labelled midday, is high above the stick, and the shadow is a short dark patch at its foot. In the evening the Sun, labelled evening, is low on the left, and a long shadow lies on the right. The shadow is labelled shadow.morningmiddaystickshadow

    2 At midday the Sun is high. The shadow is short.

  3. A stick stands in the ground, labelled stick. East is on the right, as in the stones picture below. In the morning the Sun, labelled morning, is low on the right, and a long shadow lies on the left. At midday the Sun, labelled midday, is high above the stick, and the shadow is a short dark patch at its foot. In the evening the Sun, labelled evening, is low on the left, and a long shadow lies on the right. The shadow is labelled shadow.morningmiddayeveningstickshadow

    3 In the evening the Sun is low again. The shadow is long, on the other side.

The Sun is low in the morning, so the shadow is long. The Sun is high at midday, so the shadow is short. Midday is the middle of the day, when the Sun is highest. The shortest shadow of the day is at midday.

Midday is not always 12 o'clock on a clock. Clocks are set for a whole region. The Sun does not follow your clock. Midday may come an hour or more from 12 on your clock.

See it three ways

As a picture

A stick stands in the ground. The Sun is on the left, halfway up the sky. The shadow on the right is labelled shadow. It is as long as the stick is tall.shadow

In words

The Sun is halfway up the sky. Then the shadow is as long as the stick. A lower Sun makes it longer. A higher Sun makes it shorter.

In symbols

Sun halfway up: shadow 1 stick long. Sun higher: less than 1 stick. Sun lower: more than 1 stick.

Does the Sun move across the sky? It seems to. But it is the Earth that moves. The Earth turns round once a day.

Your home turns toward the Sun, and the Sun seems to rise. Later your home turns away, and the Sun seems to set.

A picture of the Earth seen from far above the North Pole. The Sun, labelled Sun, is on the left and sends light to the Earth, labelled Earth. The side facing the Sun is labelled day. The other side is cross hatched and labelled night. An arrow shows the Earth turning.SunEarthdaynight
The Earth turns round once a day. One half has day. The other half has night.

The Earth turns from west to east. So the Sun rises roughly in the east. It sets roughly in the west.

On two days a year, the Sun rises exactly in the east. On those days it sets exactly in the west. On other days it rises north or south of east. It sets north or south of west.

Try it

Make a shadow stick

You need: a straight stick, as long as your arm, about ten small stones, flat ground in the sun all day, or a pot of sand, a clock or a watch, or someone who knows the hour, a string with a stone tied to one end, paper and a pencil, to write the times.

Be safe: Never look at the Sun. Look only at the shadow on the ground.

  1. Push the stick into the ground. Press the soil round it.
  2. Hold the string next to the stick. They should hang the same way.
  3. Put a stone on the tip of the shadow. Write down the time.
  4. Come back every hour and add a stone. Never touch the stick.
  5. At the end of the day, look down at the stones.

What you will see: The first stones are far from the stick. Then they come closer, and then they go far again. The nearest stone marks midday. The stones make a line. On most days it bends a little. The picture is for a home north of the tropics. South of them, the stones lie south of the stick.

If you cannot try it, this is what happens.
A view from above, with north at the top. A stick, labelled stick, is at the bottom. Nine stones, one for each hour, mark the tip of its shadow. They lie in a line from west, on the left, to east, on the right. The left end is labelled morning, the middle midday and the right end evening. The midday stone is the nearest to the stick. Other labels: north, west, east. This picture is for a home north of the tropics.northmorningmiddayeveningwesteaststick

Now look at where the shadow points. It depends on where your home is.

The tropics are the lands near the middle of the Earth. On a map, find the Tropic of Cancer. Find the Tropic of Capricorn. The tropics lie between them.

North of the tropics, the midday shadow points north. This is true all year.

South of the tropics, the midday shadow points south. This is true all year.

Between the tropics, it changes with the time of year. For part of the year it points north. For part of the year it points south. On one or two days a year, the midday shadow almost vanishes. Then the Sun is almost straight overhead.

Three rows, each seen from above with north at the top and south at the bottom. In the first row, north of the tropics, a small square marks the stick, labelled stick, and a black bar of shadow, labelled shadow, points up to N. In the second row, south of the tropics, the bar points down to S. In the third row, between the tropics, dashed bars show the shadow may point either way. Labels: north of the tropics, south of the tropics, between the tropics, N, S, stick, shadow.north of the tropicsNSstickshadowsouth of the tropicsNSbetween the tropicsNS
The midday shadow, seen from above. Dashed: it changes with the time of year.

To find north, face the place where the Sun comes up. Do not look at the Sun itself. North is on your left. This is roughly right.

Look down on your stones from above. Clockwise is the way the hands of a clock turn. North of the tropics, the shadow tip moves clockwise. South of the tropics, it moves the other way. Between the tropics, it depends on the time of year.

A wrong idea many people have

The shadow is shortest when the clock says 12.

Why it feels right: People call 12 o'clock midday. So the Sun must be highest then.

The test that breaks it: Mark the tip every 15 minutes, for a few hours around 12. Find the shortest shadow. Then look at the clock.

What is true: The shortest shadow is at midday by the Sun. On a clock it can be an hour or more from 12.

Key words

shadow stick
a stick pushed upright into the ground, to study its shadow.
midday
the middle of the day, when the Sun is highest.
tropics
the lands near the middle of the Earth, between two map lines.
clockwise
the way the hands of a clock turn.

Back to your guess

The answer is B: The Sun is low in the morning and high at midday.

The Sun is low in the morning, so the shadow is long. At midday the Sun is high, so the shadow is short.

Check yourself

Try each one before you look. A wrong answer tells you where to go next.

  1. The shadow of this stick is long. Where is the Sun?

    A stick stands in the ground. The Sun, labelled Sun, is on the left, low in the sky. A long shadow lies on the right of the stick, labelled shadow.Sunshadow
    Tap your answer.

    1. Not this one. A high Sun makes a short shadow. Look at where the Sun is in the picture. Try another.

    2. Not this one. Then the shadow would be a small pool at its foot. Try another.

    3. Yes, that is right. A low Sun makes a long shadow. A high Sun makes a short one.

    See the answer

    Low in the sky

    A low Sun makes a long shadow. A high Sun makes a short one.

    • If you chose A: A high Sun makes a short shadow. Look at where the Sun is in the picture.
    • If you chose B: Then the shadow would be a small pool at its foot.

  2. Mei lives south of the tropics. At midday, which way does her stick shadow point?

    Tap your answer.

    1. Not this one. North of the tropics, the midday shadow points north. Mei lives south of them. Try another.

    2. Not this one. Mei lives south of the tropics. Her midday Sun is to the north, so the shadow points south. Try another.

    3. Not this one. That happens between the tropics. Mei lives south of them. Try another.

    4. Yes, that is right. South of the tropics, the Sun is north of you at midday. So the shadow points south.

    See the answer

    South

    South of the tropics, the Sun is north of you at midday. So the shadow points south.

    • If you chose A: North of the tropics, the midday shadow points north. Mei lives south of them.
    • If you chose B: Mei lives south of the tropics. Her midday Sun is to the north, so the shadow points south.
    • If you chose C: That happens between the tropics. Mei lives south of them.

  3. Why does the Sun seem to move across the sky?

    Tap your answer.

    1. Yes, that is right. The Earth turns round once a day. Your home turns toward the Sun, and then away.

    2. Not this one. It looks that way. But it is the Earth that turns. Try another.

    3. Not this one. Clouds do not move the Sun. The Earth turns, so the Sun seems to move. Try another.

    See the answer

    The Earth turns.

    The Earth turns round once a day. Your home turns toward the Sun, and then away.

    • If you chose B: It looks that way. But it is the Earth that turns.
    • If you chose C: Clouds do not move the Sun. The Earth turns, so the Sun seems to move.

  4. Kofi's clock says 12. Is his shadow sure to be the shortest now?

    Tap your answer.

    1. Not this one. Clocks are set for a whole region. Midday by the Sun can be an hour or more from 12. Try another.

    2. Not this one. A right clock still keeps the time of a whole region. The Sun does not follow it. Try another.

    3. Yes, that is right. The Sun does not follow the clock. The shortest shadow is at midday by the Sun.

    See the answer

    No. It may be shortest an hour or more from 12.

    The Sun does not follow the clock. The shortest shadow is at midday by the Sun.

    • If you chose A: Clocks are set for a whole region. Midday by the Sun can be an hour or more from 12.
    • If you chose B: A right clock still keeps the time of a whole region. The Sun does not follow it.

  5. From an earlier chapter

    Why does a stick make a shadow in the sun?

    Tap your answer.

    1. Yes, that is right. A stick is opaque. Light goes in straight lines, so the stick blocks it.

    2. Not this one. A shadow is not made by the stick. It is a place light cannot reach. Go to S2.6.4. Try another.

    3. Not this one. Light goes in straight lines. It cannot bend round a stick. Go to S2.6.2. Try another.

    See the answer

    Light cannot go through the stick.

    A stick is opaque. Light goes in straight lines, so the stick blocks it.

    • If you chose B: A shadow is not made by the stick. It is a place light cannot reach. Go to S2.6.4.
    • If you chose C: Light goes in straight lines. It cannot bend round a stick. Go to S2.6.2.

  6. You mark the shadow tip every hour. Which stone is the nearest to the stick?

    See the answer

    The stone at midday, when the Sun is highest.

    A high Sun makes the shortest shadow. So the stone for midday is nearest.

  7. How can you find the Sun with no risk to your eyes?

    Tap your answer.

    1. Not this one. Dark glass does not make the Sun safe to look at. Never look at the Sun. Try another.

    2. Not this one. A mirror sends the Sun's light into your eye. That can hurt as much. Try another.

    3. Not this one. Even one second can hurt your eyes. Never look at the Sun. Try another.

    4. Yes, that is right. The shadow points away from the Sun. Its length shows how high the Sun is. You look at the ground, not at the Sun.

    See the answer

    Look at the shadow of a stick

    The shadow points away from the Sun. Its length shows how high the Sun is. You look at the ground, not at the Sun.

    • If you chose A: Dark glass does not make the Sun safe to look at. Never look at the Sun.
    • If you chose B: A mirror sends the Sun's light into your eye. That can hurt as much.
    • If you chose C: Even one second can hurt your eyes. Never look at the Sun.

  8. Amina's stones are far from the stick, then near, then far. Why?

    A view from above, with north at the top. A stick, labelled stick, is at the bottom. Nine stones mark the tip of its shadow, one for each hour. They lie in a line from west, on the left, to east, on the right. The left end is labelled morning, the middle midday and the right end evening. Other labels: north, west, east. This picture is for a home north of the tropics.northmorningmiddayeveningwesteaststick
    Tap your answer.

    1. Not this one. The stick stays the same height. The Sun changes its height in the sky. Try another.

    2. Yes, that is right. A low Sun makes a long shadow. A high Sun makes a short one. The Sun seems to climb and then sink as the Earth turns.

    3. Not this one. The Earth is not nearer the Sun at midday. The Sun looks higher because the Earth turns. Try another.

    See the answer

    The Sun climbs higher, then sinks lower.

    A low Sun makes a long shadow. A high Sun makes a short one. The Sun seems to climb and then sink as the Earth turns.

    • If you chose A: The stick stays the same height. The Sun changes its height in the sky.
    • If you chose C: The Earth is not nearer the Sun at midday. The Sun looks higher because the Earth turns.

Keep it

Copy this into your exercise book.

A shadow stick shows the path of the Sun. The shadow is long when the Sun is low. It is short at midday. The Earth turns, so the Sun seems to move. Never look at the Sun.

Draw: A stick with three Suns and three shadows: long, short, long.

Reading with a child? A short page for the adult: what this chapter teaches and three questions to ask.

No internet tomorrow? Save the whole book as one file (644 KB). It opens on any phone.