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SavannahYear 8
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ScienceYear 9 Science: inheritance, energetics, climate, magnetism and space30 min★★★ difficulty

Seasons, day length and distances in space

Summer is not the time when Earth is closest to the Sun. The real explanation is a 23.5° tilt, and it also explains why daylight stretches and shrinks across the year.

Lesson overview

What you'll learn in this lesson

Understand the seasons and the Earth's tilt, day length at different times of year, and the light year as a unit of astronomical distance

Key learning points

  • • The tilt, not the distance
  • • Intensity of sunlight
  • • Day length across the year
  • • Measuring distance in light years

This lesson at a glance

  • 30 minutes
  • 19 parts to scroll through
  • 4 quick checks
  • Marked quiz at the end
  • Gentle pace: short sittings with pauses

Words to know

seasonslengthastronomicaldistanceintensity

Scroll down — the lesson carries on below

Part 1 of 19 · Discover5%
1

Watch & discover

Part 1 of 19

Watch first

Seasons, day length and distances in space

An English teaching video on this topic from LearnScienceWithB. Watch it, then scroll down for the lesson.

In a nutshell

Understand the seasons and the Earth's tilt, day length at different times of year, and the light year as a unit of astronomical distance

2

What you already know

Part 2 of 19

Before we start

What you already know

You should already know that Earth orbits the Sun and rotates once a day.

3

Key words

Part 3 of 19

Key words

Words you'll need today

Axial tilt
The 23.5° lean of Earth's axis relative to its orbit.
Solstice
The longest or shortest day of the year.
Equinox
When day and night are close to equal length.
Light year
The distance light travels in one year.
4

Learning cycle

Part 4 of 19

Learning cycle 1 of 2

Why seasons happen

A short piece of teaching, then a check to make sure it has landed.

5

Explore the idea

Part 5 of 19

Learn

The tilt, not the distance

Earth's axis leans about 23.5° and keeps pointing the same way as Earth orbits. For half the year the northern hemisphere tilts towards the Sun and for half it tilts away. Earth is actually slightly closer to the Sun in January, which is decisive evidence that distance is not the cause of the seasons.

6

Explore the idea

Part 6 of 19

Learn

Intensity of sunlight

When a hemisphere tilts towards the Sun, sunlight strikes it more directly, so the same energy is concentrated on a smaller area and heats it more. Tilted away, the same beam is spread over a larger area and passes through more atmosphere. Concentration of energy per square metre is the mechanism behind summer and winter.

7

Quick check

Part 7 of 19

Quick check

Seasons are caused by...

8

Quick check

Part 8 of 19

Quick check

At an equinox...

9

Reset break

Part 9 of 19

Pause

That's sitting 1 of 2 done

Stretch, get a drink, look out of the window. There is no timer and nothing is counting down — your place is saved, so you can come back in five minutes or tomorrow.

Stop here for now
10

Learning cycle

Part 10 of 19

Learning cycle 2 of 2

Day length and cosmic distances

A short piece of teaching, then a check to make sure it has landed.

11

Explore the idea

Part 11 of 19

Learn

Day length across the year

The tilt also changes how much of each rotation a place spends in sunlight. Near the June solstice the northern hemisphere has its longest day; near the December solstice its shortest. At the equinoxes day and night are close to equal everywhere. Inside the Arctic Circle the effect is extreme enough to give continuous daylight or darkness.

12

Explore the idea

Part 12 of 19

Learn

Measuring distance in light years

Space distances are too large for kilometres to be useful, so astronomers use the light year: the distance light travels in a year, about 9.5 trillion kilometres. It measures distance, not time. Because light takes time to arrive, looking at a star four light years away means seeing it as it was four years ago — telescopes look backwards in time.

13

Quick check

Part 13 of 19

Quick check

A light year measures...

14

Quick check

Part 14 of 19

Quick check

Sunlight in winter feels weaker because it is...

15

Common mix-ups

Part 15 of 19

Common mix-ups

Things people often get wrong

  • People often think summer happens because Earth is closer to the Sun. It is caused by the tilt.
  • People often think a light year is a length of time. It is a distance.
16

Challenge round

Part 16 of 19

Game · Sort it

Which of these are true?

Drag each card into the right column. Tap a card first if dragging is fiddly.

True

Not true

17

Challenge round

Part 17 of 19

Game · Fill the gaps

Finish the sentences

Choose the word that belongs in each gap.

Earth is actually slightly closer to the Sun in January, which is decisive evidence that distance is not the cause of the ____.

Space distances are too large for kilometres to be useful, so astronomers use the light year: the ____ light travels in a year, about 9.5 trillion kilometres.

18

Mastery quiz

Part 18 of 19

Marked quiz

End of lesson quiz: Seasons, day length and distances in space

6 questions, marked with the reasoning shown. No timer.

  1. 1. Earth's axis is tilted at about...

  2. 2. The longest day in the northern hemisphere occurs near the...

  3. 3. Inside the Arctic Circle in midsummer there can be...

  4. 4. A star 10 light years away is seen as it was...

  5. 5. Earth is closest to the Sun in...

  6. 6. Light travels roughly...

19

Lesson round-up

Part 19 of 19

Lesson round-up

Ready when you are

Quiz score

Not sat

Games

Not played

Points this lesson

0

Best run

0 in a row

Luna: 0 out of 4 on the practice checks. Only if you feel up to it — one more?

Ask Luna

Do the work

Your written work for this lesson

This is the part you'd do in your book at school. Pick the pieces below, write here or on paper, and photograph anything you draw or work out.

Case study

Why the school greenhouse failed

A science club grew tomato plants in the school greenhouse. In June the plants grew well: leaves were dark green and the fruit set quickly. In July the club went away for two weeks and left the greenhouse door shut. When they came back, the leaves were curled and pale and most of the fruit had dropped.

The club had a data logger inside. It showed the temperature reached 46 °C on several afternoons and the soil moisture fell close to zero. The club knew photosynthesis needs light, water and carbon dioxide, and that enzymes in a plant work best in a narrow range of temperature. Above that range the enzymes stop working properly.

The club repeated the summer with the door propped open and a water bottle drip on each pot. Temperature peaked at 31 °C and the plants survived.

Written for Good Learning Co.

Reading questions

  1. Name the variable the club changed the second time, and one variable they kept the same.
  2. Explain, using the words photosynthesis and enzymes, why the plants were damaged in July.
  3. Write a conclusion for the club's report, saying how far the evidence supports it.

  • Method and results

    Writing

    Write the aim, what you changed, what you measured and what you kept the same, then record your results in a table.

    1 page + results table

  • Conclusion

    Writing

    Explain what your results show and why, using the scientific words from the lesson. Say how you know you can trust them.

    6–8 sentences

  • Labelled diagram

    Diagram

    Draw the apparatus or the process in pencil, label it fully, and photograph it.

    1 labelled diagram

  • Reading and notes

    Reading

    Read the lesson text again and write the key ideas in your own words.

    Half a page of notes

Saved as you type.

Part 1 of 19 · Watch & discover

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