Day, Night & Seasons: Rotation and Tilt · Grade 6 Science
Chapter: Earth, Moon, Sun & Space ModelsDay, Night & Seasons: Rotation and Tilt
Learning goals
- I can explain why the angle of sunlight changes how much energy reaches each square metre.
- I can give two pieces of evidence that distance from the Sun does not cause the seasons.
- I can explain why summer days are longer as well as warmer.
Readings for this unit
Before this unit
Read the chapter opening and the named observation or diagram. Clarify one word or unit that blocks understanding. Recall the relevant earlier measurement, matter, or energy idea.
Study the unit across three 35–45-minute class sessions. Use the worked examples after an attempt and the supplied records when actual equipment is not available.
Earth turns once on its axis every 24 hours, which gives day and night, and travels once around the Sun every 365.25 days, which gives the year. Neither of those on its own produces seasons.
Earth's axis is tilted about 23.5 degrees from the perpendicular to its orbit, and it keeps pointing the same way in space all year. For half the year the northern hemisphere leans towards the Sun and for the other half it leans away, while the southern hemisphere does the reverse.
The distance explanation is wrong, and two facts dispose of it. Earth is actually closest to the Sun in early January, at about 147 million km, and furthest in early July, at about 152 million km. And when it is July in Britain it is winter in Australia, which no distance could produce.
Build your understanding
Where this fits
This lesson and the next two deal with what Earth's motion and the Moon's produce in the sky. The energy argument in the third section uses the radiation ideas from chapter 3, and the shadow geometry from the light lesson returns in the eclipses lesson that follows the next one.
Use three flexible 40-45-minute sessions: rotation and day and night; why distance cannot be the cause; the tilt, the angle of sunlight and day length, then the practice set, revision and the exit check. Workshop, review, quiz and exams have separate time.
Part 1 · Turning, and what it looks like from here
Earth turns from west to east, which is why the Sun appears to rise in the east and set in the west, and the apparent movement of everything in the sky is really our own motion. A point on the equator is carried eastward at about 1670 km per hour, which you do not feel because everything around you, including the atmosphere, is moving with you, exactly as you do not feel 900 km per hour in a smooth aircraft.
The evidence that it is Earth turning rather than the sky revolving took a long time to become direct. The decisive demonstration came in 1851, when Leon Foucault hung a heavy pendulum from the dome of the Pantheon in Paris and showed that its swing appeared to rotate slowly through the day. A pendulum swings in a fixed plane, so if the floor beneath it appears to turn, the floor is what is moving. That experiment can be set up in a stairwell and is one of the few ways to detect Earth's rotation from inside a building. There is an older and simpler clue available to anyone who watches the night sky for a few hours. The stars appear to wheel around a single point close to Polaris, completing a full circle in just under 24 hours, and long-exposure photographs record this as concentric arcs. Either every star in the sky is circling us in perfect formation, or we are turning, and the second requires far less explaining.
Pause and explain
How did Foucault's pendulum show that Earth rotates rather than the sky?
Check your reasoning after answering
Because a swinging pendulum keeps swinging in the same plane unless something pushes it sideways. Foucault's pendulum appeared to rotate its swing through the day, and since nothing was pushing it, the only explanation is that the building and the ground beneath it were turning underneath the pendulum.
Part 2 · Why distance cannot be the answer
The distance explanation is the single most common misconception about seasons, and it survives because it sounds sensible: closer should mean hotter. Two observations kill it. First, Earth's orbit is very nearly circular, and the small variation it does have runs the wrong way for the northern hemisphere: we are closest to the Sun at about 147 million km in early January and furthest at about 152 million km in early July, a difference of only about 3 per cent.
Second and more decisively, the seasons in the two hemispheres are opposite. December is midsummer in Sydney and midwinter in London on the same day, at the same distance from the Sun, which no explanation based on distance can accommodate at all. This is a clean example of the test from chapter 1: the distance idea makes a prediction, that both hemispheres should be warm together, and the prediction is plainly false. Any explanation that survives must treat the two hemispheres differently, and tilt is the only candidate that does. It is worth adding that Earth's orbit is far closer to a circle than most diagrams suggest. Textbook pictures draw it as a pronounced ellipse to make the Sun's off-centre position visible, and a drawing to scale would be indistinguishable from a circle to the eye. That exaggerated picture is probably where much of the distance misconception comes from, which is a reminder from chapter 1 that a diagram is a model and can mislead as well as help.
Pause and explain
Why do opposite seasons in the two hemispheres rule out distance as the cause?
Check your reasoning after answering
Because both hemispheres are the same distance from the Sun at any moment. If distance caused the seasons, Sydney and London would be warm together and cold together. They are not: December is midsummer in one and midwinter in the other, so whatever causes seasons must act differently on the two halves of the planet, which tilt does and distance cannot.
Part 3 · The angle is what matters
When sunlight arrives perpendicular to the ground, a beam of a given width lands on the smallest possible area, so the energy per square metre is at its maximum. Tilt the same beam and it spreads over a larger patch, so each square metre receives less. A beam arriving at 30 degrees above the horizon spreads over roughly twice the area that the same beam covers when overhead, halving the energy delivered to each square metre. Sunlight at a low angle also passes through much more atmosphere, so more of it is scattered or absorbed before reaching the ground.
The tilt of 23.5 degrees is what changes that angle through the year. In the hemisphere leaning towards the Sun, the midday Sun climbs higher and its light arrives closer to perpendicular, so the ground receives more energy per square metre and warms. In the hemisphere leaning away, the midday Sun stays low and the same sunlight is spread thin. You can test the idea directly with a torch and a sheet of paper, measuring how the lit patch grows as you tilt the paper, which is the whole of the seasons in one demonstration. Seasons also lag behind the Sun's position by several weeks, and the reason comes from chapter 2. The longest day in the northern hemisphere is around 21 June, and the warmest weeks are usually late July and August, because the ground and especially the oceans take time to warm up, with water needing about 4180 joules per kilogram per degree. The same lag works in reverse in winter, which is why February is often colder than December despite the days lengthening.
Pause and explain
Why does sunlight arriving at a low angle deliver less energy to each square metre?
Check your reasoning after answering
Because the same beam is spread over a larger area. Light arriving perpendicular to the ground concentrates its energy on the smallest possible patch, while a beam arriving at 30 degrees covers roughly twice that area, so each square metre receives about half as much. Low-angle light also travels through more atmosphere, losing more on the way.
Part 4 · Longer days as well
The tilt changes day length at the same time, and the two effects work together rather than separately. In the hemisphere leaning towards the Sun, more than half the line of latitude is in sunlight as Earth turns, so days are longer than nights; in the opposite hemisphere the reverse holds. London gets about 16 hours 40 minutes of daylight in late June and about 7 hours 50 minutes in late December, so midsummer provides more than twice the hours of midwinter as well as stronger sunlight in each of them.
The effect grows with latitude until it becomes absolute. Above the Arctic Circle at 66.5 degrees north, which is simply 90 minus the 23.5 degree tilt, there is at least one day a year when the Sun never sets and one when it never rises. At the North Pole the Sun stays up for about six months and down for six. At the equator, by contrast, day length barely changes at all through the year, which is why tropical regions have wet and dry seasons rather than warm and cold ones. The tilt is not permanently fixed either, although it changes far too slowly to notice. It varies between about 22.1 and 24.5 degrees over roughly 41,000 years, and the orbit's shape and the direction the axis points change on their own long cycles. Those slow variations alter how sunlight is distributed across the seasons and are thought to be the pacemaker of the ice ages recorded in the ice cores from chapter 6.
Pause and explain
Why is the Arctic Circle at 66.5 degrees north rather than at some other latitude?
Check your reasoning after answering
Because it is 90 degrees minus the 23.5 degree axial tilt. That is the latitude at which, on the day the hemisphere leans furthest towards the Sun, the Sun just fails to set, and six months later just fails to rise. A different tilt would place the circle at a different latitude, so the number comes directly from the tilt.
Apply the whole unit · Settle the argument
A student argues that summer happens because Earth is closer to the Sun then. You have the following data: Earth is 147 million km from the Sun in early January and 152 million km in early July; midday Sun height in London is about 62 degrees in June and about 15 degrees in December; London has 16 hours 40 minutes of daylight in June and 7 hours 50 minutes in December; and Sydney's warmest month is January.
Your task
Use the data to refute the distance explanation and give the correct one.
What your response should show
- Names the January perihelion and the opposite southern seasons as the refuting data
- Explains the angle effect in terms of energy per unit area
- Includes day length as a second contributing factor
- Notes that the two effects compound rather than simply adding
Response guidance — after your attempt
Identify which two pieces of data most directly contradict the distance explanation.
Explain how the Sun's midday height changes the energy reaching each square metre.
Combine the angle and the day length into a complete explanation.
Two pieces of data contradict the distance explanation directly. Earth is closest to the Sun in January, which is midwinter in London, so the northern summer happens when Earth is furthest away; and Sydney's warmest month is January, when London's is July, even though both cities are the same distance from the Sun on any given day. No distance-based explanation can produce opposite seasons at the same distance. The real cause is the 23.5 degree tilt. In June the northern hemisphere leans towards the Sun, so the midday Sun reaches 62 degrees above the horizon in London and its light arrives close to perpendicular, concentrating energy on a small area of ground; in December it reaches only 15 degrees, spreading the same beam over roughly four times the area and passing through far more atmosphere on the way. The tilt also lengthens the day, giving 16 hours 40 minutes of that stronger sunlight in June against 7 hours 50 minutes of much weaker sunlight in December. The two effects multiply rather than merely add, which is why the difference between the seasons is so large while Earth's distance from the Sun varies by only about 3 per cent.
Scientific references for this unit
- NASA: what causes the seasons and the role of axial tilt
- National Oceanic and Atmospheric Administration: solar position and day length calculator
- NASA: Earth's orbit, perihelion and aphelion distances
- Smithsonian: Foucault's pendulum and the demonstration of Earth's rotation
Parent / teacher teaching notes
Begin with the literal observation, quantity, or diagram relationship. Ask the learner to explain why the evidence supports the claim, check a relevant unit or boundary, then discuss an alternative. The supplied numbers are illustrative, not real observations. A parent can read aloud and allow a spoken rehearsal before writing. Judge science and evidence rather than political, faith, or family agreement. Use the complete data option whenever an actual procedure is unavailable or unsuitable.
The key idea
Seasons are not caused by Earth's distance from the Sun. They are caused by the 23.5 degree tilt of its axis, which changes both the angle sunlight strikes the ground and how long the Sun is up, and the clearest proof is that the two hemispheres have opposite seasons at the same moment.
Worked examples
Example 1 · A seasonal energy model
- Multiply rate per area by daylight duration.
- Compare angle-related rate and day length.
- Distinguish a simple illumination model from a weather forecast.
Example 2 · Transfer to a different case
- Identify the distinction and conditions in this new case.
- Use the relevant mechanism or quantity; preserve units and the chosen boundary.
- Explain why the answer fits and what further evidence would be needed.
Example 3 · Distinguish an axis and an orbit · a focused example
- State the literal condition or observation in the example.
- Apply the distinction explained in this teaching part.
- Check whether the claim stays within the given evidence.
Avoid these mistakes
- Misleading claim: Day and night are caused by Earth completing an orbit each day.
- Misleading claim: Opposite hemispheric seasons are explained by Earth–Sun distance alone.
- Omitting units, measurement timing, or a model boundary makes the evidence hard to interpret.
- Treating illustrative classroom data as real field measurements or copying a model is not an independent explanation.
Check your understanding
Which motion explains the location’s daily change?
Discuss the answer
Earth’s rotation. One orbit is a different motion associated with the year.
Why keep the tilt direction approximately fixed?
Discuss the answer
That allows each hemisphere’s orientation toward sunlight to change during the orbit and creates the seasonal contrast.
What changes when the same beam is spread farther?
Discuss the answer
Energy received per unit area decreases under this model, even though the total beam amount stays 100.
Why does the hemispheric contrast matter?
Discuss the answer
It challenges the claim that distance alone causes the familiar opposite seasons; orientation and day length provide a better explanation.
Sustained scientific explanation and revision
These activities are scheduled in the parent plan. Save a first response, a correction, and the reason for the change in the science notebook.
Activity 1 · Day, Night & Seasons: Rotation and Tilt · Model and explain
Read One Sky, Several Mechanisms and the linked unit teaching; use its complete supplied case and diagrams.
Your task
For Day, Night & Seasons: Rotation and Tilt, study Parts 3–4 and attempt the worked case: Calculate daily totals and explain the two contributing differences and one limit. Explain the steps before opening the model.
Success criteria
- An accurate scientific claim answering the actual question.
- Relevant evidence or a labeled model with quantities and units when applicable.
- Reasoning that connects evidence with the mechanism rather than only repeats it.
- A specific method, boundary, scale, or alternative-explanation limit.
Hint
Begin with the actual observation, quantity, or diagram relationship. Explain how it bears on the question before making a broad claim.
Response guidance — discuss after your attempt
Summer gives 840 units per area per day and winter 350. Both longer daylight and the larger modeled received rate contribute. These illustrative values explain an energy mechanism, not a guaranteed daily temperature, and real clouds, surface properties, and seasonal response also matter.
Activity 2 · Day, Night & Seasons: Rotation and Tilt · Practice, revise and exit
Read One Sky, Several Mechanisms and the linked unit teaching; use its complete supplied case and diagrams.
Your task
For Day, Night & Seasons: Rotation and Tilt, complete practice questions 1–6 and both choice checks, then answer independently: A location has a cold summer day. Does that reverse Earth’s seasonal geometry? Save a correction explaining one changed claim or method.
Success criteria
- An accurate scientific claim answering the actual question.
- Relevant evidence or a labeled model with quantities and units when applicable.
- Reasoning that connects evidence with the mechanism rather than only repeats it.
- A specific method, boundary, scale, or alternative-explanation limit.
Hint
Begin with the actual observation, quantity, or diagram relationship. Explain how it bears on the question before making a broad claim.
Response guidance — discuss after your attempt
No. Weather varies within seasons. The geometry concerns a broader illumination pattern, not a guarantee that every summer day is warm.
Words to know
- rotation
- A body turning about its axis.
- revolution
- A body’s orbital movement around another body or system.
- evidence
- A relevant observation, measurement, or record used to evaluate a claim.
- system boundary
- The chosen limit specifying what is included and which exchanges cross it.
- uncertainty
- A stated limit in measurement or knowledge, distinct from a careless mistake.
In the real world
Exit check
A location has a cold summer day. Does that reverse Earth’s seasonal geometry?
Check your explanation after answering
No. Weather varies within seasons. The geometry concerns a broader illumination pattern, not a guarantee that every summer day is warm.
Explain your reasoning without notes. If a key idea is missing, revisit the lesson and try again.