--- title: "Why is summer hot?" subtitle: "Year 7 Earth and space · The Earth and the sun · Lesson 2" --- # Why is summer hot? **Name:** {{field-24}} **Date:** {{field-15}} **Class:** {{field-15}} > **Key question:** On 4 January the Earth is at its closest to the sun all year, five million kilometres closer than in July. That day it's summer in Canberra and winter in London. :::teacher-note **In one sentence:** Students explain seasons by the Earth's axial tilt, link tilt to the height of the noon sun and day length, and use opposite hemispheres and the distance data to reject the distance explanation (AC9S7U03, node 4, a hinge node). **Students should be able to say:** I can explain that seasons are caused by the tilt, not distance from the sun. I can link the tilt to the height of the noon sun and the length of the day. I can explain why the two hemispheres have opposite seasons. **Width:** the unmarked parts are the floor every student does (Engage, Explore, Explain, Evaluate). Typical and Wider sections add contexts, not difficulty. Students work in the online tutorial alongside this sheet. ::: ## Engage :::keep-together **Why is it hotter in Canberra in December than in June?** ☐ The Earth is closer to the sun in December ☐ There are fewer clouds in December ☐ The sun gives out more heat in December ☐ The Earth's tilt makes the Southern Hemisphere lean towards the sun in December My prediction, and why: {{lines-3}} ::: :::teacher-note **What happens:** The tilt. In December the Southern Hemisphere leans towards the sun: the noon sun is high and the days are long. The Earth is in fact closest to the sun in early January, but that changes the sunlight by only about 7%. ::: ## Explore Try it on the board in the tutorial. Was your prediction right? What was different? {{lines-2}} ## Explain: tilt, not distance :::keep-together ### Distance **In late December, when it's summer in Canberra, how far is the Earth from the sun compared with late June?** ☐ About 5 million km closer ☐ Twice as close ☐ The same distance ☐ About 5 million km farther ::: :::teacher-note **Answer:** About 5 million km closer ::: :::keep-together ### A test of distance **If distance caused seasons, what would be true?** ☐ Both hemispheres would have summer at the same time ☐ Australia would have summer in December ☐ Nothing would change ☐ Seasons would be opposite in the two hemispheres ::: :::teacher-note **Answer:** Both hemispheres would have summer at the same time ::: :::keep-together ### Summer and winter **Which go with Canberra's summer, and which with its winter?** Groups: Summer, Winter - Southern Hemisphere leans towards the sun: {{field-15}} - Noon sun high in the sky: {{field-15}} - About 9½ hours of daylight: {{field-15}} - Sunlight hits the ground at a low angle, spread over a bigger area: {{field-15}} - About 14½ hours of daylight: {{field-15}} ::: :::teacher-note **Answer:** Southern Hemisphere leans towards the sun → Summer; Noon sun high in the sky → Summer; About 9½ hours of daylight → Winter; Sunlight hits the ground at a low angle, spread over a bigger area → Winter; About 14½ hours of daylight → Summer ::: ## Mix it up :::keep-together **Looking back at the Earth's spin and orbit: as the Earth goes round the sun, what does its tilted axis do?** ☐ It keeps pointing the same way in space ☐ It stands straight up ☐ It flips over halfway through the year ☐ It always leans towards the sun ::: :::teacher-note **Answer:** It keeps pointing the same way in space The axis keeps pointing the same way in space. That is why each hemisphere leans towards the sun for half the year. ::: ## the other hemisphere :::keep-together ### Why opposite **On 22 June, London has about 16½ hours of daylight and Canberra about 9½. Why?** ☐ London is nearer the equator ☐ The sun is bigger in London ☐ London is closer to the sun ☐ The Northern Hemisphere leans towards the sun in June, and the Southern Hemisphere leans away ::: :::teacher-note **Answer:** The Northern Hemisphere leans towards the sun in June, and the Southern Hemisphere leans away ::: :::wider ## Elaborate: no tilt :::keep-together ### Seasons without tilt **With no tilt, what happens to Canberra's seasons?** ☐ They disappear: about 12 hours of daylight and the same noon sun all year ☐ Nothing changes ☐ They swap ☐ They get stronger ::: :::teacher-note **Answer:** They disappear: about 12 hours of daylight and the same noon sun all year ::: :::keep-together ### Six seasons **In Kakadu, Bininj people recognise six seasons, marked by changes in rain, wind, plants and animals, rather than four. Why can both systems be useful?** ☐ The six seasons are caused by a different tilt ☐ The tilt model explains why the year changes; a six-season calendar describes the changes people actually observe in that place ☐ Kakadu has no seasons ☐ Only the four-season model is science ::: :::teacher-note **Answer:** The tilt model explains why the year changes; a six-season calendar describes the changes people actually observe in that place ::: ::: ## Evaluate: look back Write one sentence: "At first I thought… Now I think… because…" **Revision summary** - Seasons are caused by the Earth's **tilt**, not its distance from the sun (we are closest in January). - Leaning **towards** the sun: the noon sun is **higher** (light concentrated on a smaller area) and days are **longer**: summer. - The two hemispheres have **opposite** seasons. Near the equator the changes are small. ## Exit ticket :::keep-together **Explain why Canberra is hotter in December than in June.** {{lines-3}} ::: :::teacher-note **Answer:** In December the Southern Hemisphere leans towards the sun (the tilt), so the noon sun is higher, concentrating the light, and days are longer. It isn't distance: the Earth is actually slightly closer to the sun in January. :::