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Teacher guide: Year 10 Earth and space

The universe from the big bang to today and the evidence that it is expanding, then Earth's energy balance: sunlight absorbed and reflected, energy flowing between the spheres, and the greenhouse effect. Concept tutorials with a timeline of the universe, expanding space, and a live energy-balance model.

Open the student course

Each lesson works two ways. Students can work through the online tutorial at their own pace (it checks their answers and saves their progress in their browser), or you can teach it to the whole class from the slides, then send students into the tutorial for the Modify and Make steps.

Every lesson guide has plain-language notes, the answers to every check, a solution for every task, and slides and a worksheet for Waypoints Prepare. These guide pages are not linked from student pages, but they are not secret either: keep printed Teacher editions for answers you do not want students to find.

The big bang

The big bang model and redshift as evidence for expansion (AC9S10U03).

The big bang in 5 minutes (read before teaching this unit)

The idea in plain words

  • The big bang theory says space, time, matter and energy began about 13.8 billion years ago in an extremely hot, dense state, and the universe has been expanding and cooling ever since. It wasn't an explosion into empty space: space itself expands.
  • Stages: inflation (a tiny fraction of a second); protons and neutrons (a millionth of a second); hydrogen and helium nuclei (3 minutes); atoms, and light set free (380 000 years: the cosmic microwave background); the dark ages; the first stars (about 200 million years); galaxies (about 1 billion years); the sun and Earth (9.2 billion years).
  • Heavier elements (carbon, oxygen, iron) were made later, inside stars and in supernovae.
  • Redshift: light from distant galaxies is shifted to longer (redder) wavelengths, so they are moving away from us. Hubble found that farther galaxies move away faster: what you'd see from any galaxy if space is expanding. Run the expansion backwards and everything was once together.

Where the picture breaks

  • The timeline board spaces the stages evenly; the real times run from a tiny fraction of a second to billions of years.
  • The expanding-space board is 2D and its redshifts are drawn 5 times bigger. Real galaxies also have their own small motions (nearby Andromeda is blueshifted, moving towards us).
  • Strictly, cosmological redshift is space stretching the light on its way, not just a Doppler effect; at Year 10 the Doppler picture is a good model.

Common misconceptions

  • The big bang was an explosion at one point in space, and we are near the centre.
  • Galaxies are flying through space away from a centre (space itself is stretching; there is no centre).
  • The universe started from a tiny speck sitting in empty space.
  • All elements were made in the big bang.

Investigate in class

Optional ideas if you run a practical for this unit: pick one, adapt it to your equipment, or use your own.

  • Do farther galaxies move away faster? A model: dots drawn on a part-inflated balloon, one marked "home". Change: each dot's starting distance from home. Measure: how much that distance grows when the balloon is blown up a bit more. Keep the same: the extra inflation. (Every distance grows by the same factor, so farther dots move further in the same time: Hubble's law. Any dot could be home.)
  • Does stretching space stretch the light? A model: a wave drawn along a wide rubber band. Change: how far the band is stretched. Measure: the wavelength before and after. Keep the same: the band, the drawn wave. (Longer wavelength means redder: redshift.)

Safety and ethics: check for latex allergies before using balloons; hold bands low so a snap doesn't hit eyes.

Earth's energy balance

Sunlight in, energy balance between the spheres, and the greenhouse effect (AC9S10U04).

Earth's energy balance in 5 minutes (read before teaching this unit)

The idea in plain words

  • The sun delivers on average about 340 W/m² to the top of the atmosphere. About 30% is reflected (clouds, ice, bright surfaces): this fraction is the albedo. The rest is absorbed and warms the surface, oceans and air.
  • Earth gives energy back to space as infrared radiation. When energy out equals energy in, Earth is in energy balance and its temperature stays steady. If in exceeds out, Earth warms until the extra outgoing infrared restores balance.
  • Energy moves between the spheres by radiation, conduction and convection (warm air rising, evaporation). The oceans store most of the extra heat and move it around the world.
  • Greenhouse gases (water vapour, CO₂, methane, nitrous oxide) absorb infrared from the surface and send some back down. They slow the energy going out, not the sunlight coming in. Without them Earth's average surface would be about −18 °C instead of about 15 °C (the natural greenhouse effect). Adding more (the enhanced greenhouse effect) creates an imbalance, so Earth warms.

Where the picture breaks

  • The board's model has one atmosphere layer and one surface temperature; real climate has clouds, winds, currents, ice and feedbacks.
  • In the model, sunlight passes straight through the air; really about a fifth is absorbed on the way down.
  • The model reaches balance in a few decades; the real deep ocean takes centuries.

Common misconceptions

  • The greenhouse effect is the ozone hole.
  • Greenhouse gases trap incoming sunlight (they slow outgoing infrared).
  • The greenhouse effect is entirely bad (without it Earth would be frozen).
  • Energy balance means nothing is happening (huge flows in and out are equal).

Investigate in class

Optional ideas if you run a practical for this unit: pick one, adapt it to your equipment, or use your own.

  • Does the colour of a surface change how much it warms? Change: the surface (white card, black card, foil, dark soil). Measure: the temperature rise after 15 minutes under a lamp. Keep the same: the lamp, its distance, the thermometer's position. (A model of albedo: compare ice and ocean.)
  • Does water warm up more slowly than sand? Change: the material (water or dry sand, same mass). Measure: the temperature rise after 15 minutes under a lamp. Keep the same: mass, container, lamp distance. (Why the oceans store so much heat.)
  • Has Australia warmed? Secondary data: the Bureau of Meteorology's annual temperature anomalies for Australia. Change: the decade. Measure: the average anomaly. Keep the same: the data set.

Safety and ethics: heat lamps get hot; keep water away from the lamp and its cord.