The Big Bang and the Universe: a full term of science

Ten ready-to-teach lessons for Year 10 Earth and space sciences. Print this pack and the term is prepared: every lesson comes with a step-by-step plan, the questions to ask, a student worksheet, cut-out cards, a class sheet or exit tickets, an assessment kit and worked answers.

Start here: five minutes to Monday

1. Skim the term at a glance on the next page.
2. Print the lesson you need. Each lesson is three A4 sheets: plan, worksheet, and cards, a class sheet or tickets.
3. Gather the few items under “You need” on the plan. Most come from the classroom or the science prep room.
4. Open the free interactive unit on your board or projector. Every plan tells you which picture to show and when.
5. Teach straight from the plan. Timings, talk prompts, misconceptions and worked answers are all on the one page.

For any Year 10 science teacher

The pack suits a physics or astronomy specialist and a teacher working outside their own subject alike: each plan explains the idea in plain words, lists the misconceptions students bring, and gives worked answers. The big idea of the term: the big bang theory models a universe that began extremely hot and dense 13.8 billion years ago and has been expanding and cooling ever since. It is not an explosion into empty space; space itself stretches. Three separate lines of evidence support it: the redshift of galaxies, which grows with distance; the faint microwave glow left from the hot early universe; and the amounts of hydrogen and helium made in its first minutes.

Two ways to run each lesson

Every lesson works as one 60-minute block, or as two 30-minute sessions; the split point is marked in every plan. Look ahead: Lesson 3 is richer with diffraction glasses and a couple of lamps, and Lesson 6 needs a latex-free balloon for each pair.

Safety and care in one look

Never look at the Sun, with or without diffraction glasses. Gas discharge tubes, if the school has them, run on high voltage and are handled by the teacher only. Balloons in Lesson 6 are latex-free, blown up by hand, and kept away from faces. Most of the data in this pack are example values in the pattern astronomers measure, and every sheet says so.

The term at a glance

One lesson a week for a term. Each lesson stands on the ones before it, so run them in order where you can.

How the sequence builds

Lessons 1 and 2 build a sense of the size and age of the universe, and why looking far away means looking back in time. Lessons 3 to 6 follow the first line of evidence, from the lines in a spectrum to redshift, Hubble’s law and a model of expanding space. Lessons 7 and 8 add the second and third lines, the microwave glow and the light elements. Lesson 9 weighs the evidence against a rival model, and Lesson 10 brings it together.

Curriculum links (Australian Curriculum V9)

The whole term teaches the Science Understanding descriptor AC9S10U03 quoted on the cover. The lessons also work these Science Inquiry and Human Endeavour descriptors:

Assessment in this pack

• Every plan ends with “Answers and look-fors”: what meeting the idea sounds like in a Year 10 voice, with working.
• The assessment sheet near the front has a class observation checklist and a three-level rubric.
• Lesson 10 is the summative pair: the galaxy survey task, plus the “Show what we know” check.

Materials for the whole term

One gathering session covers all ten lessons, and most of it is already in the classroom or the science prep room. Two things are worth doing ahead: find out whether the prep room has diffraction glasses for Lesson 3, and buy latex-free balloons for Lesson 6.

The one-trip list

• From the prep room: diffraction glasses or grating slides, if there are any, and a lamp or two.
• From the classroom: rulers, string, markers, scissors, coloured pencils and calculators.
• From a party shop: round latex-free balloons, one for each pair and a few spares.

Safety and care in one look

• Never look at the Sun, with or without diffraction glasses.
• Gas discharge tubes, if you use them, run on high voltage: the teacher handles them.
• Balloons are latex-free, blown up by hand and kept away from faces.

Assessment without extra work

The term assesses itself. Every lesson plan ends with worked answers and look-fors, and Lesson 10 is the summative pair: the galaxy survey task, in which students turn five measurements of redshift into speeds and distances and explain the evidence for the big bang, and the final check. This sheet is the place to note what you see along the way.

The three levels

Class observation checklist

A tick a lesson is plenty; the Lesson 10 task and check fill the gaps.

Word wall cards

Cut out the cards and build the wall as the words arrive: light-year and galaxy in Lesson 1; universe and big bang theory in Lesson 2; spectrum and spectral lines in Lesson 3; wavelength, redshift and blueshift in Lesson 4; megaparsec, Hubble’s law and Hubble constant in Lesson 5; expansion of space in Lesson 6; cosmic microwave background and kelvin in Lesson 7; nuclear fusion and neutron star in Lesson 8; steady state theory, prediction and evidence in Lesson 9.

Dear families

This term in science, Year 10 studies the big bang theory: how the universe began hot and dense 13.8 billion years ago and has been expanding and cooling ever since, and the evidence that astronomers use to test the theory.

Along the way your student will put the Moon, the Southern Cross and distant galaxies in order of distance, squeeze the history of the universe into one calendar year, read the lines in the spectra of stars, measure redshift, blow up a balloon to model expanding space, and learn why the oldest light in the universe now reaches us as faint microwaves.

Try this at home

• On a clear night away from city lights, find the Southern Cross and the two Pointers. Their light left them years to centuries ago.
• Look at a streetlight through the grooves of an old CD or DVD at an angle: the colours you see are its spectrum.
• Work out the light travel time from the Sun: 150 million km at 300 000 km/s. Is it more or less than ten minutes?
• Ask your student to explain why the big bang was not an explosion in space.

What to ask your scientist

• What is a light-year, and why is it a distance and not a time?
• How do astronomers know that galaxies are moving away from us?
• What is the cosmic microwave background?
• Where did the atoms in your body come from?

A small note on safety: the class never looks at the Sun, with or without the special glasses used to split light into colours, and the balloons in the expanding-space lesson are latex-free.

Warm regards,

The Year 10 science team

Printed from the free seegongsik The Big Bang and the Universe teaching pack · seegongsik.com/au/y10/earth-and-space/AC9S10U03/pack

How far?

Distances in space are so large that kilometres become clumsy, so astronomers measure them by how long light takes to cross them. Light travels about 300 000 km every second: the Moon is 1.3 light-seconds away and the Sun 8.3 light-minutes. A light-year, about 9.46 million million km, is the distance light travels in a year. Because light takes time to arrive, we see every object as it was when its light left, so looking further away means looking further back in time. Students put twelve objects in order of distance, from the Moon to the most distant galaxies, then work with light-years.

We are learning to

• use light travel time and light-years to describe distances in space,
• put objects in the universe in order of distance,
• explain why seeing far away means seeing into the past.

Success criteria

• I can order twelve objects from the nearest to the most distant, and explain how I compared their distances.
• I can turn a light travel time into a distance in kilometres.

You need

• the distance cards (third sheet), one set per pair, with scissors,
• the worksheet (next sheet), one per student; calculators.

Lesson flow (about 60 minutes)

Running two half-sessions instead? Do Mars, the board and the line-up in Session A, and Parts B and C in Session B.

Watch for these ideas

• “A light-year is a length of time.” It is a distance: how far light travels in a year.
• “The stars are all about the same distance away.” The stars we see range from a few to thousands of light-years away.
• “We see the stars as they are now.” We see them as they were when their light left, years or centuries ago.

Make it easier, make it bigger

• Easier: sort the cards into four groups first, by unit: light-seconds, light-minutes, light-hours and light-years.
• Bigger: if you sent a radio message to Proxima Centauri today, how old would you be when a reply arrived?

Answers and look-fors

• Part A, nearest to most distant: K, D, F, C, L, A, I, G, J, E, B, H.
• Part B: 1. 300 000 × 60 = 18 000 000 km. 2. 8.3 × 60 × 300 000 ≈ 150 000 000 km. 3. 300 000 × 365 × 24 × 60 × 60 ≈ 9.46 × 10¹² km. 4. 4.2 × 9.46 × 10¹² ≈ 4.0 × 10¹³ km. 5. In about 320 years: its light takes that long to reach us.
• Part C: 1. The distances are so large that numbers in kilometres become unwieldy; light travel time is easier to compare. 2. The light left the galaxy long ago, so we see the galaxy as it was then, not as it is now.
• Bigger: the message takes 4.2 years each way, so the reply arrives about 8.4 years later.

How far?

A. Line up

Lay the twelve cards in order, from the nearest to the most distant. Write the card letters.

B. Light-years

Light travels about 300 000 km every second.

C. Questions

From the Moon to the most distant galaxies

Cut out the twelve cards. Each gives an object and how long its light takes to reach Earth. Lay them in order of distance.

Teacher note: the order is in the plan. Distances in the universe are rounded; the order does not depend on the rounding.

How long ago?

The big bang theory describes a universe that began 13.8 billion years ago, extremely hot and dense, and has been expanding and cooling ever since. A number that large means little until it is squeezed into something familiar. On a cosmic calendar the big bang is at midnight on 1 January and today is midnight at the end of 31 December, so each day stands for about 37.8 million years. The Sun and Earth do not form until September, the dinosaurs die out on 30 December, and all of human history fits into the last minutes of the year. Students work out the calendar date of seven events, several of them recorded in Australian rocks.

We are learning to

• describe what the big bang theory says about the start of the universe,
• use scale and proportion to make sense of very long times,
• place events in the history of the universe in order.

Success criteria

• I can turn an age in years into a date on the cosmic calendar, and show the working.
• I can describe the big bang as the start of an expanding, cooling universe, not an explosion in space.

You need

• the worksheet (next sheet), one per student; calculators,
• the exit tickets (third sheet), cut into four.

Lesson flow (about 60 minutes)

Running two half-sessions instead? Do the guesses, the board and Part A in Session A, and Parts B and C and the ticket in Session B.

Watch for these ideas

• “The big bang was an explosion at one place.” It happened everywhere at once; space itself has been stretching ever since.
• “Everything appeared at the start.” Atoms took hundreds of thousands of years to form, and the first stars about 200 million years.
• “The universe is 4.6 billion years old.” That is the age of the Sun and Earth, about a third of the age of the universe.

Make it easier, make it bigger

• Easier: work out the number of days for each event together, and let students find the month from the table of days.
• Bigger: on the same calendar, how long before midnight on 31 December were you born?

Answers and look-fors

• Part A: (13.8 − 4.6) ÷ 13.8 × 365 ≈ 243.3 days into the year: 1 September.
• Part B: the first stars begin to shine, 6 January; the oldest signs of life: stromatolites in the pilbara, western australia, 30 September; the ediacara animals of south australia, 17 December; the dinosaurs, apart from the birds, die out, 30 December; modern humans appear, 31 December at about 11:48 pm; people are living in australia, 31 December at about 11:57 pm.
• Part C: 1. About 37.8 million years. 2. The last two or three minutes of 31 December. 3. A hot, dense universe that has been expanding and cooling ever since, everywhere at once, not an explosion at one point in space.
• Exit ticket: 1. 13.8 billion years. 2. 1 September. 3. About a third.
• Bigger: about 15 years is about 0.03 of a second before midnight.

How long ago?

Squeeze the 13.8 billion years since the big bang into one year. The big bang is the first moment of 1 January; today is the last moment of 31 December.

A. A worked example

The number of days in each month.

B. Place the events

For the last two events, work out how many minutes before midnight on 31 December they fall.

C. Questions

Exit tickets

Fingerprints of light

White light is a mix of wavelengths, and a prism or a diffraction grating spreads it into a spectrum. A hot, dense object such as a lamp filament gives a continuous rainbow. A hot, thin gas gives only bright lines, at wavelengths set by its atoms: a fingerprint of the element. Cooler gas in front of a hot source absorbs the same wavelengths, leaving dark lines. In 1868 astronomers found a yellow line in sunlight that matched no known element; they named the element helium, after the Greek word for the Sun, and it was found on Earth 27 years later. Students view lamps through diffraction glasses if the school has them, then identify the elements in three mystery spectra.

We are learning to

• describe continuous and line spectra,
• identify elements from the lines in a spectrum,
• explain how astronomers learn what stars and galaxies are made of.

Success criteria

• I can match the lines in a mystery spectrum to the elements that made them.
• I can explain why every line of an element must be present before I say it is there.

You need

• diffraction glasses or grating slides, an ordinary lamp and a fluorescent or street-style lamp, if you have them; never the Sun,
• the worksheet (next sheet), one per student, and the exit tickets (third sheet), cut into four.

Lesson flow (about 60 minutes)

Running two half-sessions instead? Do the lamps, the board and the first mystery in Session A, and the rest in Session B.

Watch for these ideas

• “One matching line proves the element is there.” Different elements can have lines close together; the whole pattern must match.
• “A line spectrum shows the colour of the gas.” It shows exactly which wavelengths the atoms give out.
• “Astronomers need samples to know what stars are made of.” The light carries the fingerprints across any distance.

Make it easier, make it bigger

• Easier: cut the element strips out of a spare worksheet and slide each one under the mystery strip.
• Bigger: a streetlight looks yellow, and its spectrum has one strong yellow line. Which element is in the lamp?

Answers and look-fors

• Part A: the ordinary lamp gives a continuous rainbow; the fluorescent lamp gives bright lines over a fainter rainbow.
• Part B: A (a hot star): hydrogen and helium; B (a street lamp): sodium and mercury; C (the sun (some of its dark lines)): hydrogen and sodium.
• Part C: 1. Two elements can have lines very close together, so one line could belong to either; the full pattern only fits one. 2. By spreading the star’s light into a spectrum and matching its lines to elements measured in the lab. 3. Its lines were seen in sunlight, which matched no element known on Earth at the time.
• Exit ticket: 1. Bright lines at certain wavelengths. 2. The pattern of lines (its spectrum). 3. Hydrogen.
• Bigger: sodium.

Fingerprints of light

A. Look at lamps

Through diffraction glasses, look at two lamps (never the Sun). Describe each spectrum.

B. Four elements, three mysteries

Each strip shows where an element’s bright lines fall, in nanometres (nm). Hold a ruler upright to line up the strips.

C. Questions

Exit tickets

Redshift

When a source of light moves away from us, its waves are stretched: every line in its spectrum shifts to a longer wavelength, towards the red end. That is redshift. A source coming towards us is blueshifted. The size of the shift gives the speed: speed = (shift ÷ normal wavelength) × the speed of light. In the 1910s Vesto Slipher found that most galaxies are redshifted, so almost all of them are moving away from us; a few nearby ones, such as Andromeda, are blueshifted, pulled towards us by gravity. Students measure the hydrogen line in five galaxies and work out their speeds. The measurements are example values.

We are learning to

• explain redshift and blueshift,
• calculate the speed of a galaxy from the shift of a spectral line,
• explain what the redshift of most galaxies suggests about the universe.

Success criteria

• I can find the shift of a line and turn it into a speed, showing my working.
• I can say whether a galaxy is moving towards us or away, and how I know.

You need

• the worksheet (next sheet), one per student; calculators,
• the exit tickets (third sheet), cut into four.

Lesson flow (about 60 minutes)

Running two half-sessions instead? Do the siren, the board and Part A in Session A, and Parts B and C and the ticket in Session B.

Watch for these ideas

• “Redshifted galaxies look red.” The lines shift a little; the galaxy’s colour hardly changes to the eye.
• “Every galaxy is moving away.” Almost all are; a few close neighbours, such as Andromeda, are coming towards us.
• “The shift tells us how far away a galaxy is.” It tells us its speed; Lesson 5 links speed to distance.

Make it easier, make it bigger

• Easier: give the shift column filled in, so students only turn the shifts into speeds.
• Bigger: the hydrogen line at 486.1 nm in Galaxy T shifts too. Predict where it is, using the same fraction.

Answers and look-fors

• Part B: Galaxy P, shift 6.6 nm, about 3 000 km/s away; Galaxy Q, shift 13.1 nm, about 6 000 km/s away; Galaxy R, shift -0.7 nm, about 300 km/s towards us; Galaxy S, shift 19.7 nm, about 9 000 km/s away; Galaxy T, shift 32.8 nm, about 15 000 km/s away.
• Part C: 1. Galaxy R: its line is at a shorter wavelength than in the lab, a blueshift. 2. Galaxy T, about 15 000 km/s. 3. Almost all galaxies are moving away from us, which suggests the universe is expanding.
• Exit ticket: 1. The galaxy is moving away. 2. It is coming towards us. 3. (6.6 ÷ 656.3) × 300 000 ≈ 3000 km/s.
• Bigger: 486.1 × (689.1 ÷ 656.3) ≈ 510.4 nm.

Redshift

A. Lab and galaxies

Three of hydrogen’s lines as measured in a lab, and the same lines in the light of five galaxies. These are example measurements.

B. How fast?

In the lab the line is at 656.3 nm. Shift = measured − 656.3. Speed = (shift ÷ 656.3) × 300 000 km/s. Round to the nearest 100 km/s.

C. Questions

Exit tickets

Hubble’s law

Henrietta Leavitt found a way to measure the distance to far-off stars, Vesto Slipher measured the redshifts of galaxies, and in 1927 Georges Lemaître and in 1929 Edwin Hubble put the two together: the further away a galaxy is, the faster it is moving away. Speed against distance makes a straight line through the origin, and its gradient, the Hubble constant, is about 70 km/s for every megaparsec (about 3.26 million light-years). Since 2018 astronomers have called it the Hubble–Lemaître law. Run the expansion backwards at that rate and every galaxy was together about 14 billion years ago, close to the 13.8 billion years from other evidence. Students graph example data, find the gradient and estimate the age.

We are learning to

• graph speed against distance and describe the relationship,
• find the gradient of a line of best fit and say what it means,
• use the Hubble constant to estimate the age of the universe, and name the assumptions.

Success criteria

• I can draw a line of best fit through the origin and find its gradient with units.
• I can explain how the gradient leads to an age for the universe.

You need

• the worksheet (next sheet), one per student, with a ruler and a calculator,
• the exit tickets (third sheet), cut into four.

Lesson flow (about 60 minutes)

Running two half-sessions instead? Do the runners, the board and the graph in Session A, and Parts C and D and the ticket in Session B.

Watch for these ideas

• “The galaxies are flying away from us because we are at the centre.” Every galaxy would see the same pattern; Lesson 6 shows why.
• “The points should sit exactly on the line.” Distances are hard to measure, and galaxies have their own motions too.
• “1 ÷ H₀ is exactly the age.” It assumes the expansion rate never changed; it is an estimate.

Make it easier, make it bigger

• Easier: give the gradient as 70 and go straight to the age calculation.
• Bigger: two methods give the Hubble constant as about 67 and about 73 km/s per megaparsec. Work out the age from each.

Answers and look-fors

• Part A: the points rise in a nearly straight line through the origin.
• Part B: the gradient is about 69.3 km/s per megaparsec (anything from 65 to 75 is a good fit by eye).
• Part C: 1 megaparsec ÷ 70 km/s = 3.09 × 10¹⁹ ÷ 70 ≈ 4.4 × 10¹⁷ s; ÷ 3.16 × 10⁷ s a year ≈ 14 billion years.
• Part D: 1. A galaxy at zero distance, our own, is not moving away from itself. 2. Measurement uncertainty in the distances, and each galaxy’s own motion through space. 3. That the galaxies have moved away at the same speed all along.
• Exit ticket: 1. The further away, the faster it moves away. 2. About 14 000 km/s. 3. About 70 km/s for every megaparsec.
• Bigger: 67 gives about 14.6 and 73 gives about 13.4 billion years.

Hubble’s law

A. Graph it

Six galaxies: their distances and the speeds at which they move away. These are example measurements.

B. The gradient

C. How old is the universe?

D. Questions

Exit tickets

Expanding space

Hubble’s law has a simple cause: space itself is stretching. A balloon with dots drawn on it is a good model. As it is blown up, every dot moves away from every other dot, and a dot twice as far away moves away twice as fast, so the law appears by itself. No dot is at the centre: from any dot, the others all seem to be moving away. Students measure the distances between dots before and after blowing the balloon up further, from two different dots, and then judge the model: the balloon’s surface is two-dimensional, it expands into the room around it, and the drawn dots stretch too, while real galaxies, held together by gravity, do not.

We are learning to

• use a model to explain why more distant galaxies move away faster,
• explain why the expansion of the universe has no centre,
• describe the strengths and the limits of a model.

Success criteria

• I can show from my measurements that the change in distance grows in step with the starting distance.
• I can name two ways the balloon is not like the universe.

You need

• for each pair: a round latex-free balloon, a marker, a piece of string and a ruler; blown up by hand and kept away from faces,
• the worksheet (next sheet), one per student, and the class results sheet (third sheet), on the board or a bench.

Lesson flow (about 60 minutes)

Running two half-sessions instead? Do the bread, the board and the balloons in Session A, and Parts B and C in Session B.

Watch for these ideas

• “The galaxies are moving through space away from a centre.” Space between them stretches; there is no centre and no edge.
• “The universe is expanding into something.” The balloon expands into the room; the universe is not inside anything.
• “Everything is expanding, including us.” Gravity and other forces hold galaxies, stars, planets and people together.

Make it easier, make it bigger

• Easier: measure only from dot A, and fill in the change column together.
• Bigger: draw a dot on the balloon as a whole galaxy, a big blob. What happens to it, and why does that make the model wrong for galaxies?

Answers and look-fors

• Part A: results vary; each distance should roughly double, and the change should grow with the starting distance.
• Part B: A to B changed by 2.2 cm, 1.1 times its starting distance; A to C changed by 3.9 cm, 0.98 times its starting distance; A to D changed by 6.1 cm, 1.02 times its starting distance; A to E changed by 8 cm, 1 times its starting distance: about the same each time.
• Part C: 1. The further apart two dots start, the more they separate in the same time: they move apart faster. 2. No: measured from C, the other dots move away in the same way. 3. Any two: the surface is two-dimensional; the balloon expands into the room around it; it has a centre inside it; the dots stretch, but galaxies do not; real expansion has gone on for 13.8 billion years.
• Bigger: the blob stretches too; real galaxies keep their size because gravity holds them together.

Expanding space

A. Our balloon

Half blow up the balloon and pinch it closed. Mark five small dots, A to E, spread over one side. Measure along the surface with string, then against a ruler. Blow the balloon up further, and measure again.

B. An example class

C. Questions

Class results: change ÷ before

Each pair adds its “change ÷ before” for the four distances from dot A. Are the numbers in each row about the same?

If the numbers across a row are about equal, the change grew in step with the starting distance: Hubble’s law in a balloon.

The leftover glow

Run the expansion backwards and the universe was hotter and denser. For about its first 380 000 years it was so hot that light could not travel far before bumping into something. When it cooled to about 3000 K, atoms formed and the light streamed free. That light has travelled ever since, and the expansion of space has stretched its wavelengths about 1100 times, so it now reaches us as faint microwaves from every direction, at 2.725 K. It was predicted in 1948 and found by accident in 1964. Students follow the story of the prediction and the discovery and work out how far the light has been stretched.

We are learning to

• explain where the cosmic microwave background came from,
• explain why a prediction that is later confirmed is strong evidence,
• calculate how much the expansion of space has stretched the glow.

Success criteria

• I can explain why the glow from a gas at about 3000 K now reaches us as microwaves.
• I can explain why the discovery counted so strongly for the big bang model.

You need

• the worksheet (next sheet), one per student; calculators,
• the exit tickets (third sheet), cut into four.

Lesson flow (about 60 minutes)

Running two half-sessions instead? Do the oven, the board and Part A in Session A, and Parts B and C and the ticket in Session B.

Watch for these ideas

• “The glow comes from the place where the big bang happened.” It comes from every direction, because the early universe was everywhere.
• “Microwaves mean it is hot, like a microwave oven.” At 2.725 K the glow is extremely cold; ovens use the same kind of radiation, much stronger.
• “The glow was discovered and then explained.” It was predicted first, which is what made the discovery such strong evidence.

Make it easier, make it bigger

• Easier: give the two wavelengths in Part B and ask only for the stretch.
• Bigger: the warm and cool patches differ by only about one part in 100 000. Why does it matter that the glow is not perfectly smooth?

Answers and look-fors

• Part A: 1. 1948, about 16 years before it was found. 2. It came from every direction, day and night, so it was not from the Earth, the Sun or the galaxy. 3. They ruled out every ordinary cause, including the antenna itself and the pigeons, before claiming anything.
• Part B: then 0.0029 ÷ 3000 ≈ 0.97 µm (just beyond red, near infrared); now 0.0029 ÷ 2.725 ≈ 1.06 mm (microwaves); stretch 3000 ÷ 2.725 ≈ 1100.
• Part C: 1. It fills the whole sky, behind every star and galaxy. 2. The big bang model predicted it before it was found, and the rival steady state model had no way to make it. 3. Space has stretched about 1100 times since the light was released, stretching its wavelength from near infrared to microwaves.
• Exit ticket: 1. From the hot early universe, when atoms first formed. 2. About 2.725 K (about −270 °C). 3. The expansion of space stretched its wavelength.
• Bigger: the slightly denser patches were where gravity gathered matter into the first galaxies; without them there would be no galaxies.

The leftover glow

A. Predicted, then found

B. Stretched light

A glowing object gives out most strongly at a peak wavelength: peak wavelength (m) = 0.0029 ÷ temperature (K).

C. Questions

Exit tickets

Where the elements came from

For its first few minutes the universe was hot and dense enough for nuclear fusion, but it cooled and thinned so fast that almost nothing heavier than helium was made. The big bang model predicts that, by mass, about 75% of that first matter was hydrogen and about 25% helium, with only a trace of anything heavier, and that is what astronomers measure in the oldest stars and in distant clouds of gas. Every heavier element was made later: carbon, oxygen and nitrogen by fusion inside stars, and the heaviest, such as gold and uranium, in exploding stars and colliding neutron stars. Apart from hydrogen, the atoms in our bodies were made in stars. Students colour the first minutes’ matter and sort twelve elements by where they were made.

We are learning to

• describe what the big bang model predicts about the first elements,
• explain how a match between prediction and measurement supports a model,
• describe where the heavier elements were made.

Success criteria

• I can give the share of hydrogen and helium made in the first minutes, and say how astronomers checked it.
• I can sort elements by where they were made, and explain one card.

You need

• coloured pencils in two colours; the element cards (third sheet), one set per pair, with scissors,
• the worksheet (next sheet), one per student.

Lesson flow (about 60 minutes)

Running two half-sessions instead? Do the hand, the board and Part A in Session A, and Parts B and C in Session B.

Watch for these ideas

• “All the elements were made in the big bang.” Only the lightest were; everything heavier was made later, in stars.
• “Stars burn like fires.” Stars shine by nuclear fusion, joining light nuclei into heavier ones, not by burning.
• “Most of the universe is like Earth.” Earth is rich in heavier elements; the universe as a whole is still mostly hydrogen and helium.

Make it easier, make it bigger

• Easier: give the first two cards of each pile as examples before the sort.
• Bigger: the Sun is about 98% hydrogen and helium. Why does it have a little more of the heavier elements than the oldest stars?

Answers and look-fors

• Part A: 75 squares for hydrogen and 25 for helium. 1. In the oldest stars and in distant gas clouds, which formed before stars had added much else. 2. The universe expanded and cooled so fast that fusion stopped after a few minutes.
• Part B: the first minutes C, G, L; inside stars A, D, F, I, K; exploding stars and colliding neutron stars B, E, H, J.
• Part C: 1. Its prediction, worked out from the physics of the first minutes, matches what is measured, and it could have failed to. 2. Any two of carbon, oxygen, nitrogen, calcium and iron: made in stars that lived and died before the Sun formed, then spread through space. 3. They were made in exploding stars and colliding neutron stars, and scattered into the gas cloud that became the Sun and its planets.
• Bigger: the Sun formed from gas already mixed with heavier elements made by earlier generations of stars.

Where the elements came from

A. The first matter

B. Sort the element cards

C. Questions

Where was each element made?

Cut out the three headings and the twelve cards. Sort each element under the place where most of it was made.

Teacher note: the answer letters are in the plan. The three piles are different sizes.

Weighing the evidence

In the late 1940s the big bang model had a serious rival. In the steady state theory of Fred Hoyle, Hermann Bondi and Thomas Gold, the universe expands but new matter keeps appearing to fill the gaps, so it has no beginning and always looks the same. Hoyle coined the name “big bang” on BBC radio in 1949, partly in fun. Both models explain the redshift of galaxies, so redshift alone could not decide between them. But the two models make different predictions: only the big bang predicts a leftover glow, a young-looking distant universe and the measured mix of light elements. Students match six predictions with what was later observed, then judge which model each observation supports.

We are learning to

• match a model’s predictions with observations,
• use evidence to decide between two models,
• explain why scientists accept a model, and what could change their minds.

Success criteria

• I can match each prediction with the observation that tested it.
• I can explain which observation the steady state theory could not account for, and why that mattered.

You need

• the prediction cards (third sheet), one set per pair, with scissors,
• the worksheet (next sheet), one per student.

Lesson flow (about 60 minutes)

Running two half-sessions instead? Do the stories, the board and the matching in Session A, and Parts B and C in Session B.

Watch for these ideas

• “The big bang is just a theory, so it is a guess.” In science a theory is a well-tested explanation that has passed many tests.
• “One observation proves the model.” It is the agreement of several separate lines of evidence that makes the case.
• “Scientists will never change their minds.” The model has been refined many times and would change if new evidence demanded it.

Make it easier, make it bigger

• Easier: match the first pair together, reading both cards aloud.
• Bigger: two methods give slightly different values for the Hubble constant. Is that a problem for the big bang model, or a chance to refine it?

Answers and look-fors

• Part A: G with A, D with J, E with L, B with H, K with F, I with C.
• Part B: the big bang model expects all six observations; the steady state theory expects only the first, the redshift that grows with distance.
• Part C: 1. The microwave glow: steady state had no hot past to leave one, and the glow was predicted by the big bang before it was found. 2. It made clear, testable predictions; several separate kinds of observation match them; and it could have failed. 3. For example, a star or galaxy clearly older than 13.8 billion years, or a glow that did not fit the predicted pattern.
• Bigger: a refinement to work on: the model is kept, and the disagreement points to measurements or details still to be understood.

Weighing the evidence

A. Match

Pair each prediction card with the observation that tested it. Write the pairs of letters.

B. Which model?

For each observation, tick each model that expects it.

The steady state theory: the universe expands, but new matter keeps appearing, so it has no beginning and always looks the same.

C. Questions

Predictions and observations

Cut out the twelve cards. Six are predictions of the big bang model; six are what astronomers later observed. Match each pair.

Teacher note: the pairs are in the plan. Every card has exactly one partner.

Show what we know

The term comes together. In the task, students survey five galaxies: from the measured wavelength of the hydrogen line they find each galaxy’s shift, its speed, and then its distance from Hubble’s law. They describe the three lines of evidence for the big bang and answer a news claim that the big bang was an explosion at the centre of the universe. Then they sit the eight-question final check, and the class plays the unit quiz as a game on the board.

We are learning to

• turn a redshift into a speed and a distance,
• explain the evidence for the big bang model,
• use evidence to answer a claim about the big bang.

Success criteria

• I can complete the survey table, showing my working for one galaxy.
• I can answer the final check on my own.

You need

• the task (next sheet) and the final check (third sheet), one each per student; calculators,
• the interactive unit open on the board for the quiz; mini whiteboards if you have them.

Lesson flow (about 60 minutes)

Running two half-sessions instead? Do the recall and the task in Session A, and the final check and the quiz in Session B.

Watch for these ideas

• Students who divide by 70 before working out the speed: speed first, from the shift; then distance from the speed.
• Students who agree with the news claim because the galaxies all move away from us: every galaxy would see the same.
• Students who list redshift twice, as expansion and as Hubble’s law: the three lines are redshift, the glow and the light elements.

Make it easier, make it bigger

• Easier: give the shift column filled in.
• Bigger: Galaxy 5 is 200 megaparsecs away. How long has its light been travelling, in years? (1 megaparsec is about 3.26 million light-years.)

Answers and look-fors

• Task table: Galaxy 1, shift 3.1 nm, 1 400 km/s, 20 Mpc; Galaxy 2, shift 6.1 nm, 2 800 km/s, 40 Mpc; Galaxy 3, shift 12.3 nm, 5 600 km/s, 80 Mpc; Galaxy 4, shift 18.4 nm, 8 400 km/s, 120 Mpc; Galaxy 5, shift 30.6 nm, 14 000 km/s, 200 Mpc.
• Task questions: 2. The further away, the faster: speed is about 70 km/s for each megaparsec. 3. The redshift of galaxies, growing with distance; the cosmic microwave background, the glow left from the hot early universe; and the mix of about 75% hydrogen and 25% helium made in the first minutes. 4. Space itself is stretching everywhere, so every galaxy sees every other galaxy moving away; there is no centre, and the big bang happened everywhere, not at one point.
• Final check: 1. 13.8 billion years. 2. The distance light travels in a year, about 9.46 × 10¹² km. 3. the galaxy is moving away from us. 4. 100 × 70 = 7000 km/s. 5. Redshift growing with distance, the cosmic microwave background, and the amounts of hydrogen and helium. 6. hydrogen. 7. The expansion of space has stretched its wavelength about 1100 times. 8. Space itself stretches everywhere at once, so from any galaxy the others all move away; none is at the centre.
• Bigger: 200 × 3.26 million ≈ 652 million years.
• Mark the task against the rubric in the assessment kit; the check covers scale, expansion, evidence and the model.

A survey of five galaxies

An astronomer measures the hydrogen line, 656.3 nm in the lab, in the light of five galaxies. These are example measurements.

Show what we know