--- title: "Quick check: scale, the cosmic glow and the evidence" subtitle: "Year 10 Earth and space · The big bang · Lesson 6" --- # Quick check: scale, the cosmic glow and the evidence **Name:** {{field-24}} **Date:** {{field-15}} **Class:** {{field-15}} > **Key question:** The light you see from some stars left them before humans existed. How far is that, and what else tells us the universe had a beginning? :::teacher-note **In one sentence:** A self-test on the scale of the universe, the CMB and matter proportions, and how the lines of evidence fit together (AC9S10U03, nodes 1, 4 and 5, taught in class; node 5 a hinge). **Students should be able to say:** I can order the parts of the universe by scale and use light-years and AU. I can say what the CMB and the hydrogen-helium mix show. I can say why several independent lines of evidence strengthen a theory. **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. ::: ## Scale :::keep-together ### Smallest to largest **Which list is in order from smallest to largest?** ☐ Galaxy, star, planet, universe, solar system ☐ Star, planet, galaxy, solar system, universe ☐ Universe, galaxy, solar system, star, planet ☐ Planet, star, solar system, galaxy, universe ::: :::teacher-note **Answer:** Planet, star, solar system, galaxy, universe A planet is part of a solar system around a star; billions of stars make a galaxy; the universe holds billions of galaxies. (A star is larger than a planet.) ::: :::keep-together ### Units **A light-year is a unit of what?** ☐ Speed ☐ Time: one year ☐ Brightness ☐ Distance: how far light travels in a year ::: :::teacher-note **Answer:** Distance: how far light travels in a year Light travels about 9.5 trillion kilometres in a year. The distance, not the time, is the unit. ::: :::keep-together ### Which unit? **Which unit suits the distance from Earth to the Sun?** ☐ Kilogram ☐ Astronomical unit (AU) ☐ Metre ☐ Light-year ::: :::teacher-note **Answer:** Astronomical unit (AU) One AU is the average distance from Earth to the Sun, about 150 million km. Light-years are for distances between stars. ::: :::keep-together ### Scientific notation **The Sun is about 1.5 × 10^8 km from Earth. Written out in full, that is:** ☐ 150 000 000 km ☐ 15 000 000 km ☐ 1 500 000 000 km ☐ 1.5 million km ::: :::teacher-note **Answer:** 150 000 000 km 10^8 is 100 million, so 1.5 × 10^8 is 150 million. ::: ## The cosmic glow and matter :::keep-together ### The glow **The cosmic microwave background is a faint radiation coming from every direction. What does it show?** ☐ Stars are cooling ☐ Earth is surrounded by a hot shell ☐ Space is full of hot gas ☐ The early universe was hot and dense, and has been cooling as it expanded ::: :::teacher-note **Answer:** The early universe was hot and dense, and has been cooling as it expanded This radiation was released when the universe was young and hot. It has cooled and stretched into microwaves. ::: :::keep-together ### What matter is made of **About how much of the mass of ordinary matter in the universe is hydrogen and helium?** ☐ Mostly oxygen and carbon ☐ Mostly heavier elements, made in stars ☐ Almost all of it: by mass, about three-quarters hydrogen and one-quarter helium ☐ Equal parts of every element ::: :::teacher-note **Answer:** Almost all of it: by mass, about three-quarters hydrogen and one-quarter helium The big bang model predicts roughly this mix from the first few minutes, and observations match it. ::: :::keep-together ### Independent evidence **Is it evidence for the big bang that does not depend on redshift?** Groups: Independent evidence, Not independent - The cosmic microwave background: {{field-15}} - The proportions of hydrogen and helium: {{field-15}} - Distant galaxies moving away from us (redshift): {{field-15}} ::: :::teacher-note **Answer:** The cosmic microwave background → Independent evidence; The proportions of hydrogen and helium → Independent evidence; Distant galaxies moving away from us (redshift) → Not independent ::: ## The evidence together :::keep-together ### Match the evidence **Which line of evidence is it?** Groups: Redshift, CMB, Matter proportions - Distant galaxies are moving away from us: {{field-15}} - A faint glow reaches us from every direction: {{field-15}} - About three-quarters of the mass is hydrogen, almost all the rest helium: {{field-15}} - The universe is expanding: {{field-15}} - The early universe was very hot and has cooled: {{field-15}} - Hydrogen and helium nuclei formed in the first few minutes: {{field-15}} ::: :::teacher-note **Answer:** Distant galaxies are moving away from us → Redshift; A faint glow reaches us from every direction → CMB; About three-quarters of the mass is hydrogen, almost all the rest helium → Matter proportions; The universe is expanding → Redshift; The early universe was very hot and has cooled → CMB; Hydrogen and helium nuclei formed in the first few minutes → Matter proportions ::: :::keep-together ### Why it is strong **Why does it strengthen the big bang theory that redshift, the CMB and matter proportions all fit?** ☐ They are all one measurement in three forms ☐ They disprove each other ☐ They are independent lines of evidence that agree on the same model ☐ They prove the theory can never change ::: :::teacher-note **Answer:** They are independent lines of evidence that agree on the same model When different kinds of evidence from different methods point the same way, the model is hard to explain away. ::: :::keep-together ### Still open **Which is still an open question in cosmology?** ☐ What dark matter and dark energy are ☐ Whether other galaxies exist ☐ Whether there is a CMB ☐ Whether the universe is expanding ::: :::teacher-note **Answer:** What dark matter and dark energy are Observations suggest most of the universe is dark matter and dark energy, but scientists do not yet know what they are. ::: ## Exit ticket :::keep-together **Name two lines of evidence for the big bang and what each shows.** {{lines-3}} ::: :::teacher-note **Answer:** Redshift: the universe is expanding. CMB: it was hot and dense early. (Or hydrogen and helium proportions.) :::