Collection · COL-11

The Sun and the Stars

How stars are born, what the Sun throws into space, what's left when a massive star collapses, how sunlight can push a spacecraft, the plasma clouds the Sun hurls at Earth and the black holes that light up quasars.

11 case files · 22 quiz questions · Space, Science, Tech

11 case files in this collection

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Free PDF: every quick fact with its ID, the write-ups, sources and a quiz with an answer key.

What Is in The Sun and the Stars?

11 case files from the Space department, in order: a cold cloud collapsing into a star, the magnetic plasma loops and eruptions of the Sun, the spinning neutron stars left behind when massive stars explode, and sails that turn sunlight into thrust. Stars are born in molecular clouds as cold as 10 to 20 K, which must be squeezed by a factor of nearly 10^20 in density to make a star. DD-037 When a prominence erupts it becomes the bright core of a coronal mass ejection, which can reach Earth in as little as 15 to 18 hours. DD-038 Photons have no mass but carry momentum, so a mirror-like sail gets pushed twice: once when light hits it and again when it bounces off. DD-039

The Case Files, in Order

  1. 01
    DID YOU
    KNOW?    Stellar BirthDD-037

    DD-037Space+ Science

    Stellar Birth

    Every star starts as a cold cloud that collapses.

    Open case file →
  2. 02
    DID YOU
    KNOW?    Solar ProminenceDD-038

    DD-038Space+ Science

    Solar Prominence

    Magnetic fields hold rivers of plasma above the sun.

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  3. 03
    DID YOU
    KNOW?    Neutron SpinDD-058

    DD-058Space+ Science

    Neutron Spin

    Dead stars that spin hundreds of times a second.

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  4. 04
    DID YOU
    KNOW?    Solar SailingDD-039

    DD-039Space+ Tech

    Solar Sailing

    This spacecraft is pushed by sunlight alone.

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  5. 05
    DID YOU
    KNOW?    Coronal Mass EjectionDD-091

    DD-091Space+ Science

    Coronal Mass Ejection

    The Sun sometimes throws off billions of tons of itself.

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  6. 06
    DID YOU
    KNOW?    Quasi-StellarDD-106

    DD-106Space+ Science

    Quasi-Stellar

    Some of the brightest objects in the universe are feeding black holes.

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  7. 07
    DID YOU
    KNOW?    NebulaDD-087

    DD-087Space

    Nebula

    Stars are born when parts of a nebula collapse.

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  8. 08
    DID YOU
    KNOW?    Event HorizonDD-089

    DD-089Space+ Science

    Event Horizon

    Nothing, not even light, escapes from inside an event horizon.

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  9. 09
    DID YOU
    KNOW?    striking!DD-393

    DD-393Space

    striking!

    Researchers estimate about 17 meteorites reach the ground each day.

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  10. 10
    DID YOU
    KNOW?    433 ErosDD-380

    DD-380Space

    433 Eros

    Asteroid 433 Eros is about 34 kilometers long.

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  11. 11
    DID YOU
    KNOW?    Lunar TopographyDD-385

    DD-385Space

    Lunar Topography

    With no air or water, the Moon's craters barely erode.

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Collection Quiz

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22 questions from all 11 case files in The Sun and the Stars. Test Your Knowledge: answers are revealed instantly.

  1. How cold are the molecular clouds where stars are born?

    1. About 10–20 K
    2. About 300 K
    3. About 1,000 K
    4. About 1 million K
    Show the answer

    Answer: A. About 10–20 K Now You Know: They're the coldest, densest parts of interstellar space. Source: DD-037 · Stellar Birth · Write-up · Exhibit A (Stellar nurseries) · Stellar Evolution: Cycles of Formation and Destruction (NASA Chandra X-ray Center); 21.1 Star Formation, Astronomy 2e (OpenStax)

  2. What is the main ingredient of a molecular cloud?

    1. Helium
    2. Molecular hydrogen
    3. Water vapor
    4. Iron
    Show the answer

    Answer: B. Molecular hydrogen Now You Know: That's why they're called molecular clouds, with dust mixed in. Source: DD-037 · Stellar Birth · Write-up · Exhibit A (Stellar nurseries) · Stellar Evolution: Cycles of Formation and Destruction (NASA Chandra X-ray Center); 21.1 Star Formation, Astronomy 2e (OpenStax)

  3. What is a solar prominence called when it's seen against the face of the sun?

    1. A sunspot
    2. A filament
    3. A flare
    4. A corona
    Show the answer

    Answer: B. A filament Now You Know: It's the same structure. Against the bright disk it looks like a dark thread. Source: DD-038 · Solar Prominence · Write-up · Exhibit A (What a prominence is) · What is a solar prominence? (NASA, 2015)

  4. What holds a prominence up above the sun's surface?

    1. Solar wind
    2. Twisted magnetic fields
    3. Gravity waves
    4. Nuclear fusion
    Show the answer

    Answer: B. Twisted magnetic fields Now You Know: Prominence plasma flows along twisted magnetic structures anchored in the photosphere. Source: DD-038 · Solar Prominence · Write-up · Exhibit B (Held up by magnetism) · What is a solar prominence? (NASA, 2015); Prominences: The Key to Understanding Solar Activity (NASA Technical Reports Server)

  5. Who first proposed neutron stars, in 1933?

    1. Einstein and Bohr
    2. Baade and Zwicky
    3. Bell and Hewish
    4. Hubble and Sagan
    Show the answer

    Answer: B. Baade and Zwicky Now You Know: They tied them to supernovae. Source: DD-058 · Neutron Spin · Write-up · Exhibit A (Born in a collapse) · Kaspi & Kramer, Radio Pulsars: The Neutron Star Population & Fundamental Physics (arXiv, 2016); Pulsars (NASA Science, Hubble)

  6. What makes a collapsing core spin faster?

    1. Magnetism alone
    2. Conservation of angular momentum
    3. Dark matter
    4. Solar wind
    Show the answer

    Answer: B. Conservation of angular momentum Now You Know: It's like a skater pulling in her arms. Source: DD-058 · Neutron Spin · Write-up · Exhibit B (Why they spin fast) · Pulsars (NASA Science, Hubble); Kaspi & Kramer, Radio Pulsars: The Neutron Star Population & Fundamental Physics (arXiv, 2016)

  7. What pushes a solar sail?

    1. The solar wind
    2. The momentum of sunlight
    3. Magnetic fields
    4. A small rocket
    Show the answer

    Answer: B. The momentum of sunlight Now You Know: Photons carry momentum. The solar wind's push is less than one percent as strong. Source: DD-039 · Solar Sailing · Write-up · Exhibit A (Massless but pushy) · What is solar sailing? (The Planetary Society); How do photons propel solar sails? (Astronomy, 2020)

  8. Why does a reflective sail get a bigger push than a black one?

    1. It's lighter
    2. Photons push again when they bounce off
    3. It's hotter
    4. It's magnetic
    Show the answer

    Answer: B. Photons push again when they bounce off Now You Know: Light pushes once on arrival and again on reflection. Source: DD-039 · Solar Sailing · Write-up · Exhibit A (Massless but pushy) · What is solar sailing? (The Planetary Society); How do photons propel solar sails? (Astronomy, 2020)

  9. Where do CMEs come from?

    1. The Sun's corona
    2. Earth's core
    3. Jupiter
    4. The Moon
    Show the answer

    Answer: A. The Sun's corona Now You Know: The Sun's outer atmosphere. Source: DD-091 · Coronal Mass Ejection · Write-up · Exhibit A (From the corona) · NOAA SWPC: Coronal Mass Ejections; Wikipedia: Coronal mass ejection

  10. How much material can a CME eject?

    1. Billions of tons
    2. A few kilograms
    3. One ton
    4. Nothing measurable
    Show the answer

    Answer: A. Billions of tons Now You Know: Per NOAA's SWPC. Source: DD-091 · Coronal Mass Ejection · Write-up · Exhibit B (Billions of tons) · NOAA SWPC: Coronal Mass Ejections

  11. What powers a quasar?

    1. A supermassive black hole
    2. A neutron star
    3. A comet
    4. A planet
    Show the answer

    Answer: A. A supermassive black hole Now You Know: Via its accretion disk. Source: DD-106 · Quasi-Stellar · Write-up · Exhibit A (Active nuclei) · Wikipedia: Quasar

  12. Where are quasars found?

    1. At galaxy centers
    2. In our solar system
    3. On the Moon
    4. In nebulae only
    Show the answer

    Answer: A. At galaxy centers Now You Know: Active galactic nuclei. Source: DD-106 · Quasi-Stellar · Write-up · Exhibit B (Black holes) · Wikipedia: Quasar

  13. What is a nebula?

    1. A cloud of gas and dust
    2. A planet
    3. A comet
    4. A black hole
    Show the answer

    Answer: A. A cloud of gas and dust Now You Know: Interstellar. Source: DD-087 · Nebula · Write-up · Exhibit A (Clouds) · Wikipedia: Nebula

  14. Which type glows?

    1. Emission
    2. Dark
    3. Reflection
    4. None
    Show the answer

    Answer: A. Emission Now You Know: Ionized gas. Source: DD-087 · Nebula · Write-up · Exhibit B (Types) · Wikipedia: Nebula

  15. What can escape an event horizon?

    1. Nothing
    2. Light
    3. Radio waves
    4. Neutrinos
    Show the answer

    Answer: A. Nothing Now You Know: Not even light. Source: DD-089 · Event Horizon · Write-up · Exhibit A (Boundary) · Wikipedia: Event horizon

  16. What is at the center?

    1. A predicted singularity
    2. A star
    3. A planet
    4. Nothing at all
    Show the answer

    Answer: A. A predicted singularity Now You Know: Per relativity. Source: DD-089 · Event Horizon · Write-up · Exhibit B (Light) · Wikipedia: Event horizon; Wikipedia: Black hole

  17. About how many reach the ground daily?

    1. 17
    2. 1
    3. 1,000
    4. None
    Show the answer

    Answer: A. 17 Now You Know: 2020 estimate. Source: DD-393 · striking! · Write-up · Exhibit A (Daily) · Wikipedia: Meteorite

  18. Which crater is tied to the dinosaurs?

    1. Chicxulub
    2. Meteor Crater
    3. Vredefort
    4. Tycho
    Show the answer

    Answer: A. Chicxulub Now You Know: Mexico. Source: DD-393 · striking! · Write-up · Exhibit B (Yearly) · Wikipedia: Meteorite

  19. How long is Eros?

    1. About 34 km
    2. About 3 km
    3. About 340 km
    4. About 1 km
    Show the answer

    Answer: A. About 34 km Now You Know: Elongated. Source: DD-380 · 433 Eros · Write-up · Exhibit A (Size) · Wikipedia: 433 Eros

  20. When discovered?

    1. 1898
    2. 1998
    3. 1801
    4. 1950
    Show the answer

    Answer: A. 1898 Now You Know: 19th century. Source: DD-380 · 433 Eros · Write-up · Exhibit B (Discovered) · Wikipedia: 433 Eros

  21. What made the craters?

    1. Impacts
    2. Volcanoes only
    3. Rivers
    4. Wind
    Show the answer

    Answer: A. Impacts Now You Know: Collisions. Source: DD-385 · Lunar Topography · Write-up · Exhibit A (Impacts) · Wikipedia: Lunar craters

  22. Largest basin?

    1. South Pole-Aitken
    2. Tycho
    3. Copernicus
    4. Mare Tranquillitatis
    Show the answer

    Answer: A. South Pole-Aitken Now You Know: Far side. Source: DD-385 · Lunar Topography · Write-up · Exhibit B (Bombardment) · Wikipedia: Lunar craters