Stars, Galaxies and the Universe

The stars you can find in the night sky, plus black holes, galaxies and how the universe began.

Beyond the Solar System, the scale gets hard to hold in your head. This deck works through it one card at a time: what a light-year measures, how stars live and die, which ones are bright in the night sky, what dark matter and dark energy are, and how old the universe is. Explanations come with each answer, so you finish with more than a list of names.

All 45 cards

  1. What is the nearest star to the Sun?

    Proxima Centauri(also Proxima, Alpha Centauri)

    About 4.24 light-years away. It is part of the Alpha Centauri system.

  2. What does a light-year measure?

    Distance: how far light travels in a year, about 9.46 trillion km (5.88 trillion miles).

  3. Light travels at about 300,000 km per second (186,000 miles per second).

    Exactly 299,792,458 metres per second, by definition.

  4. What is the brightest star in the night sky?

    Sirius

    The "Dog Star", in Canis Major, 8.6 light-years away.

  5. What is the North Star’s name?

    Polaris

    It sits almost directly above Earth’s North Pole, so it barely moves through the night. It is not especially bright: about 48th.

  6. The Big Dipper is part of which constellation?

    Ursa Major

    The Great Bear. Its two "pointer" stars lead to Polaris.

  7. Which winter constellation has a belt of three bright stars in a row?

    Orion

    The Hunter, visible from almost everywhere on Earth.

  8. What is the red supergiant at Orion’s shoulder called?

    Betelgeuse

    It will explode as a supernova some time in the next 100,000 years or so.

  9. Which star cluster in Taurus is known as the Seven Sisters?

    The Pleiades(also Pleiades)

  10. How many constellations does the International Astronomical Union recognize?

    88

    They divide the whole sky into regions, like countries on a map.

  11. True or false: Stars twinkle because Earth’s moving air bends their light.

    True

    Planets twinkle less because they appear as tiny discs, not points.

  12. Which colour of star is hottest?

    Blue

    Blue stars can pass 30,000 °C at the surface; red ones are around 3,000 °C.

  13. What powers the Sun?

    Nuclear fusion in its core, turning hydrogen into helium.

    It converts about 4 million tonnes of mass into energy every second.

  14. The Sun is about 4.6 billion years old, roughly halfway through its life.

  15. What will the Sun eventually become?

    A white dwarf

    After swelling into a red giant. It is too small to explode or collapse into a black hole.

  16. What is a supernova?

    The explosion of a star: a massive star collapsing at the end of its life, or a white dwarf that takes on too much matter.

    Many of the heavier elements in your body were made in them.

  17. What is a neutron star?

    The collapsed core left by some supernovae: more mass than the Sun in a ball about 20 km across.

  18. What do we call a spinning neutron star whose beams sweep past Earth like a lighthouse?

    Pulsar

  19. What is a black hole?

    A region where gravity is so strong that nothing, not even light, can escape once inside.

  20. What is the boundary around a black hole, past which nothing escapes, called?

    The event horizon(also Event horizon)

  21. What is the supermassive black hole at the centre of the Milky Way called?

    Sagittarius A*(also Sagittarius A, Sgr A*)

    About 4 million times the mass of the Sun. It was first imaged in 2022.

  22. What is a nebula?

    A cloud of gas and dust in space. Some are where new stars form; others are what dying stars throw off.

  23. What is our galaxy called?

    The Milky Way(also Milky Way)

  24. What kind of galaxy is the Milky Way?

    A barred spiral

  25. The Milky Way is about 100,000 light-years across and holds a few hundred billion stars.

  26. The Sun takes about 230 million years to orbit the centre of the Milky Way.

  27. What is the nearest large galaxy to the Milky Way?

    The Andromeda Galaxy(also Andromeda, M31)

    About 2.5 million light-years away. It is the farthest thing most people can see with the naked eye. It is heading our way.

  28. The universe is about 13.8 billion years old.

  29. What was the Big Bang?

    The rapid expansion from an extremely hot, dense state that began the universe as we know it, about 13.8 billion years ago.

    It was not an explosion into empty space: space itself has been expanding ever since.

  30. What is the cosmic microwave background?

    The afterglow of the Big Bang: light from about 380,000 years after it, now stretched into microwaves and coming from every direction.

  31. Which astronomer’s 1929 measurements showed that galaxies are moving away from us?

    Edwin Hubble(also Hubble)

    Georges Lemaître had predicted the expanding universe two years earlier.

  32. What is redshift?

    Light from something moving away from us is stretched to longer, redder wavelengths.

    The farther away a galaxy is, the stronger its redshift: the key evidence that the universe is expanding.

  33. Ordinary matter makes up only about 5% of the universe. The rest is dark matter (about 27%) and dark energy (about 68%).

  34. What is dark matter?

    Matter that gives off no light but whose gravity we can measure, holding galaxies together.

    There is about five times as much of it as ordinary matter. What it is made of is still unknown.

  35. What is dark energy?

    The unknown cause of the universe’s expansion speeding up.

    Discovered in 1998 from distant supernovae, and still one of the biggest open questions in physics.

  36. Which infrared space telescope, launched in 2021, orbits 1.5 million km from Earth?

    James Webb Space Telescope(also James Webb, Webb, JWST)

  37. In what year was the Hubble Space Telescope launched?

    1990

    Its mirror turned out to be slightly misshapen; astronauts fitted corrective optics in 1993.

  38. What is an exoplanet?

    A planet that orbits a star other than the Sun.

    The first around a Sun-like star was found in 1995; more than 6,000 are now confirmed.

  39. True or false: A shooting star is a star falling through the sky.

    False

    It is a meteor: a grain of space dust or rock burning up in the atmosphere.

  40. Meteoroid, meteor, meteorite: what is the difference?

    Meteoroid: the rock out in space. Meteor: its streak of light in the atmosphere. Meteorite: what reaches the ground.

  41. Which way does a comet’s tail point?

    Away from the Sun, whichever way the comet is moving.

    Sunlight and the solar wind push the gas and dust that the Sun’s heat drives off it.

  42. Which famous comet comes back about every 76 years, next in 2061?

    Halley’s Comet(also Halley, Halleys comet, Comet Halley)

  43. True or false: Astronauts float on the space station because there is no gravity there.

    False

    Gravity at the station’s height is about 90% of what it is on the ground. They float because they are falling around Earth together with the station.

  44. What is the Sun’s outer atmosphere, seen during a total eclipse, called?

    The corona(also Corona)

    Oddly, it is millions of degrees, far hotter than the surface below it.

  45. What causes the northern and southern lights?

    Charged particles from the Sun, steered by Earth’s magnetic field toward the poles, make gases in the upper atmosphere glow.

    Oxygen gives the green and red; nitrogen gives blue and purple.