Astronomy Vocabulary Quiz
12 multiple-choice questions on stars, planets, galaxies, space phenomena and scientific terms used in astronomy. B2 level. Great for science enthusiasts and IELTS Academic preparation.
Keep building your astronomy vocabulary.
Astronomy Vocabulary — FAQ
A planet is a celestial body that orbits a star, has sufficient mass to be roughly spherical, and has cleared the neighbourhood around its orbit of other debris. A dwarf planet meets the first two criteria but has not cleared its orbital neighbourhood. Pluto was reclassified from planet to dwarf planet by the International Astronomical Union (IAU) in 2006 because it shares its orbital zone with other Kuiper Belt objects.
A light-year is a unit of distance, not time — despite containing the word 'year'. It is the distance that light travels in one year in a vacuum, approximately 9.46 trillion kilometres (5.88 trillion miles). Astronomers use light-years because the distances between stars and galaxies are so enormous that kilometres would be impractical. The nearest star to the Sun, Proxima Centauri, is about 4.24 light-years away.
A solar system is a star and all the celestial objects gravitationally bound to it, including planets, dwarf planets, moons, asteroids, comets and interplanetary dust. Our solar system contains the Sun, eight planets (Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus and Neptune), more than 200 moons, and billions of smaller bodies in the asteroid belt and Kuiper Belt.
Both asteroids and comets are small solar system bodies, but they differ in composition and origin. Asteroids are rocky or metallic objects, most of which orbit the Sun in the asteroid belt between Mars and Jupiter. Comets are icy bodies from the outer solar system (Kuiper Belt or Oort Cloud) that develop a bright tail of gas and dust when they pass close to the Sun and the ice vaporises. The tail always points away from the Sun.
A black hole is a region of space where gravity is so strong that nothing — not even light — can escape it once it has crossed the event horizon (the boundary around a black hole). Black holes form when massive stars collapse at the end of their lives. They cannot be observed directly because they emit no light, but their presence is detected through their gravitational effects on nearby stars and gas, and through the emission of X-rays from matter falling into them.
An orbit is the curved path that one object takes around another object due to gravity — for example, the Earth orbits the Sun once every 365.25 days. Rotation refers to an object spinning on its own axis — for example, the Earth rotates once every 24 hours, giving us day and night. The Moon both orbits the Earth and rotates on its axis, but its rotation period equals its orbital period, which is why we always see the same side of the Moon from Earth.
A star is a massive ball of plasma that generates its own light and heat through nuclear fusion in its core. The Sun is the closest star to Earth. A planet is a much smaller body that orbits a star and does not produce its own light — it only reflects the light of its star. Stars appear as fixed points of light in the night sky (though they twinkle due to the atmosphere), while planets can be seen as steady discs through a telescope.
Gravity is the fundamental force of attraction between objects with mass. In astronomy, gravity governs almost everything: it holds planets in orbit around stars, keeps moons orbiting planets, holds galaxies together, causes stars to form from clouds of gas and dust (nebulae), and ultimately determines the life cycle and fate of stars. The strength of gravity between two objects depends on their masses and the distance between them — described by Newton's law of universal gravitation and refined by Einstein's general theory of relativity.
The Milky Way is the galaxy that contains our solar system. It is a barred spiral galaxy estimated to contain between 100 and 400 billion stars. On a clear, dark night it appears as a faint, milky band of light stretching across the sky — this is actually the combined light of billions of distant stars in the disc of our galaxy seen edge-on. Our solar system is located in one of the Milky Way's outer spiral arms, about 26,000 light-years from the galactic centre.
Key astronomy vocabulary: celestial body (any natural object in space), orbit (path around another body), galaxy (system of billions of stars), nebula (cloud of gas and dust where stars form), supernova (explosive death of a massive star), eclipse (one body passing into the shadow of another), atmosphere (layer of gases surrounding a planet), telescope (instrument for observing distant objects), constellation (pattern of stars as seen from Earth), and lunar/solar (relating to the Moon/Sun).