What you'll learn from these flashcards
Explore flashcards about planets and moons, comets, stars, galaxies and other objects in the Universe. Images on the cards help you recognize celestial objects and remember them.
Learn how the Solar System is arranged, what makes a meteor different from a meteorite, how asteroids differ from comets and how stars change over time. Return to the cards whenever you want to reinforce or refresh what you have learned.
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The Solar System and the Distant Universe
The Solar System has eight planets. The four closest to the Sun—Mercury, Venus, Earth and Mars—are rocky worlds with solid surfaces. The four farther out are different: Jupiter and Saturn are gas giants, while Uranus and Neptune are ice giants.
- Sun — 1392000 km
- Mercury — 4879 km
- Venus — 12104 km
- Earth — 12756 km
- Mars — 6792 km
- Jupiter — 142984 km
- Saturn — 120536 km
- Uranus — 51118 km
- Neptune — 49528 km
Pluto also orbits the Sun, but since 2006 it has been classified as a dwarf planet: unlike the eight planets, it has not cleared other objects from the neighbourhood of its orbit. One reason the classification was reconsidered was the discovery of Eris, a celestial body almost as large as Pluto. Planets differ not just in size, but also in their distances from the Sun.
- Mercury (0.387 AU)
- Venus (0.723 AU)
- Earth (1 AU)
- Mars (1.52 AU)
- Jupiter (5.20 AU)
- Saturn (9.57 AU)
- Uranus (19.17 AU)
- Neptune (30.18 AU)
But the Solar System contains much more than planets. Asteroids are made mainly of rock and metal; comets contain ice, dust and rocky material. The difference becomes particularly clear when a comet approaches the Sun: its ice begins turning into gas, forming a cloud of gas and dust, and sometimes a tail. Other terms are easy to confuse, too. A meteoroid is a small solid object in space, a meteor is the streak of light produced when it enters an atmosphere, and a meteorite is a surviving fragment that reaches a planet’s surface.
Even the Solar System is only a small part of the Milky Way galaxy. The Sun is one of its billions of stars. Stars have different fates, determined mainly by their mass: the Sun will end its evolution as a white dwarf, while much more massive stars may explode as supernovae, leaving behind a neutron star or a black hole. Some neutron stars are pulsars: as they rotate, we observe their radiation as regular pulses.
What the flashcards look like
The front of a flashcard shows the name of a celestial object or an astronomy term. Try to remember what you know about it, then turn the card over. Where appropriate, the back starts with a short profile of the object’s main properties, followed by an explanation, important and interesting facts, and often an image.
You don’t need to learn anything beforehand. The cards already contain the information you need to get started with astronomy: read the answer first, then try recalling it when you see the card again.
You don’t have to remember everything on the first try. Revisit the cards, practise what you have forgotten and gradually strengthen your knowledge at your own pace.
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Try the ready-made astronomy flashcards: learn names and concepts, test yourself and return to anything you still find difficult.
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