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5.3Chapter 5: The Earth in Space

The night sky — Alhussan Physics - Stage 7 Revision Notes & Topical Questions

5 min read 8 parts Lesson 3 of 11 1 quiz

📚 Alhussan Physics - Stage 7 Hub / Topical Revision
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5.3 The night sky — Stars, Planets, Satellites and Comets — Alhussan International Academy — Physics (Stages 7–9) notes: Name the types of object seen in the night sky and explain how we see them.Stars = huge balls of gas that give out light.Most of the millions of dots of light …

  • Fixed arrangement
  • Properties
  • Seen without a telescope
  • Other planets
  • Telling them apart
  • Solar System

Part 1 of 6Stars

Stars
Stars huge balls of gas that give out light.
  • Most of the millions of dots of light in the night sky are stars.
Own light
  • Own light stars are the only objects in the night sky that continuously give out light.
Fixed arrangement
  • Fixed arrangement we always see the stars in the same arrangement, grouped into constellations, while other objects appear to move against the stars.
Twinkling
  • Twinkling a star appears to twinkle because its light changes direction as it travels through the Earth's atmosphere, not because the star's light is not constant.
Distance
  • Distance the Sun is the closest star, the other stars are very much further away, and their distances are measured in light-years.

Part 2 of 6Planets

Planets
Planets
  • Planets the name means "wanderers", given by ancient astronomers because they move against the stars.
Properties
  • Properties planets are not stars: they are objects in orbit around stars, made of rock or gas, and they do not give out their own light.
  • You see planets because light is reflected off them into your eyes.
Seen without a telescope
  • Mercury, Venus, Mars, Jupiter and Saturn.
Other planets
  • Uranus and Neptune.
Telling them apart
  • Telling them apart planets look like tiny discs and usually shine with steadier light than twinkling stars,
    • and they change position against the stars over several nights.
Solar System
  • Solar System the planets and other objects orbiting the Sun make up our Solar System.
Asteroid belt
  • Asteroid belt it lies between Mars and Jupiter and contains much smaller pieces of rock and one dwarf planet,
    • and Pluto is another dwarf planet much further from the Sun.
Exoplanets
  • Exoplanets planets that orbit other stars, and astronomers have found lots of them.

Part 3 of 6Moons

Moon
Moon an object that orbits a planet, sometimes called a natural satellite.
Earth's Moon
  • Earth's Moon the Earth has only one moon, made of rock, and it is the only object beyond the Earth that a person has set foot on.
Other planets
  • Other planets most have their own moons, which cannot be seen without a telescope, and Saturn has over 60 moons.
  • Phobos and Deimos, the moons of Mars, are not spherical.
Size
  • Size moons are not always small, and Titan, one of Saturn's moons, is bigger than the planet Mercury.
Difference from a planet
  • Difference from a planet a moon orbits a planet, whereas a planet orbits a star such as the Sun.

Part 4 of 6Comets

Comet
Comet a big, dirty snowball of ice and dust orbiting the Sun.
  • As it gets nearer to the Sun it produces a tail that makes a spectacular sight in the sky.
Name
  • Name it comes from the Greek for "hairy star".
Seen by reflection
  • Seen by reflection we see comets because, like planets and moons, they reflect sunlight.
Returning
  • Returning comets seem to appear out of nowhere and disappear, and ancient people thought they were a bad omen.
  • Once astronomers made measurements they realised that some comets return again and again, such as Comet Encke every three years,
    • while others return after hundreds or thousands of years.

Part 5 of 6Meteors and satellites

Shooting stars
  • Shooting stars streaks of light in the night sky are called "shooting stars", but they are not stars.
Meteor
  • Meteor a particle of dust or a piece of rock that burns up when it enters the Earth's atmosphere.
Meteorite
  • Meteorite a piece of rock that survives to reach the ground.
  • Tiny meteorites hit the Earth all the time, and about a dozen land on you every hour if you go outside.
Meteor shower
  • Meteor shower it is seen when the Earth moves through the dust left by a comet.
Artificial satellites
  • Artificial satellites there are thousands in orbit around the Earth.
  • Many are part of the global positioning system (GPS), which pinpoints positions on Earth using signals from many satellites.
  • You can see them near dawn or dusk when they reflect light from the Sun, and the brightest is the International Space Station.

Part 6 of 6What orbits what

ObjectOrbits
Planets, asteroids, comets, dwarf planetsThe Sun
Moon, artificial satellitesThe Earth
TitanSaturn
  • Seen by reflected light
    • planets, moons, comets and satellites are seen only because they reflect light from the Sun.

Key terms

TermMeaning
Stara huge ball of gas that gives out light.
Planeta large object that orbits a star and does not give out its own light.
Moona natural satellite orbiting a planet.
Cometa body of ice and dust orbiting the Sun that grows a tail near it.
Meteoritea piece of rock from space that reaches the ground.
Artificial satellitea human-made object orbiting the Earth.

Avoid these mistakes

1
Thinking planets give out their own light — they reflect sunlight.
2
Thinking shooting stars are stars — they are meteors burning up in the atmosphere.
3
Thinking Titan is a planet because it is large — it orbits Saturn, so it is a moon.
4
Thinking comets only appear once — many return.

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