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10.1Chapter 10: The Earth in Space (Galaxies and Asteroids)

Galaxies — Alhussan Physics - Stage 8 Revision Notes & Topical Questions

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📚 Alhussan Physics - Stage 8 Hub / Topical Revision
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Lesson summary

Physics 10.1 Galaxies — The Milky Way, Spiral, Elliptical and Irregular Galaxies — Alhussan International Academy — Physics (Stages 7–9) notes: Describe what is in a galaxy and what is in the Universe.Voyager probes — Voyager 1 and 2 were launched in 1977; Voyager 1 passed Jupite…

  • Oort cloud
  • Still in the galaxy
  • Planetary systems
  • Dust and gas
  • Band of stars
  • Position of the Sun

Section 1 of 8Leaving the Solar System

Leaving the Solar System
Voyager probes
  • Voyager 1 and 2 were launched in 1977; Voyager 1 passed Jupiter in 1979.
  • Both have passed through the Kuiper belt, the rocks and dust beyond Neptune.
  • Voyager 1 is about 23 billion kilometres away, further than anything else made by humans.
Oort cloud
  • Both probes will spend over 10 000 years travelling through objects weakly held by the gravity of the distant Sun.
Still in the galaxy
  • When they leave the Oort cloud they will still be inside the Milky Way.

Section 2 of 8What a galaxy is

What a galaxy is
Galaxy
Galaxy a huge group of stars, planetary systems, dust and gas held together by gravity.
Stars
  • Usually thousands of millions of them.
Planetary systems
  • Astronomers think most stars have planets.
Dust and gas
  • From stars that have exploded or left over from the formation of the Universe.
Number
  • Our galaxy is one of thousands of millions of galaxies in the Universe.

Section 3 of 8The Milky Way

Name
  • "Galaxy" comes from the Greek word for "milky".
Band of stars
  • From a dark place we see a hazy white band, which is the concentration of stars seen when looking along the disc.
  • Most stars we can see are in the Milky Way.
Shape
  • It is a spiral galaxy, a disc with curved arms and a bulge in the middle.
  • Images of the disc are models worked out from telescope observations, not photographs taken from inside.
Centre
  • Astronomers think the Sun and other stars orbit a huge black hole at the centre.
Position of the Sun
  • The Sun is in one of the arms, about two thirds of the way out, and takes about 230 million years to orbit the centre once.

Section 4 of 8Nearest star

Proxima Centauri
  • The nearest star to the Sun, with a diameter seven times smaller than the Sun's.
Exoplanet
  • At least one exoplanet orbits it, making it our nearest other solar system.
Distance
  • Light from the Sun takes about 8 minutes to reach us, but light from Proxima Centauri takes over four years.

Section 5 of 8Other galaxies

  • Visible galaxies
    • Some bright fuzzy objects in the night sky are galaxies beyond the Milky Way, and a telescope is needed to see detail.
    • Andromeda is the nearest spiral galaxy to our own.
    • The Large and Small Magellanic Clouds are neighbouring galaxies.
TypeShape
SpiralFlat disc with curved arms around a central bulge (the Milky Way)
EllipticalRounded or oval ball of stars
IrregularNo regular shape

Section 6 of 8The Universe

Universe
Universe everything that exists, including all stars, planets, moons, comets, asteroids and meteors.
Size
  • We do not know how large the Universe is or whether it is infinite.
Observable distance
  • We can see for 13.7 billion light years in all directions.
Outside
  • Science cannot answer what is outside the Universe because there may be no outside.

Section 7 of 8Key terms

TermMeaning
GalaxyA huge group of stars, planetary systems, dust and gas held together by gravity.
Milky WayThe spiral galaxy that contains our Solar System.
UniverseEverything that exists.
Kuiper beltThe rocks and dust beyond Neptune.
Oort cloudA region of distant objects weakly held by the Sun's gravity.
Black holeA very dense object, thought to be at the centre of the Milky Way.

Section 8 of 8Exam technique

1
Thinking the Solar System and a galaxy are the same — a solar system is one star with its planets and a galaxy contains thousands of millions of stars.
2
Thinking all stars in the sky are in other galaxies — most visible stars are in the Milky Way.
3
Thinking the Milky Way images are photographs — they are models.
4
Thinking the Voyager probes have left the galaxy — they are still inside the Milky Way.

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