Heliocodex

Learn / Lesson packs

Space in ten lessons

The shortest way round the whole subject. Ten first looks, from how big it all is to how it began, each needing nothing but curiosity.

10 lessons in 4 parts. Every one can be read again at a deeper level.

Begin with lesson 1

The blue and white Earth, half lit, above the grey horizon of the Moon.
A photograph. Earthrise: the Earth seen from the Moon by the crew of Apollo 8 on 24 December 1968. Credit: NASA / Bill Anders.

Part 1

Where we are

The size of things, and the two ideas that explain why anything moves the way it does.

  1. 1
    How big is space

    The true spacing of the Solar System and the stars, on a scale you can walk.

    With moving pictures and photographs

  2. 2
    What gravity is

    Everything pulls on everything else. The pull grows with mass and fades with distance, and it never quite reaches zero.

    With moving pictures and photographs

  3. 3
    What an orbit is

    An orbit is a fall that never reaches the ground. Newton's cannonball shows how.

    With moving pictures and photographs

Part 2

Our own corner

The Sun and what goes round it.

  1. 4
    What the Sun is

    The Sun is a star seen close up: a ball of glowing gas, layered like an onion, with a furnace in the middle.

    With moving pictures and photographs

  2. 5
    Rock, gas, ice: three kinds of planet

    The eight planets come in three sorts, and where each one formed explains which sort it is.

  3. 6
    What a moon is

    Anything that orbits a planet is a moon. There are more than 400, from worlds bigger than Mercury to rocks a kilometre across.

Part 3

The stars

What the points of light are, and what becomes of them.

  1. 7
    What a star is

    A star is a ball of gas heavy enough to light its own fire. How heavy it is decides almost everything else about it.

    With moving pictures and photographs

  2. 8
    How stars live and die

    Stars form in clouds of gas, shine steadily for most of their lives, and end as white dwarfs or in explosions, depending on their mass.

    With moving pictures and photographs

Part 4

Everything else

Our galaxy, and the universe it is one small part of.

  1. 9
    The Milky Way

    Our galaxy is a flat, turning disc of a few hundred billion stars. We live inside it, about half way out, and have never seen it from outside.

  2. 10
    The expanding universe

    Distant galaxies are all moving away from us, and from each other. Run the film backwards and you arrive at a hot, dense beginning 13.8 billion years ago.

Go and look