CHAPTER 3

THE EXPANDING UNIVERSE

If one looks at the sky on a clear, moonless night,

the brightest objects one sees are likely to be the planets Venus,

Mars, Jupiter, and Saturn. There will also be a very large number of stars,

which are just like our own sun but much farther from us.

Some of these fixed stars do, in fact,

appear to change very slightly their positions relative to each other as the earth orbits around the sun:

they are not really fixed at all! This is because they are comparatively near to us.

As the earth goes round the sun, we see them from different positions against the background of more distant stars.