We can find out lots of things about stars and galaxies by studying the
light from them. We can use a prism to split the light into a spectrum. The
wavelength of light increases across the spectrum from blue to red. We
can tell from the spectrum if a star or galaxy is moving towards or away
from us. This is because:
- the light waves are stretched out if the star or galaxy is
moving away from us. We call this red shift because the
spectrum of light is shifted towards the red part of the
spectrum
- the light waves are squashed together if the
star or galaxy is moving towards us. We call this
blue shift because the spectrum of light is shifted
towards the blue part of the spectrum
The faster a star or galaxy is moving towards
or away from us, the bigger the shift is
Red shifts and blue shifts follow
the Doppler effect
Red shift and blue shift show that all galaxies are moving
away from each other, proving that the whole universe is
expanding
The big band theory
The Big Bang Theory tries to explain the expanding Universe. It states:
- the Universe is expanding after
exploding suddenly in a Big
Bang from a very small initial
point
- space, time and matter were
created in the Big Bang
In 1965, it was discovered that
microwaves were coming from every
direction in space. The existence of
this background microwave radiation
can only be explained by the Big Bang
Theory