Simple Science
Why is the sky blue?
© Linda Åslund 1
At a glance
Sunlight travelling
through the atmosphere
is scattered by gases and
particles
During the Day
Sunlight is travelling over
our head through the
atmosphere
Sunlight is a mix of different coloured
light. We can see these colours if we
shine sunlight through a prism or if we
look at the reflective side of a CD.
As sunlight travels through the
atmosphere, it is scattered by gases
and particles. Different colours of light
are scattered by different amounts.
Blue light is scattered far more than
red light.
Blue light is scattered
more than any other
colour so we see more
blue light
During Sunrise and
Sunset
Sunlight is travelling
through the atmosphere
towards us
The sun is low in the sky
so blue light is scattered
away from us leaving
more red light
The sky looks red
During the day, the sun is high in
the sky and a lot of sunlight is
travelling through the
atmosphere far above the
ground.
During the sunrise and sunset,
the sun is low in the sky and a lot
of sunlight is travelling through
the atmosphere close to the
ground.
Red light travelling through the
high atmosphere is not
scattered very much and
continues on through the
atmosphere. However, blue light
is scattered in every direction.
This means a lot of blue light
reaches the ground causing the
sky to look blue.
As before, the blue light is
scattered far more than the red
light. Since the sun is now far
lower in the sky, by the time the
light reaches us, the blue light
has been scattered so that very
little remains. The red light has
not been scattered as much and
so the sky looks red.
Centre for Lifelong Learning
Alex Brown, 2012
1