Transcript Why does the sky move?

There are actually two different reasons why stars appear to move across our sky.
The first is because the Earth is spinning and second because the Earth itself is moving
around the Sun.
What they are
• As the Earth spins around, the stars
appear to move from east to west across
the sky. If a long exposure camera is left
facing the sky, there will be trails of light
across the photograph, known as star
trails.
Star images produced by a camera lens are point sources of
light of widely varying intensity scattered over the film. Normally,
no single photographic exposure on colour film can capture their
subtle colours. Those stars whose intensity is just right for their
colour to be recorded appear insignificant on the photograph,
while anything brighter is bigger, but is overexposed and appears
washed out.
Star trails around the
celestial poles
 As the Earth travels around the sun (once a year), it is
as if we are sitting on a Waltzer ride at the funfair. If
the whole Waltzer moved around on its track with the
cars not spinning, we would see everything around the
ride appear to be sweeping past once with every
revolution. Standing on the surface of Earth, as it
makes its journey around the Sun we see the stars
passing by until after a whole revolution around the
Sun, taking a year, we will have seen all the stars pass
by.
 If the waltzer had no roof, the sky overhead would
appear to be spinning around a point directly above
the car. This area of sky would always be visible to us
no matter where the car was on the track. This is the
same for the stars around the north star Polaris.
Because Polaris is close to the point in the sky directly
above the axis of spin of the Earth (the north pole) it is
always visible. The stars within 40 degrees of Polaris
appear to rotate around it and do not set below the
horizon, these stars are said to be ‘circumpolar’. Stars
further than 40 degrees from Polaris disappear below
the horizon for part of the year and reappear at the
same time every year.