The Night Sky
What are constellations?
Why do we see some in winter, some
in summer and some all year long?
Why do they move?
How are they useful?
Our Place in Space
• Earth does not
occupy any special
place in the Universe
• The Universe:
It is all of space and
everything in it…
including time.
1.3 The “Obvious” View
The most simplest
observation in Astronomy:
Look at the night sky
About 3000 stars visible at
any one time; distributed
randomly but human brain
tends to find patterns…
These patterns are
constellations
1.3 The “Obvious” View
Group stars into constellations:
figures having meaning to those
doing the grouping
Useful: Polaris, which is almost
due north
Not so useful: Astrology, which
makes predictions about
individuals based on the star
patterns at their birth
Why do we see some constellations in winter,
some in summer and some all year long?
• We need to understand
how the Earth moves
around our Sun.
• We see constellations
in 2 dimensions from
earth. Stars are
actually placed in 3D
1.3 The “Obvious” View
Stars that appear close in the sky may not actually be
close in space:
Why do the Stars Move?
Polaris –
the North Star
Circumpolar
Constellations?
Why do the Stars Move?
• The Stars don’t actually move…
It is the Earth that is moving
(spinning).
• The spinning Earth gives the
perception that the stars move.
• Polaris – Earth’s northern axis
points at this star so its
movement is not affected by
Earth’s Rotation.
How are Constellations Useful?
• Finding N, S, E & West
- Find Big Dipper… then
follow end stars over to
Polaris (the North Star)
• Track your position on
Earth (navigation)
• What about the 5
wanderers?