The Night Sky

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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?

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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.

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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
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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
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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

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1.3 The Obvious View
Stars that appear close in the sky may not
actually be close in space
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Why do the Stars Move?

• Polaris
• the North Star
• Circumpolar Constellations?

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Why do the Stars Move?

• The Stars dont actually move It is the Earth
  that is moving (spinning).
• The spinning Earth gives the perception that the
  stars move.
• Polaris Earths northern axis points at this
  star so its movement is not affected by Earths
  Rotation.

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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?