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?