Notes: Ch.-1.3 Spaceship Earth

How is Earth moving in our solar system?

• Earth rotates around its axis once everyday. 
• (moves in several ways, at surprisingly fast speeds..... we are NOT 'standing still')
• Earth orbits the Sun (revolves) one every year...
• at an average distance of 1AU ≈ 150 million KM
• with Earth's axis tilted by 23.5° (pointing to Polaris)
• it also rotates in same direction it orbits, counterclockwise as viewed from above North Pole 

• Our Sun moves randomly relative to the other stars in the local solar neighborhood
• at typical relative speeds of more than 70,000 KM/HR 
• stars are so far away, we cannot easily notice their motion
• it orbits the galaxy every 230 million years

• Most of Milky Way's light comes from disk and bulge..... but most of the mass is in its halo!

How do galaxies move within the universe?

• Galaxies are carried along with the expansion of the universe.
• Hubble discovered that: 
• all galaxies outside our Local Group are moving away from us.
• the more distant they are, the faster they are moving
• our universe is constantly expanding

Are we ever 'standing still?'

• NO!