Measurement Review

Question 1

Astronomical Unit (AU)

Answer 1

• Average Distance between the Earth and the Sun
• (150 million kilometers = 93 million miles)

Question 2

Light-year (ly)

Answer 2

• The distance that light can travel in 1 year
• A disatnce measurement, not a time measurement
• About 10 trillion kilometers (6 trillion miles)
  -Light travels at a finite speed (300,000 km/s)

1 light-year = (speed of light) x (1 year)

Question 3

Seeing in the Past

Answer 3

Moon = 1 second
Sun = 8 minutes
Sirius = 8 years
Andromeda Galaxy = 2.5 million years

-Thus, we see objects as they were in the past
-The farther away we look in distance, the further back we look in time

We see a galaxy 7 billion light-years away as it was 7 billion years ago when the universe was about hald its current age of 14 billion years (we see it when its 7 billion years when the universe is much younger)
At 12 billion light-years awat, the galaxy we see existed when the universe was only about 2 billion years old. (14-12=2)
At 14 billion we see the universe shortly after big bang, before galaxies existed
We cannot see anything sarther than 14 billion light years away. That is the observable universe