Notes: Ch.-1.2 The Scale of the Universe

How big is Earth compared to our solar system?

• Let's reduce the size of the solar system by a factor of 10 billion; the sun is now the size of a large grapefruit (14 CM diameter)

How big is Earth on this scale?

• B. A tip of a ballpoint pen (15 meters away)

How far away are the stars?

• On our 1-to-10 billion scale, it's just a few minutes' walk to Pluto. On the same scale, stars are thousands of kilometers away.

How far would you have to walk to reach Alpha Centauri? 

• D. The distance across the United States (2500 miles)

How big is the Universe?

• The Milky Way is one of about 100 billion galaxies 
• 10¹¹ stars/galaxy X 10¹¹ galaxies = 10²² stars
• It has as many stars as dry grains of sand on ALL of Earth's beaches.

How do our lifetimes compare to the age of the Universe?

• The cosmic calendar: A scale on which we compress the history of the universe into one year.
•   14 billion light-years in radius

How big is the earth compared to our solar system? 

• On a scale of 1 to 10 billion, the sun is the size of a grapefruit. 
• Earth is the size of a tip of a ballpoint pen. (15 M away) 
• Distances between planets are huge compared to their sizes.

How far away are the stars? 

• (on same scale) Stars are thousands of kilometers away.