Explain how we can estimate that there are about 50-100 billion ...

[justinmsk]

Explain how we can estimate that there are about 50-100 billion galaxies in the observable universe.
 
  What will be an ideal response?

Question 2

Which statement is true of Venus' surface?
 
  A) There are no shield volcanoes.
  B) Atmospheric pressure is very low.
  C) It has remained unchanged for billions of years.
  D) There is an extensive hydrosphere.
  E) There are two continent sized uplands.

[yahahah24021]

Answer to Question 1

While it's impossible to count so many galaxies one by one, we can observe a small part of the sky in detail and then extrapolate to get the total number. As an example, the Hubble deep field shows thousands of galaxies in a very small angular patch in the sky (about equal to the size of a grain of sand held at arm's length). Multiplying the number of galaxies by the ratio of the angular area of the entire sky to the angular area of the deep field then gives an estimate of the total number of galaxies in the observable universe.

Answer to Question 2

C

[justinmsk]

Gracias!

[Joy Chen]

Great answer, keep it coming