The coolest white-dwarf: Surveys have been carried out to ...

[geoffrey]

The coolest white-dwarf: Surveys have been carried out to identify isolated white-dwarfs throughout the galaxy and its globular clusters.
 
  They have been found to span a range of temperatures, with a sharp lower limit of about 3000 K (i.e. many have been found at all temperatures from 10s of thousands of Kelvin down to 3000K, but none cooler). What does this observation reveal about the age of our galaxy?

Question 2

We are measuring the spectra of two hydrogen gas clouds. The laboratory frame wavelength of one hydrogen line is 656.2 nm. Cloud A's emission line wavelength is 660.1 nm and Cloud B's emission line wavelength is 670.1 nm.
 
  What can we conclude about these clouds?
  A) They are both approaching us, and Cloud A is approaching faster than Cloud B.
  B) They are both receding from us, and Cloud B is receding faster than Cloud A.
  C) They are both approaching us, and Cloud B is approaching faster than Cloud A.
  D) They are both receding from us, and Cloud A is receding faster than Cloud B.

[Zack0mack0101@yahoo.com]

Answer to Question 1

The galaxy has a finite age, when enough gas must have become present to generate stars which could go on to become white dwarfs. (This observation is one of the supporting pieces of evidence for the approximately 13 billion year age of the universe  the coolest observed white dwarfs are about 10 billion years old)

Answer to Question 2

B

[geoffrey]

Thanks for the timely response, appreciate it

[juliaf]

YES! Correct, THANKS for helping me on my review