Of the following, which of the following is the largest object? ...

[DelorasTo]

Of the following, which of the following is the largest object?
 
  a. the Milky Way galaxy
  b. the Large Magellanic Cloud
  c. the Local Group
  d. the Andromeda galaxy

Question 2

What observations demonstrate the existence of an interstellar medium?
 
  What will be an ideal response?

[vseab]

Answer to Question 1

c

Answer to Question 2

One way to investigate properties of the ISM is to measure its effects on the starlight that passes through it. Astronomers observe that distant stars appear fainter than they should for their distances and luminosities, an effect called interstellar extinction. Distant stars also appear redder than they should for their spectral types, an effect called interstellar reddening. Astronomers also observe interstellar absorption lines in the spectra of stars. Lines that cannot be produced in stars must be produced by atoms located between the stars and Earth.