What form of seismic waves travel in compressions and ...

[bobbie]

What form of seismic waves travel in compressions and decompressions?
 
  a. systematic waves
  b. earthquake waves
  c. pressure waves
 d. shear waves
 e. gravity waves

Question 2

What observations indicate the presence of dust in the interstellar medium?
 
  What will be an ideal response?

[hollysheppard095]

Answer to Question 1

c

Answer to Question 2

The dust in the ISM makes distant stars appear fainter than they would if space were
perfectly transparent. This phenomenon is called interstellar extinction, and in the neighborhood of the Sun it amounts to about 1 magnitude per thousand parsecs (pc) at visual wavelengths.

The ISM dust also affects the colors of stars. That is the reason why extinction is more severe at shorter wavelengths, which makes stars look redder than they should be. Some hot but distant O stars, for instance, actually look red and not blue. This effect is called interstellar reddening.