What produces the striking red, blue, and black colors of ...

[cookcarl]

What produces the striking red, blue, and black colors of ionization nebulae?
 
  What will be an ideal response?

Question 2

The rate of cratering in the lunar highlands shows us that
 
  A) they must be younger than the older, darker mare.
  B) most of the asteroids must have hit the Moon, not the Earth.
  C) they range from 4.6 - 4.4 billion years old, on average.
  D) the largest impacts are the youngest, such as Copernicus and Tycho.
  E) the oldest rocks are at least as old as the mare, but some craters are much younger.

[bubulittle310@msn.cn]

Answer to Question 1

The bright red color is produced by an emission line of hydrogen in which the electron falls from energy level 3 to energy level 2. Starlight reflected from dust grains produces the blue colors, because interstellar dust grains scatter blue light more effectively than red light. The black regions are dark, dense gas clouds that block our view of the stars beyond them.

Answer to Question 2

C

[cookcarl]

Excellent

[tranoy]

Gracias!