Author Question: What color is an H I region? A) red from ionized hydrogen's alpha transition, such as in the ... (Read 87 times)

serike · **on:** Jul 27, 2018

What color is an H I region?

A) red from ionized hydrogen's alpha transition, such as in the Orion Nebula
B) red from reddening due to dust
C) colorless; it emits in the radio region
D) blue from the scattering of light off the tiny atoms, such as around the Pleiades
E) blue from ionized helium's alpha transition, such as the Horsehead Nebula

Question 2

How is the geometrical structure of the universe today related to the presence of matter in the universe? How is this related to the future history of the universe?

What will be an ideal response?

huda · **Reply #1 on:** Jul 27, 2018

Answer to Question 1

C

Answer to Question 2

The geometrical structure of the universe has positive curvature (closed, as with a sphere), negative curvature (open, as with a saddle shape), or is flat. This depends on whether the density of the universe is above, below, or exactly at critical. If above, the universe will eventually collapse back on itself. If below, the universe will expand forever. If critical, the universe will brake to an exact halt after an infinite amount of time.