Author Question: The nights are cold on Mercury because it has a negligible atmosphere. a. True b. False ... (Read 48 times)

futuristic · **on:** Jul 27, 2018

The nights are cold on Mercury because it has a negligible atmosphere.

a. True
b. False
Indicate whether the statement is true or false

Question 2

Why do Cepheids pulsate?

What will be an ideal response?

Expo · **Reply #1 on:** Jul 27, 2018

Answer to Question 1

True

Answer to Question 2

Studies using stellar models show that variable stars in the instability strip pulsate like beating hearts because of an energy-absorbing layer in their outer envelopes. This layer is the region where helium is partially ionized. Above this layer, the temperature is too low to ionize helium, and below the layer it is hot enough to ionize all of the helium. Like a spring, the helium ionization zone can absorb energy when it is compressed, and release it when the zone expands, and that is enough to keep the star pulsating.