Which region of the ionosphere disappears completely at night? Which region is permanent?
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## Question 1.8.1
1. What is the ionosphere made of?
When intense sunlight hits the upper atmosphere, the atoms there absorb so much energy that electrons are ejected from their orbits around the atom. As a result, the atoms become a sea of ions and free electrons known as the __ionosphere__.
## Question 1.8.2
2. Which region of the ionosphere disappears completely at night? Which region is permanent?
The D-region is made of ions that completely recombine overnight. This region extends from about 50 to 90 km (31 to 56 miles).
The F-region is the permanent region of the ionosphere that extends upwards from 150 km (93 miles). The region is not significantly diminished at night.