Answer is:
hygrometer
Explanation:
hygrometer is used to measure humidity
Answer is:
extremely cool
Explanation:
at upper layer of atmosphere astronout feel extereme cold
Answer is:
geo-thermal energy
Explanation:
The energy that can harness heat stored below the earth's surface is known as geothermal energy
Answer is:
distance between source and observer
Explanation:
Doppler effect is independent of distance between source and observer