Chapter 32, Problem 9RQ

Why are days on Mercury very hot and nights very cold?

To determine

The reason for very hot days and cold nights on the Mercury.

Answer to Problem 9RQ

The day on the Mercury is very hot due to its least distance from the Sun and nights are very cold due to absence of atmosphere on the Mercury.

Explanation of Solution

The distance of Mercury to the Sun is least. The period of revolution of the Mercury about the Sun is least then other planets and the Mercury takes only $88\text{ days}$ to complete one revolution around the Sun.

The Mercury spins about own axis only three times for every two revolutions about the Sun. This makes the daytime very long. The Mercury receives large solar radiation, so the temperature of Mercury becomes very high and days at Mercury become very hot.

There is a very high vacuum on Mercury due to the absence of atmosphere, so heat it receives at daytime lose rapidly. The temperature at the Mercury becomes very low because of high rate of heat loss due to the absence of atmosphere.

Conclusion:

Therefore, the day on the Mercury is very hot due to its least distance from the Sun and nights are very cold due to absence of atmosphere on the Mercury.