What is the approximate temperature and what factors cause this variation?
Temperatures on the Moon vary between extremes of 120 °C during the lunar day and -150 °C during the lunar night. Some craters near the poles have areas that are in permanent shadow, these can reach temperatures down to -247 °C.
The moon does not have a permanent "dark side". The moon rotates on its axis once every 28 days, so every part of the moon has a day-and-night pattern. The American expression "the dark side of the Moon" refers to the far side of the moon, which we never see from Earth.
The temperature range is so different from Earth due to these factors:
- the Moon has no atmosphere. Earth's atmosphere reflects some of the Sun's energy during the day and traps the heat during the night.
- the slow rotation results in very long days and nights, i.e. a long period of uninterrupted heating followed by a long period of uninterrupted cooling.
- The moon consists mostly of rock with a low heat capacity, which will heat up and cool down quickly. Earth's oceans have a high heat capacity, so they take much longer to heat up.
As on Earth, the surface temperature changes with the latitude.
The temperature below the Moon's surface quickly stabilizes. According to this link, only a meter below the surface, the temperature is a constant -35 °C. Note that this contradicts the previous link, which says that the subsurface temperature also changes with the latitude.