Why temperature of dark side of moon is not 3 Kelvin

The temperature of the space between Earth and the Moon is around 3 Kelvin ($$\approx -270^\circ {\rm C}$$). The moon has no atmosphere, therefore the heat convection is not possible from the bright side to the dark side on Moon.

Now, if the temperature of the space around the moon is $$3 {\rm K}$$, then how the dark side of the moon is having a temperature of $$100 {\rm K}$$?

References

• The temperature of (gas in) space between the Earth and the Moon is not 3 K; even the first of your links (which does misleadingly claim that "empty interstellar space" has a temperature of 3 K) doesn't say that. – Peter Erwin Mar 31 at 10:41

In other words: During (lunar) day, the Sun heats up the surface of the Moon and it gets pretty warm, even on the (not so) "dark" side of Moon. This explains the $$100 {\rm K}$$ you are citing.