Charon is not a moon of Earth, but a moon of Pluto. And while it's true that Charon is tidally locked to Pluto, meaning one side always faces Pluto, neither the far side of Charon nor the far side of Pluto is permanently dark.

Here's why:

* Pluto and Charon orbit each other. This means that both celestial bodies are constantly rotating around a common center of mass.

* The far side of both Pluto and Charon get sunlight. As they orbit each other, their far sides are illuminated by the Sun for half of their orbital period.

However, it's worth noting that:

* Pluto and Charon are very far from the Sun. So, even when the far side faces the Sun, it's still much dimmer than on Earth.

* The far side of Charon likely experiences very long periods of darkness. The orbital period of Pluto and Charon is about 6.4 Earth days, so the far side of Charon spends about 3.2 days in the shadow of Pluto.

So, the far side of Charon isn't constantly dark, but it does experience long periods of darkness and very dim sunlight compared to Earth.