What does "a new moon" mean? (Roald Dahl)?

I am reading "Danny - The Champion of the World" by Roald Dahl in German translation and came across a weird passage. I suspected it to be a translation error as it is nonsensical in the German translation.

There it says that it was new moon (Neumond) and a field is lit by moonlight. In German, Neumond specifically means the moon phase when the moon is not visible at all (as opposed to Vollmond - full moon), and of course when there is Neumond there cannot be moonlight.

I found the original passage in Amazon's Look Inside function and there it reads:

"There was a new moon in the sky and across the road the big field lay pale and deserted in the moonlight."

The moonlight is mentioned as is "a new moon".

Now, I'm wondering is this an error that RD made or does the indefinite article "a" change the meaning?

If so, what does "there was a new moon in the sky" mean?

Thank you! :-)

Zac