Moses found difficulty with the renewal of the moon… G-d therefore showed him with His finger the moon in the sky and said to him, ‘You will see a moon like this and you will then sanctify [the month].’

Why did Moses have a problem with the moon’s renewal?

And what did G-d show him? If there was a moon in the sky, Moses could have looked up and seen it on his own. And if there was no moon yet – which is more likely because the new moon was just being born – what exactly did G-d show him? How can a new moon be seen with the naked eye?”