In this week's parsha, the final plagues are visited upon the Egyptians, and the Israelites are told: "this month shall be to you the head of the months; to you it shall be the first of the months of the year."
The Hebrew calendar is lunar, which is why the Jewish holidays are never on the same (English) date year to year. Since the celebration of Passover must happen in the spring, leap months are added to the calendar (seven times every nineteen years) to sync up the seasonal celebrations.
We mark the beginning of each new month at the new moon, and many of our holidays fall in the middle of the month, at the full moon. I genuinely enjoy watching the night skies in the weeks leading up to Passover to remind me how much time I have left to get ready for the holiday. As the moon grows and gets fuller, I have to plan faster!
It's a wonderful thing to make the time to look up at the stars and the moon with our children. Not only can we use the moon to track our holidays, but looking at up the celestial objects reminds us of the vastness of God's greatness. It gives us yet another reason to be thankful.