The Moon's shapes

At night, the Moon appears to be the biggest object in the sky. Your book, Our Wondrous World (Chapter 10), says that the shape of the Moon looks different on different nights.

On some nights, the Moon is a complete circle. This is called Poornima, or the full Moon. On some nights, it is a thin curved shape, like the letter 'C'. On other nights, it looks as if it has been cut down the middle, like half a circle.

And there are nights when the Moon cannot be seen at all. This is called Amavasya, or the new Moon. It does not happen just once: it comes again and again, after the same number of days.

Because the Moon's shapes come back in the same order, people from ancient cultures used them to keep count of the days. This gave us the earliest calendars.