Chhavi says the Moon seems to change shape through the month because, as it travels around the…

Why

Bilal's idea is one of the most common in the world, and it isn't unreasonable: the Earth does cast a shadow, and the Moon does seem to darken. But the phases aren't caused by that shadow. The Sun always lights up one half of the Moon, just as it lights up one half of the Earth. As the Moon travels around the Earth over about a month, we look at that lit half from different angles: sometimes we face it fully (full moon), sometimes from the side (half moon), and sometimes almost entirely from behind (new moon). The Earth's shadow falls on the Moon only during a lunar eclipse, which is much rarer. Test: around the half-moon phase you can often see the Moon in the afternoon sky while the Sun is also up — the Earth is clearly not between them then, so its shadow can't be what hides half the Moon. Chhavi is right: the phases come from how much of the Moon's sunlit half we can see as it goes around the Earth.