A first quarter moon occurs when the Moon is about 90 degrees away from the Sun in its orbit around Earth. This happens approximately seven days after the new moon.

Here's a breakdown:

* New Moon: The Moon is between the Earth and the Sun. We can't see the Moon because the sunlit side is facing away from us.

* First Quarter: The Moon has moved a quarter of the way around its orbit and now shows a half-lit crescent shape.

* Full Moon: The Moon is on the opposite side of Earth from the Sun. We see the entire sunlit side of the Moon.

* Third Quarter: The Moon is three-quarters of the way through its orbit. We again see a half-lit crescent, but this time the lit side is on the right.

The exact timing of a first quarter moon can vary slightly due to the Moon's elliptical orbit and the Earth's own movement. However, it generally happens about a week after the new moon.