Moon Phases

When you look outside tonight, how will the moon look up in the sky? Which nights will be brightly lit by moonlight, and which will be dark? This image shows the kind of moon you might expect to see tonight - it has the moon in its proper phase.

Click on the date and time beneath the image, and change it to your local time!

The phases, or changing appearance, of the Moon depend on its position relative to the position of the Sun.

When the Moon is between the Sun and the Earth, the side of the Moon facing the Earth is dark. This is called a "new moon". As the Moon travels eastward in its orbit, more of its sunlit side becomes visible to Earth and the Moon is said to be "waxing". More specifically, the phase after a new moon is called a "waxing crescent" because we can see no more than a quarter of the Moon at this point.

As the Moon continues eastward, the Sun, Moon, and Earth form a 90 degree angle and the Moon appears half dark and half light to us here on Earth. This is a "first quarter" phase. After the first quarter phase, more than a quarter of the Moon is visible to us, so it is now in a "waxing gibbous" phase.

As the Moon continues its revolution around Earth, the Sun, Earth, and Moon align with the Earth in the middle. The side of the Moon facing Earth is now fully lit. This is called a "full moon" phase.

As the Moon travels further around in its orbit, the lit portion of the Moon visible to Earth becomes smaller, so the Moon is now said to be "waning" as it enters the next phase. After the "waning gibbous" phase, the Moon enters the "third quarter" phase where once again the Moon appears half dark and half light from Earth. As it completes its revolution around Earth, the Moon enters a "waning crescent" phase just prior to starting the cycle again as a new moon.