Why the Moon changes shape
The Moon does not make its own light. It reflects sunlight, and half of it is always lit. What changes is how much of that lit half we can see from Earth, which depends on the angle between the Sun, the Earth and the Moon as the Moon circles us.
A common mix-up is that the phases come from Earth's shadow falling on the Moon. They do not. Earth's shadow only reaches the Moon during a lunar eclipse, which is a separate and much rarer event.
The full cycle from one new moon to the next, called the synodic month, lasts about 29.5 days. That is why a full moon shows up roughly once a month, and why the date drifts earlier or later on the calendar.
The eight phases at a glance
Astronomers and skywatchers usually split the cycle into eight steps. Four are the headline moments: new moon, first quarter, full moon and last quarter. The four in between are the crescents and gibbous phases.
In the Northern Hemisphere, which covers the US, Canada and the UK, the lit side grows from the right while the Moon is waxing and shrinks from the right while it is waning. In the Southern Hemisphere, including Australia and New Zealand, the Moon appears flipped, so the lit edge sits on the left during the waxing half.
- New moon. The Moon sits between us and the Sun and its lit side faces away.
- Waxing crescent. A thin sliver appears and grows over the first week.
- First quarter. Half the disk is lit, about a week into the cycle.
- Waxing gibbous. More than half is lit and it is heading toward full.
- Full moon. The whole face is lit and the Moon rises near sunset.
- Waning gibbous. Slightly less than full and slowly shrinking.
- Last quarter. Half lit again, now on the opposite side.
- Waning crescent. A fading sliver in the early morning sky.
Moon rituals and what people make of them
Across many traditions people have used the Moon as a calendar and as a mirror. In modern spiritual practice, especially the WitchTok and journaling communities, the new moon is a time to set intentions and the full moon is a time to reflect and let go of what is no longer serving you.
These are cultural and symbolic practices, not science. There is no evidence that the Moon changes your luck, health or finances. Many people simply find that a monthly rhythm makes a good prompt to pause, write things down and check in with themselves, and that is plenty of reason to try it.
If you like the idea, keep it low-pressure. A notebook and ten quiet minutes work as well as anything elaborate, and a candle is optional. If you do use one, keep it away from curtains and never leave it burning unattended.
Full moon names and Blue Moons
In the US you will often hear full moons called by names such as Wolf Moon, Snow Moon, Harvest Moon and Hunter's Moon. These are traditional North American names, popularized by almanacs and partly drawn from Native American and early colonial sources. The exact origins vary from name to name.
A Blue Moon is not blue. The modern definition is a second full moon within one calendar month, which happens roughly every two to three years. An older seasonal definition counts the third full moon in a season that has four. A Supermoon is a full or new moon that happens when the Moon is near its closest point to Earth, so it looks a little larger and brighter. The difference is real but subtle.
Questions people ask
How often is there a full moon?
About every 29.5 days. Because a calendar month is slightly longer than that, most years have 12 full moons and some have 13.
Why does the Moon look different in Australia?
The Southern Hemisphere sees the Moon from the opposite side up, so a waxing crescent lights up on the left instead of the right. The Moon itself is the same everywhere. Only the viewing angle differs.
Do eclipses happen every month?
No. The Moon's orbit is tilted about 5 degrees relative to Earth's orbit around the Sun, so most months the shadows miss. Lunar eclipses can only happen at a full moon, and solar eclipses only at a new moon.
Does the Moon phase I was born under matter?
In astrology and in personal ritual, some people find the birth phase a meaningful symbol. Astronomically it is simply a fact about the sky that night, and it does not determine your personality.