Understanding the Moon Phases: From New Moon to Waning Crescent

How Moon phases arise

The Moon does not shine on its own. The Sun always lights exactly one half of the lunar sphere, and depending on where the Moon is in its orbit around Earth, we see a larger or smaller part of that bright half. When the Moon lies between Earth and the Sun, its unlit side faces us – that is the New Moon. When it stands opposite the Sun, we look at the fully lit side – that is the Full Moon. In between lie all the stages from a slim crescent to an almost round disk.

On average, 29.53 days pass from one New Moon to the next, the so-called synodic month. It is a little more than two days longer than one orbit of the Moon relative to the stars (27.32 days), because Earth moves along its own orbit around the Sun during that time and the Moon has to make up the difference. The phase is the same everywhere on Earth at the same moment – only the orientation of the crescent differs between the Northern and Southern Hemispheres.

The eight Moon phases at a glance

Astronomically there are four principal phases, each marking a precise moment: New Moon, first quarter, Full Moon and last quarter. Between them lie four intermediate phases that each last several days. Together they make up the eight phases that many lunar calendars and astrological readings work with. On average, the first quarter is reached after a little more than seven days, the Full Moon after almost 15 days and the last quarter after about 22 days.

The table shows how the phases are distributed over the angle between the Moon and the Sun, when you can typically see the Moon and which theme astrology symbolically connects with each phase. The visibility notes apply roughly to mid-northern latitudes. Because the Moon moves at varying speeds along its elliptical orbit, the transitions shift slightly from month to month.

New Moon and Full Moon: the two turning points

At New Moon, the Moon appears close to the Sun as seen from Earth and rises and sets roughly with it – which is why it is practically invisible. Only one or two days later does the first slim crescent appear in the evening sky. At Full Moon, it stands opposite the Sun: it rises around sunset, is highest around midnight and sets at sunrise.

Eclipses are only possible at these two moments: a solar eclipse at New Moon and a lunar eclipse at Full Moon. They do not happen every month because the Moon's orbit is tilted by a little more than five degrees relative to Earth's orbit. Only when a New or Full Moon falls near the points where the two orbits intersect, the lunar nodes, do the Sun, Earth and Moon line up closely enough. Such eclipse seasons occur about twice a year.

Waxing or waning? How to tell the phase

In the waxing half of the cycle, the lit part grows from evening to evening, and the Moon is mainly visible in the first half of the night. In the waning half, the light shrinks again and the Moon appears later and later in the night until it is only visible in the morning sky. The half Moons of the first and last quarter mark the middle of each half.

In the Northern Hemisphere, a simple rule applies: if the right side is bright, the Moon is waxing; if the left side is bright, it is waning. In the Southern Hemisphere it is the other way around. With a slim crescent it is worth taking a closer look, because the unlit part is often faintly visible too. This earthshine occurs because Earth reflects sunlight and adds a little light to the Moon.

Moon phases in astrology

In astrology, the Moon stands for feelings, needs and rhythms. Its cycle is therefore often read as an image for processes: at the New Moon something is planted, in the waxing phase it grows, at the Full Moon it becomes visible, and in the waning phase it is processed and released. In the 20th century, the astrologer Dane Rudhyar described this lunation cycle as a psychological model of development that many modern interpretations refer to.

These interpretations are symbolic. They can be a prompt for self-reflection but do not replace decisions based on facts, conversations or professional advice. If you would like to work with the lunar cycle, you could use it like this, for example:

• New Moon: write down a plan or a question you want to carry through the coming month.
• First quarter: consider which concrete next step moves your plan forward.
• Full Moon: note what has become visible – progress as well as tension.
• Last quarter: decide what you want to keep and what you want to bring to a close.

How Stellune calculates the Moon phase

For every daily edition, Stellune calculates the positions of the Sun, Moon, Mercury, Venus, Mars, Jupiter and Saturn for 12:00 UTC on that day. It uses the open-source library Astronomy Engine. The Moon phase follows from the angle between the Moon and the Sun: 0 degrees corresponds to the New Moon, 90 degrees to the first quarter, 180 degrees to the Full Moon and 270 degrees to the last quarter.

Stellune divides the full circle into eight equal sections of 45 degrees, each centered on one phase – which gives the values in the table above. You can see the resulting phase on every horoscope page. It also feeds into the daily themes as a weighting: a waxing Moon emphasizes activating impulses, a waning Moon emphasizes reflection and completion.

Myths and facts about the Moon