What Are the Moon’s Phases and Why Do They Matter?

Earth’s Moon, the planet’s only natural satellite, is so close that you can see some of its surface features with the naked eye—but only when it’s at least partially illuminated by the Sun. In this article, I’ll delve into the Moon’s phases, including why they occur and how they impact life on Earth.

Why Are There Moon Phases?

The Sun always lights up one half of our Moon. However, that’s not always the half we can see. Indeed, the amount of lunar illumination we can see depends on where the Moon is in its orbit around Earth. So, when we talk about Moon phases, we’re actually referring to where the Moon is compared to us and, thus, the Sun.

Think of it this way: When the Moon sits between the Sun and Earth, only the side facing away from us is lit up, meaning we can’t see it at all. This is a new moon. If the alignment is perfect, we may experience a solar eclipse, which is when parts of the Earth sit in the Moon’s shadow and darken momentarily. However, since the Moon has a tilted orbit, it usually passes slightly above or below that perfect line.

Then, as the Moon moves further east around Earth and away from the Sun, more of it becomes illuminated. As it reaches its halfway point around the orbit of the Earth, the Sun’s rays beam past Earth and light up the side of the Moon facing us. This is a full moon. Again, if the three bodies align perfectly, we may see a lunar eclipse, meaning Earth casts a shadow on the Moon.

The Moon travels around Earth every 27.3 days, though the Moon’s phase cycle takes 29.5 days due to the Earth’s simultaneous movements in space.

What Are the Eight Moon Phases?

You may have heard of the Moon being described as waxing and waning. The Moon is waxing when we can see more of its surface each night, and it’s waning when less of its surface is illuminated from our perspective on Earth.

However, there’s more to the Moon’s phases than simply being waxing or waning. In fact, there are eight phases in the Moon’s 29.5-day cycle:

Phase	Name	Description	Earth’s View
1	New moon	Only the side facing away from Earth is illuminated.
2	Waxing crescent	The side facing Earth appears as a thin sliver that gets broader each night.
3	First quarter	Half of the side facing Earth is illuminated on its way to full apparent illumination.
4	Waxing gibbous	More than half the side facing Earth is illuminated, and more of this side appears illuminated from Earth each night.
5	Full moon	The whole of the side facing Earth is illuminated.
6	Waning gibbous	More than half the side facing Earth is illuminated, but less of this side appears illuminated from Earth each night.
7	Third quarter	Half of the side facing Earth is illuminated on its way to 0% apparent illumination.
8	Waning crescent	The side facing Earth appears as a thin sliver that gets thinner each night.

Why Are the Moon Phases Important?

The Moon’s phases affect humans and nature in various ways.

For us, the Moon’s terminator—the line separating the satellite’s lit and shaded sides—is where features cast long shadows that make them clearer. This is because it’s the point at which sunlight strikes the Moon at its narrowest angle. As a result, if you’re looking at the Moon through binoculars or a telescope, while you might be tempted to do so during a full moon, you’ll appreciate the Moon’s craters much more during any of the partial illumination phases.

If you’re planning a night of stargazing, make sure you check which phase the Moon is currently at. For example, if you want to observe the Milky Way or fainter stars and galaxies, you’ll find this much more challenging when there’s a full moon above the horizon. Ideally, you’d want to wait until the Moon is in its new phase, or—at the very minimum—one of its crescent stages.

The Moon’s illumination is also crucial for wildlife, acting as a navigational tool for some nocturnal animals. These animals also use the moonlight to help them with hunting, though they need to watch their backs during the full moon phase, when they’re as susceptible as their prey to attack.

What’s more, other creatures can detect the difference between sunlight and moonlight, meaning they can find their way regardless of whether it’s night or day. Perhaps even more impressively, some animals synchronize their migration and breeding periods with the Moon’s phases.

The benefits of moonlight extend beyond living creatures. For example, some plants produce drops of fluid to reflect our satellite’s illumination in a way that attracts beetles and other insects for nighttime pollination.

Where Can I Find Out the Current Lunar Phase?

You can track the Moon’s phases on various reliable websites, but here are the two I use the most:

• Many people use Time and Date AS to keep an eye on various phenomena associated with time zones and solar and lunar activity.
• NASA’s daily Moon guide is an interactive map for observing the Moon each day of the year. It tells you what you’ll see today with the naked eye, a pair of binoculars, and a telescope.

Many wall calendars also display illustrations of the Moon phases. Mine uses a filled-in circle to represent the new moon phase, an empty circle for a full moon, and half-filled circles for the first- and third-quarter phases.

Photographing the Moon can be tricky. When I started trying, all I could shoot was a small, indistinct blob of white. However, once you take the time to learn the technicalities, practice a little patience, and pick up other tips and tricks along the way, you won’t look back!