How Much of the Moon is Always Lit?

The Moon seems to undergo a strange transformation each month as it seemingly grows and shrinks in the sky. There’s obviously much more to the story. To discover what’s happening on the Moon, we need to understand where this light comes from and where it goes. Read on to get to the bottom of the mystery surrounding how much of the Moon is always lit.

How Much Of The Moon Is Always Lit

A Near Side and a Far Side of the Moon

The Moon and the Earth have a rather unique dynamic in the sky. Should you gaze up at the sky on any given day, you’ll notice that the surface of the Moon never changes. Sure, you may see more or less of the Moon depending on the time of the month, but the Moon’s face is always the same.

The Moon is a spherical object, just like our Earth. While the Earth spins separately from its revolution, taking 24 hours to spin and just over 365 days to travel around the Sun.

In the past, the Moon did rotate just like the Earth, but the Earth’s gravity is holding onto the Moon so tightly that it no longer rotates in a traditional way. Today, the Moon rotates and revolves at the exact same time. This phenomenon is called tidal locking.

Tidal Locking
As the moon takes exactly one orbit to rotate one about its axis, we will never be able to see the green side of the moon. (Image credit: Smurrayinchester on Wikimedia Commons CC BY-SA 3.0)

Because of this, there’s a side of the Moon that we never see from Earth. 

Phases of the Moon

Moon Phases
Phases of the Moon.

As the Moon travels around our Earth, it certainly gives the perception that it is more lit at certain times and less lit during others. The Moon gives off no light of its own, and the light we see from the Moon is actually a reflection of the Sun’s rays off the lunar surface. 

For instance, during a full Moon, we are able to see the entire surface of the Moon as it shines down on us. Roughly two weeks later, we look up at the same sky and there’s no Moon to see at all.

In between those two phases, the Moon appears to either be getting larger or getting smaller with each passing day. 

You’ve probably deciphered that the Moon isn’t actually disappearing. When the Sun’s light stops shining on a part of the Moon, the lack of light is so absolute that this part of the Moon seems invisible to us.

Can it truly be that the Sun stops shining on the Moon at certain times of the month?

How Much of the Moon Is Always Lit (Even if We Can’t See It)?

How Much Of The Moon Is Always Lit
The same amount of sunlight reaches the Moon no matter what phase we currently see in our sky.

There’s a common misconception that the far side of the Moon is dark, cold, and never receives any sunlight. This, however, is not the case.

No matter what phase of the Moon we currently see in our sky, the same amount of sunlight reaches the Moon at any given time. Even if the Moon looks to us like a sliver in the sky, that simply means the far side of the Moon is almost completely bathed in sunlight. 

Of course, the opposite holds true as well. If most of the Earth-facing side of the Moon is lit up for us to see, most of the far side of the Moon is currently dark. In fact, the only time the far side of the Moon sees no sunlight is when we are experiencing a full Moon.

Our new Moon indicates that the far side of the Moon is completely lit. Unfortunately, no one in the known universe is able to see it!

With one exception that we’ll look at in just a moment, the Moon is always exactly 50% lit by the Sun’s rays.

How Many Full Moons Are There per Year?

How Many Full Moons Are There Per Year
A Full moon behind a tree silhouettes.

The Moon passes through its phases once roughly every 29.5 days. Knowing what we now know about how the Sun casts its glow on the Moon, we can better understand how often all of the Sun’s rays shine on the side of the Moon that we can see.

A full moon occurs just once during those 29.5 days. This happens when the Moon is furthest away from the Sun in its orbit around the Earth. We’re all used to seeing a full Moon once a month, and most years do have exactly 12 full Moons.

Since a lunar month is slightly less than a month on Earth, we see a total of 13 full Moons every few years. One month ends up having two full Moons, a phenomenon we call a Blue Moon.

Interestingly enough, February, with its 28 (or 29) days, has no full Moon once every 19 years. When this happens, both January and March have Blue Moons that year!

The Lunar Eclipse

Total Lunar Eclipse
A nearly total lunar eclipse is seen as the full moon is shadowed by the Earth on the arrival of the winter solstice, Tuesday, December 21, 2010. (Image credit: NASA)

There actually is one instance where the Moon does not receive any light from the Sun, but it only happens for a short while. As the Moon travels around the Earth, it does once a month move behind our planet in relation to the Sun.

It is almost always just above or just below the Earth in the cosmic plane, and sunlight reaches the lunar surface uninhibited. This event is nothing more than our monthly full Moon.

However, once in a great while, the Moon will find itself directly behind the Earth. In this situation, the Moon passes through Earth’s shadow, and the Earth temporarily blocks the Sun’s light from shining on the Moon.

We know this occurrence as a lunar eclipse. As the full Moon passes into Earth’s shadow, it slowly disappears from the night sky until it vanishes completely. As quickly as it disappeared, the Moon slowly reappears in the night sky until the Moon moves out from the Earth’s shadow.

An entire lunar eclipse can take a few hours, with the Moon being totally invisible for around 15 minutes.


This celestial optical illusion that the Sun and Moon play on us has intrigued people for millennia. Some cultures thought the Moon was being eaten each month, and others were able to use the phases of the Moon to track when to plant and harvest crops.

While the Sun’s light is something easily taken for granted, it’s necessary for life on our planet and allows us to appreciate how beautiful our Moon truly is.

About Noah Zelvis

Noah is a content writer who has had a love of all things astronomy for as long as he can remember.
When not reaching for the stars, you’ll likely find Noah traveling or running.