Looking up into the sky each night, we may not see all of the tiny differences that each sunset brings. The tiny shift of the stars and the moon phases are happening constantly whether we’re watching or not. The current lunar phase is easier to recognize by the naked eye.
We’ve all heard of a full moon and the iconic crescent moon is also common, but what about all of the phases in between? What causes this phenomenon and how often do the phases change? Join us as we explore all of these answers and more.
Ironically, the moon’s changing appearance is caused by none other than the sun itself. As the moon orbits the Earth, half of it is constantly illuminated by the sun. In the Northern and Southern Hemispheres we see the various phases depending on the angle of the moon in regards to the Earth.
This delicate rhythm of rotation causes us to various amounts of the illumination on the moon’s surface caused by the sun. A good example is a crescent moon, which is the phase when we only see less than 50% of the moon’s surface illuminated.
The moon orbits the Earth on average every 29.53 days which is just under the normal length of a month (30.44 days). A full lunar cycle is scientifically considered to be the time between two “new moons” which acts as the beginning and end of the cycle. This is known as “lunation” and during the cycle the moon completely circles the Earth.
A full lunar cycle occurs roughly each month, but the timing isn’t exact, which is why many lunar calendars will seem to skip a day. The four principal lunar phases tend to occur every 7.38 days. The moon’s orbit is moderately elliptical though, and this causes the speed of the orbit to vary ever so slightly.
You may have also heard that we always see the same side of the moon throughout each phase. This is true, and a result of a phenomenon called “tidal locking” or “gravitational locking.” This occurs when a celestial body like the moon takes the same amount of time to rotate around its own axis, and its partner.
This creates a situation where the same majority of the orbiting body faces the partner throughout each revolution. The first time we saw the far side of the moon was in 1960’s when a soviet satellite sent back pictures to Earth.
While we tend to generalize that only one side of the moon is seen, another phenomenon known as libration which is a term in astronomy that describes the wobbling or oscillating motion that orbiting bodies tend to have when viewed in a animated motion. In the moon’s case, this is caused by an actual change in the distance between the moon and the Earth as a result of the elliptical orbit it has. Because of this, about 59% of the moon’s surface is visible.
Let’s explore the phases of the moon and how each one appears to the casual observer.
There are a total of eight phases in the lunar cycle. They are also commonly grouped into four principal phases which are the following:
These four phases are combined with four additional intermediate phases to create an entire cycle. Below is an image that shows the full list of phases and the level of the surface visibility for each:
Starting from the beginning of the cycle, it’s easiest to understand each of the phases by examining the principal ones first, then imagining the intermediate ones that fit in between.
This first stage of the cycle occurs when the moon is approximately between the Earth and the sun. The term approximate is used here because the angle of the moon’s orbit is tilted by roughly five degrees in regards to the Earth’s orbit. This is why we don’t see Lunar and Solar eclipses every month.
At this point the side of the moon that is facing Earth does not have any sunlight shining upon it. There is still a visible light however, it is faint but the occurrence of it is known as Earthshine. It happens as a result of sunlight reflecting off of the Earth and onto the darkened surface of the moon.
The best time to see this is when the moon is transitioning from a waning crescent phase into a new moon. A small sliver of the moon will be illuminated by the sunlight and the rest of the sphere will have a soft glow to it. This is Earthshine.
After the new moon phase, the amount of sunlight on the moon’s surface begins to increase. This is known as “waxing” and it encompasses the phase known as “waxing crescent” until the moon is halfway illuminated which is the point of the “first quarter phase.”
As the sunlight continues to fill the surface, we reach the “waxing gibbous” phase which leads directly into our next principal step.
Similar to the new moon phase, a full moon places the all three celestial bodies into alignment. The difference here is that the moon is on the opposite side of the Earth. On a diagram from right to left we have sun, Earth, moon. This allows the entire visible side of the moon to be illuminated which is how we see a “full moon” as it were.
After the full moon has become visible, the process begins again, but in reverse. These final stages are known as “waning” phases. Similar to before the light will begin to retreat causing a waning gibbous phase followed the last quarter where the light is once again only illuminating 50% of the surface.
Following this quarter the light continues to decrease until we reach the waning crescent phase. It’s important to note that here is when the aforementioned reflection of the sun’s light off the Earth known as Earthshine can be seen. This continues until all of the light is gone and we reach another new moon.
When it comes to astrological signs like the signs of the Zodiac, most people are aware of the Sun signs, but not the moon ones. While the sun signs are most important for horoscopes and predictions, the moon comes in at a close second. Astrological beliefs hold that these signs affect our senses and the unconscious side of our personalities.
The moon versions of these popular signs are divided into four categories: air, fire, earth, and water. Your sign is calculated by the month, time, and location you were born in and predicts elements of your personality based on the sign applied to you. Below is an examination of each category and how those individual signs predict the unconscious side of our personalities:
Unlike the sun versions of these signs, the moon counterparts are more focused on how a person tends to feel or think subconsciously. An example is Gemini which tends tell others about new information they’ve learned. They are prone to being people who will speak as much as needed to have their feelings known.
People born under the Libra sign desire to be loved and accepted above all else, and finally the Aquarius sign causes people to think before they act and always talk to others in the hopes of reaching an understanding in various situations.
People who are born under one of these signs tend to be very sure of their actions and decisions. When they come to a conclusion or a decision, they are extremely passionate in voicing it to others and making it known. Sagittarius in particular tends to result in people who are nomadic and like to move around constantly.
People born under these signs tend to be very in tune with their emotions. Taurus for example tends relate to people who try to avoid to conflict because they prefer calm scenarios. Those born under the Virgo sign like to be in the know and constantly aware of what’s happening. They prefer organization.
Capricorn signs encompass people who try and control their emotions. They don’t speak out and keep most of their thoughts and opinions to themselves.
On the opposite side of the spectrum are the water signs who value expression above all else. They want others to take care of the, but they are also willing to take care of those they trust and love. Being able to freely express their emotions is a priority for those born under this sign.
These two types of events refer to the alignment of three celestial objects:
In addition to this, there are three types of eclipses: total, partial, and annular. A lunar eclipse occurs when the Earth moves between the moon and the sun. At this point, the Earth’s shadow blocks the entire moon, or a portion of it. A solar eclipse is the same concept, but the moon is now blocking the sun either partially or fully.
The final type of eclipse, the annular one, happens when the moon is at its furthest point in orbit. It does not cover the sun completely, which leaves a thin ring of light around the edge of the moon in the sky.
There are various things that need to occur for an eclipse to happen, which is why they are exceedingly rare, especially solar eclipses.
The moon is a constant magnificent part of the night sky. Now that you have a greater understanding of the moon phases, you can continue to explore the science behind them and the astrological beliefs that have been built around them. In the meantime, enjoy these interesting facts about our moon:
Thanks as always for reading and be sure to tell me about your thoughts on the moon phases, the zodiac, and anything else you want to chime in on!