There are more than 200 moons in the solar system. Some of them orbit the planets while some dwarf planets have moons too. There are also asteroids known to have moons. The small moon called Dactyl was discovered orbiting asteroid Ida in the asteroid belt.
The ringed planet, Saturn, has 82 moons while Mercury and Venus have none. The Earth, on the other hand, has only one natural satellite—the Moon. It is the different phases of Earth’s moon, particularly the waxing gibbous moon phase that we will look at in this post.
The Moon is the brightest object in our night sky. It shines and gives us light at night. However, like everything in the solar system, it does not produce its own light. It reflects light from the Sun.
Since the Moon is not producing this light, many factors can affect its brightness. Its perceived brightness will depend on its position relative to the Earth and Sun.
As we know, everything is moving in space. The Moon orbits the Earth, while the Earth also goes around the Sun. The Sun, in turn, also orbits the center of the Milky Way galaxy. Though, we cannot feel the Sun’s movement because it takes about 225 to 250 million years to orbit the galactic center.
What we can feel instead is the celestial dance between the Moon and Earth in relation to the Sun. Because of this, the Moon appears to change shape throughout a month.
Phases of the Moon
The Moon seems to change shapes throughout the month. These shapes correspond to the eight phases that the Moon goes through in the lunar cycle. This cycle is caused by the Moon’s movement relative to the Sun and Earth.
In understanding the phases of the Moon, we need to remember that the Moon does not really become bigger or smaller. It only “seems” to change from our perspective.
The Moon gets light from the Sun, and like Earth, it also has a dayside and a nightside. As these celestial objects move, the Moon’s dayside is sometimes facing Earth. That’s when we see a Full Moon. When the night side is facing Earth, we get a New Moon.
The Moon undergoes eight phases in the Moon cycle. It has four major phases: New Moon, First Quarter, Full Moon, and Last Quarter. The intermediate phases between them are Waxing Crescent, Waxing Gibbous, Waning Gibbous, and Waning Crescent.
The Moon completes a cycle in 29.5 days, that is, from one New Moon to the next New Moon. This period is called a lunar month.
| Moon Phase | Important Notes |
|---|---|
| 🌑 New Moon | – 0% illumination – First primary phase – Earth-Moon-Sun alignment – The nightside of the Moon faces Earth |
| 🌒 Waxing Crescent | – 0.1% to 49.9% illumination – Intermediate phase – The first sliver of moonlight is seen – The sunlit portion increases |
| 🌓 First Quarter | – 50% illumination – Second primary phase – The Moon, Earth, and Sun form a right angle |
| 🌔 Waxing Gibbous | – 50.1% to 99.9% illumination – Intermediate phase – The sunlit portion continues to increase |
| 🌕 Full Moon | – 100% illumination – Third primary phase – Earth-Moon-Sun alignment – The dayside of the Moon faces Earth |
| 🌖 Waning Gibbous | – 99.9% to 50.1% illumination – Intermediate phase – The sunlit portion decreases |
| 🌗 Last Quarter | – 50% illumination – Fourth primary phase – Also called the – Third Quarter Moon phase – The Moon, Earth, and Sun form a right angle |
| 🌘 Waning Crescent | – 49.9% to 0.1% illumination – Intermediate phase – The sunlit portion continues to decrease – Gives way to the New Moon phase |
What is a Waxing Gibbous Moon?
A Waxing Gibbous Moon is an intermediate phase. It occurs after the First Quarter Moon and before the Full Moon. To put it in context, let’s look at the phases of the Moon.
The lunar cycle starts with a New Moon, also called the dark phase. It is called so because the Moon appears invisible to us in this stage. The reason for this is that the Earth, Moon, and Sun (in that order) form a straight line. The Sun and Moon are on the same side of the Earth.
With the Moon in the middle, one-half of it is illuminated facing the Sun. The other side, which is in darkness, is facing Earth.
Remember
- Waxing: increasing
- Waning: decreasing
- Gibbous: more than half of the Moon is lit
- Crescent: less than half of the Moon is lit
As the Moon continues to orbit Earth in a counter-clockwise direction, it breaks from the straight line. We begin to see the illuminated portion as it enters the Waxing Crescent phase. The sunlit part continues to increase as the Moon continues orbiting the Earth.
When we see a Half Moon or 50% of the sunlit part, the Moon has reached the First Quarter. After that, it will enter the Waxing Gibbous phase.
During a Waxing Gibbous Moon, the illuminated portion appears to be increasing. We can see more than half (50.1% to 99.9%) of it already. From the Half Moon of the First Quarter phase, it is like the transition period that will lead to the Full Moon phase. This time, the Moon grows even brighter.
The Moon will reach its maximum during Full Moon when 100% of its disk is visible. After that, it will enter the waning phases, during which its illumination will decrease. The Waning Gibbous Moon phase will follow, then the Last Quarter Moon. Lastly, the Waning Crescent Moon will be seen before it becomes totally dark—and a new cycle begins.
When Does a Waxing Gibbous Moon Occur?
A Waxing Gibbous Moon is the fourth stage of the lunar cycle. It occurs after the First Quarter Moon and before a Full Moon.
Though it is not a major phase, it takes about 21.6% of the lunar month. Since a lunar month equals 29.5 days, a Waxing Gibbous Moon, on average, occupies about 6 days of the cycle.
Which Side Is Lit Up?
Wherever you are on Earth, observers will see the same percentage of the Moon that is illuminated. The only difference is which side is sunlit.
That means which side of the Moon is lit up depends on the observer’s location. It can appear to be lit up on the right side, left side, and even top or bottom.
As with the other waxing phases, observers in the northern hemisphere will see the Waxing Gibbous Moon lit up on the right side. In the southern hemisphere, it will be the opposite, on the left side. Around the equator, the illuminated part will be the top or bottom portion of the Moon.
We can think of the Waxing Gibbous as the opposite of the Waning Gibbous phase which happens after the Full Moon. As the Moon continues on its journey around Earth, the illuminated portion will shrink from our perspective.
During Waning Gibbous, the sunlit part will be the opposite. It will be the left side as seen in the northern hemisphere and the right side in the southern areas.
The Golden Handle of the Moon
Sunlight can create interesting visual effects as it falls on the Moon’s surface. One of which is the so-called “Golden Handle.”
The dividing line between the bright and dark parts of the Moon is called the “terminator.” During the Waxing Gibbous phases, about two days after the First Quarter, the terminator falls on a mountain range called Montes Jura.
Montes Jura is located on the Moon’s near side (the side of the Moon that is always facing us). It is spread across the northwest portion, covering around 422 kilometers (262 miles). Below this mountain range is the basaltic lava plain called Sinus Iridum (Bay of Rainbows).
The Golden Handle is the stunning visual created when the terminator falls on the Montes Jura range. The high peaks of the mountain are illuminated first while the Bay of rainbows below it is still in darkness.
As the terminator slowly moves, the sunlight dims, creating a golden arc that contrasts with the lava plain below. This results in what is called the Golden Handle. Since it requires the alignment of many factors, we can only catch this unique sight about two nights in every Moon cycle.
Moonrise and Moonset
We might think that the Moon only comes at night. However, we can sometimes see it when the Sun is also up. We call this the “daytime moon” and we can see it best during the First and Third Quarter.
The time when the Moon rises and sets depends on the phase it is in. During a Waxing Gibbous Moon, it rises after noontime. That means, if the Sun’s glare is not too much, we can see it in the daytime before the Sun dips into the horizon.
It will be at its highest point around sunset and is visible for most of the evening. Moonset will be after midnight.
Suitability for Astronomy
Understanding the Moon phases will help us choose the right time to observe the sky.
Stargazing under a Waxing Gibbous Moon will not be very ideal if you want a dark sky. In this phase, it is mostly lit and is approaching Full Moon. It will mostly dominate the night sky and lesser bright objects will not be easily observable.
A Waxing Gibbous Moon will not set after midnight so it is up for most of the night. This is a good opportunity if you want to observe the Moon. After this phase, it will even grow more to become a magnificent Full Moon.
However, if you are after faint stars, galaxies, and other objects, spotting them can be a bit challenging during the Waxing Gibbous phase. The best time for you to do it is during the invisible phase—a New Moon.
The period between the Last and First Quarters is also good for observing other objects. Setting up your telescopes far away from the city lights is also ideal for stargazing.
Effects on the Tides
The tides in our seas and oceans are a result of the gravitational pull of the Moon and the Sun. The tug of these two objects causes the tidal bulge. The Sun is much bigger than the Moon however, its effect on our tides is lesser because of the greater distance.
The biggest differences in our tides happen during New Moon and Full Moon because the Moon, Earth, and Sun are aligned. This way, the pull of gravity from the Moon and Sun is combined. It results in “spring tides” where the high tides are very high and the low tides are very low.
The opposite of spring tides is called “neap tides.” This is when we get the smallest difference in tides.
High tides are not very high and low tides are not very low. This happens during the quarter phases (First Quarter and Last Quarter) when the three objects form a right angle. Because of this position, the gravitational pull of the Moon and Sun is canceled, causing the neap tides.
So what is the tide like during a Waxing Gibbous Moon?
Remember that in this phase, the Moon is transitioning to become a Full Moon. That means the tidal bulge is increasing. It is bigger than the neap tides of the previous phase (First Quarter) but is not yet at its maximum. It will keep on increasing until it reaches the spring tide of the Full Moon.
Interesting Moon Facts
- The Moon takes 27.322 days to complete a revolution around Earth. This is called a sidereal month. However, it takes the Moon longer to complete a cycle, from one New Moon to the next. This is called a synodic month and it is 29.531 days long.
- Sunsets can help in identifying whether the Moon is waxing or waning. If you can see the Moon at sunset, then it is waxing. If you cannot spot it during this time, then it is waning.
- Since the Sun and Moon are not aligned with Earth during Waxing Gibbous, there is no eclipse during this phase. A solar eclipse happens only during a New Moon while a lunar eclipse occurs only during a Full Moon.
- The terminator line of our Moon is sometimes dubbed the “twilight zone.” This is not a fixed structure as it changes with the Moon’s movement. In fact, this line moves at a rate of 9.6 miles per hour (15.4 km per hour).
- The albedo of an astronomical body tells us about its reflectivity. The higher the number, the more light it reflects. Our Moon’s albedo is only about 0.12. That means it reflects only about 12% of the light that it receives from the Sun and absorbs the rest.
- Saturn’s moon, Enceladus, reflects about 100% of the sunlight that hits its surface. It has the highest reflectivity rate (albedo) in the solar system.
Frequently Asked Questions
Does the Moon change its shape?
No, the Moon does not actually change shape. It only seems to change from our point of view here on Earth. The fraction of the sunlit side that we see changes as it orbits the Earth. Because of that, we can sometimes see it in half, in full, or even sometimes, none at all.
What happens during the Waxing Gibbous phase?
During a Waxing Gibbous phase, the Moon’s brightness is increasing. We can already see more than half of it, but not yet 100%. This is an intermediate stage that leads to a Full Moon, the Moon phase after it.
What is the difference between the waxing and waning Moon phase?
Waxing means the sunlit part of the Moon that we see is growing. It happens after the New Moon. The three waxing phases are Waxing Crescent, First Quarter, and Waxing Gibbous.
Waning means the sunlit part of the moon that we see is shrinking. It happens after the Full Moon. The three waning phases are Waning Gibbous, Last Quarter, and Waning Crescent.
How to tell if the Moon is waxing or waning?
Which side of the Moon is lit up tells us if it is waning or waxing. Observers in the northern hemisphere will see the right side of the Moon illuminated during the waxing phases. In the waning phases, the left side is lit up.
If you live in the southern hemisphere, it is the opposite. In places near the equator, it is either the upper or lower part.
| Observers’ Location | Waxing Phases (and other waxing phases) | Waning Phases (and other waning phases) |
|---|---|---|
| Northern Hemisphere | Right half | Left half |
| Southern Hemisphere | Left half | Right Half |
| Equator | Upper half (after moonrise) Lower half (before moonset) | Lower half (after moonrise) Upper half (before moonset) |
Sources:
Image Sources:
The Moon: https://upload.wikimedia.org/wikipedia/commons/thumb/e/e1/FullMoon2010.jpg/330px-FullMoon2010.jpg
Phases of the Moon: https://moon.nasa.gov/internal_resources/359
Waxing Gibbous Moon: https://moon.nasa.gov/internal_resources/365
Waxing gibbous which wide is lit up?:
https://storage.needpix.com/rsynced_images/waxing-gibbous-may-moon-2299301_1280.jpg
Golden Handle: https://earthsky.org/upl/2019/05/Moon-waxing-gibbous-Peter-Lowenstein-Mutare-Zimbabwe-5-15-2019-sq.jpg
Moonrise and moonset (and daylight moon): https://storage.needpix.com/rsynced_images/moon-1538060_1280.jpg
Suitability for Astronomy: https://storage.needpix.com/rsynced_images/house-2589431_1280.jpg
Tides: https://storage.needpix.com/rsynced_images/beach-1168092_1280.jpg