Phases of the Moon

A complete scientific and historical guide the phases of the moon including facts and links for kids.

The Moon phases are commonly known as lunar phases, and they represent the different shapes the Moon takes when it is illuminated by the Sun as viewed from Earth.

These lunar phases change regularly throughout the synodic month  – every 29.53 days, as the positions of the Earth and Moon around the Sun shift.

The Moon is tidally locked to our Earth’s gravity, and this prevents its rotation, causing only one facet of the Moon to always face us. This side of the Moon is variously sunlit, which is dictated by the Moon’s position in its orbit.

Therefore, the sunlit portion of this face, also known as the near side, can vary from 0% – at new Moon – to 100% at full Moon. The twilight zone, or the moving line that divides the daylit side and the night side of the Moon, known as the lunar terminator, is the boundary between the sunlit portion of the Moon and its darkened hemispheres.

Moon Phase for Saturday Dec 5th, 2020

Phase name: Waning Gibbous

Moon age: 19.81 days

Moon illumination: 80.74%

Moon tilt: -43.107°

Moon sign: Leo


Phases of the Moon

There are four principle lunar phases in the western culture, known as the New Moon, First Quarter, Full Moon, and Third Quarter. These phases last for around 7.4 days; however, they vary slightly due to the Moon’s elliptical-shaped orbit.

There are also four intermediate phases, Waxing Crescent, Waxing Gibbous, Waning Gibbous and Waning Crescent.

Apart from a couple of craters near the lunar poles, such as the famous Shoemaker crater, all parts of the Moon are susceptible to around 13.77 days of light, followed by 13.77 days of night.

The darkest part of the Moon is the one always facing away from us, and it is commonly referred to as the dark side of the Moon. The Moon’s four principal phases occur when the Moon’s ecliptic longitude is at an angle to the Sun, as viewed from our planet, at 0°, 90°, 180°, and 270°, respectively.

All of these phases appear at slightly different times at different locations on Earth. There are also intervals between these principal phases, where the Moon’s apparent shape is either crescent or gibbous.

The intermediate phases of the Moon last one-quarter of a synodic month, or 7.38 days on average. The term waxing is used for an intermediate stage when the Moon’s apparent shape is thickening, from new to full Moon, and the term waning is applied when it is thinning.

The most extended duration between the full Moon to new Moon, or vice versa, lasts for around 15 days and 14.5 hours, while the shortest period lasts only about 13 days and 22.5 hours.

Principal and Intermediate Phases of the Moon
Moon Phase Northern Hemisphere Southern Hemisphere Visibility Average moonrise time Mid-phase standard time Average moonset time
New Moon Disc entirely in Sun's shadow - lit by earthshine only Invisible - too close to the Sun 6 am - 06.00 Noon 6 pm - 18:00
Waxing Crescent Right side, 0.1% - 49.9% lit disc Left side, 0.1 - 49.9% lit disc Late morning to post-dusk 9 am - 09:00 3 pm - 15:00 9 pm - 21:00
First Quarter Right side, 50% lit disc Left side, 50% lit disc Afternoon and early evening Noon 6 pm - 18:00 Midnight - 00:00
Waxing Gibbous Right side, 50.1% - 99.9% lit disc Left side, 50.1% -99.9% lit disc Late afternoon and during the night 3 pm - 15:00 9 pm - 21:00 3 am - 03:00
Full Moon 100% Illuminated disc Sunset to sunrise - all night 6 pm - 18:00 Midnight - 00:00 6 am - 06:00
Waning Gibbous Left side, 99.9% - 50.1% lit disc Right side, 99.9% - 50.1% lit disc Most of the night and early morning 9 pm - 21:00 3 am - 03:00 9 am - 09:00
Last Quarter Left side, 50% lit disc Right side, 50% lit disc Late night and morning Midnight - 00:00 6 am - 06:00 Noon
Waning Crescent Left side, 49.9% - 0.1% lit disc Right side, 49.9% - 0.1% lit disc Pre-dawn to early afternoon 3 am - 03:00 9 am - 09:00 3 pm - 15:00

The New Moon appears higher on the summer solstice than on the winter solstice, while the First Quarter Moon appears higher on the spring equinox than on the autumnal/fall equinox.

The Full Moon appears higher on the winter solstice than on the summer solstice, while the Last Quarter Moon appears higher on the autumnal/fall equinox than on the spring equinox.

The Waxing Crescent Moon appears higher on the mid-spring – May 5 in the Northern Hemisphere / November 7 – Southern Hemisphere, than on the mid-autumn – November 7 in the Northern Hemisphere / May 5 in the Southern Hemisphere.

The Waxing Gibbous Moon appears higher on mid-winter – February 4 in the Northern Hemisphere / August 7 in the Southern Hemisphere, than on the mid-summer – August 7 in the Northern Hemisphere / February 4 in the Southern Hemisphere.

The Waning Gibbous Moon appears higher on the mid-autumn – November 7 in the Northern Hemisphere / May 5 in the Southern Hemisphere – than on mid-spring – May 5 in the Northern Hemisphere / November 7 in the Southern Hemisphere.

The Waning Crescent Moon appears higher on the mid-summer – August 7 in the Northern Hemisphere / February 4 in the Southern Hemisphere – than on mid-winter – February 4 in the Northern Hemisphere / August 7 in the Southern Hemisphere.

Waxing and Waning

If the Sun and the Moon are aligned on Earth’s same side, then the Moon is termed as “new,” and the side of the Moon facing Earth is not illuminated by the Sun.

When the Moon “waxes” – the amount of illuminated surface as seen from Earth is increasing, and the lunar phases progress through new Moon, crescent moon, first-quarter Moon, gibbous Moon, and Full Moon.

The Moon is then said to “wane” as it passes through the gibbous Moon phase, third-quarter Moon, crescent Moon, and then back to New Moon.

The expressions old Moon and new Moon are not interchangeable. The old Moon is a waning silver that becomes invisible to the naked eye, until the moment when it aligns with the Sun and begins to wax, at which point it becomes new again.

The term “half Moon” is commonly used to mean the first- and third-quarter Moon phases, while the term quarter itself refers to the extent of the Moon’s cycle around the Earth, and not its shape.

When an illuminated hemisphere is viewed from a certain angle, the portion of the illuminated area, which is visible, will appear as a two-dimensional shape as defined by the intersection of an ellipse and circle.

The ellipse’s central axis coincides with the circle’s diameter. If the half-ellipse is convex to the half-circle, then the shape will be gibbous – bulging outwards – and if the half-ellipse is concave for the half-circle, then the profile will be a crescent. When a crescent Moon occurs, the earthshine phenomenon may be visible, where the darker side of the Moon dimly reflects indirect sunlight reflected from Earth.

Earthshine Effect

If the Moon, as seen from Earth, is a thin crescent, then Earth, as viewed from the Moon, is almost entirely lit by the Sun. Commonly, the dark side of the Moon is dimly lit by indirect sunlight reflected from Earth; however, it is bright enough to be seen from Earth.

This phenomenon is known as earthshine, and sometimes it is described as “the old moon in the new moon’s arms” or “the new moon in the old moon’s arms.”

Latitude Orientation

In the Northern Hemisphere, if the left/east side of the Moon is dark, then the brightest part is thickening, and the Moon is described as waxing – shifting towards the Full Moon phase.

If the right/west side of the Moon is dark, then the bright part is thinning, and the Moon is described as waning – it is past full and shifting towards the New Moon phase.

If the observer is situated in the Northern Hemisphere, the Moon’s right side is the part that is always waxing – that is, if the right side is dark, the Moon is darkening; if the right side is lit, the Moon is brightening.

In the Southern Hemisphere, the Moon is viewed through an inverted perspective, or rotated at 180°, to that of the Northern Hemisphere, and to all of the images posted here. As such, the opposite sides appear to either wax or wane.

Close to the equator, the lunar terminator – or twilight zone – will appear horizontal during the mornings and evenings. Since the descriptions above of the lunar phases only apply at high and middle latitudes, observers moving towards the tropics from either northern or southern latitudes will view the Moon rotated anti-clockwise or clockwise. (About the pictures from this post)

The lunar crescent can open upward or downward, with the “horns” of the crescent pointing up or down, respectively. When the Sun appears above the Moon in the sky, the crescent opens downward, while when the Moon is above the Sun, the crescent opens upward.

The most precise and brightest crescent Moon may be visible when the Sun is below the horizon, which implies that the Moon must be above the Sun from our perspective, and the crescent is thus opened upward.

This is the orientation in which the crescent Moon is most often seen from the tropics. The waxing and waning crescents look quite similar; however, the waxing crescent appears in the western sky in the evening, while the waning crescent in the eastern sky appears in the morning.

Moon Phases Calendar

The cycle of lunar phases / synodic month repeats every 29.53 days, while the Gregorian calendar month lasts for around 30.44 days. For each successive month, the timing of the lunar phase shifts by an average of almost one day. One lunar year is equivalent to 354 days.

If you want to create a Moon Phase calendar, one must photograph the Moon’s phase every day for a month. This procedure should start in the evening after sunset and will be repeated every 24 hours and 50 minutes later, ending in the morning before sunrise.

On a calendar listing moonrise or moonset times, some days may appear to be skipped. This is because the Moon follows a predictable orbit every month.

The skipped day is a feature of the Moon’s eastward movement in relation to the Sun, which at most latitudes will cause the Moon to rise later each day.

Calculating Phase

The four intermediate lunar phases, the New Moon, First Quarter, Full Moon, and Third Quarter, last for almost a week / 7.38 days on average; however, they vary slightly due to the lunar apogee and perigee.

The days counted from a New Moon is the Moon’s age, with each cycle of phases known as a lunation. The approximate age of the Moon may be calculated for any date by summing the days since a New Moon, like for example, January 1, 1900, or August 11, 1999, and then reducing this modulo 29.530588853 – the length of a synodic month.

The difference between two dates can be summed by subtracting the Julian day number of one from that of the other, or simpler formulae are giving the number of days since December 31, 1899.

However, this method of calculus assumes a perfectly circular orbit. It makes no allowance for the time of day at which the New Moon occurred and, therefore, may be incorrect by several hours.

The accuracy is even further reduced if the difference between the required date and the reference date is more considerable.

Effect of Parallax

The Earth spans an angle of about two degrees when seen from the Moon. Thus, an observer from Earth views the Moon when it is close to the eastern horizon from an angle that is around 2 degrees different from an observer who sees the Moon from the western horizon.

The Moon moves for around 12 degrees throughout its orbit per day; thus, if we, the observers, were stationary, we would see the phases of the Moon at times that differ by around one-sixth of a day / 4 hours.

However, we are on the surface of a continually rotating Earth. Thus, if a person sees the Moon on the eastern horizon, another would see it on the western horizon around twelve hours later. This adds a fluctuating factor to the apparent progression of the lunar phases.

These events occur slower when the Moon is high in the sky than when it is below the horizon. The Moon appears to move unevenly, and this can be applied towards its phases as well.

The four hour oscillation period is a small fraction of a month, and it doesn’t have a significant effect on the Moon’s appearance; however, it does affect the lunar phases calculation methodology and its accuracy.

Related Questions

What is Synodic Month?

The lunar month is also known as the synodic month, and it refers to a measured period of time. In this case, the synodic month is measured from a Moon phase until the return of that exact phase. The average duration for this measurement is usually at around 29.5 days.

What are the Moon  Phases?

The Moon goes through different appearance phases since it orbits our Earth, causing a portion of its surface to be illuminated, which later changes in shape. This is why the Moon has phases.

The Moon orbits our Earth roughly every 27.3 days; however, the synodic month, or lunar month, lasts for 29.5 days. This happens because the Moon is catching us up from behind in around 2.2 days. After all, Earth is moving faster.

What is the Harvest Moon?

The Harvest Moon is when a full moon occurs close to the autumnal equinox (when night and day are equal). The Moon is referred to as the Harvest Moon in this event due to its bright appearance in the sky, which allowed farmers to work longer into the fall night, reaping spring’s rewards and summer labors.

Because the equinox falls in late September, the full Moon in September is often given this name. However, it can happen in October as well. Every full Moon has its own name, and they are associated with either ancient deities, agriculture, weather, or other things. Here are their names:

  • January – Moon after Yule or Wolf Moon
  • February – Snow Moon
  • March – Sap Moon
  • April – Grass Moon
  • May – Planting Moon
  • June – Honey Moon
  • July – Thunder Moon
  • August – Grain Moon
  • September – Fruit or Harvest Moon
  • October – Hunter of Harvest Moon
  • November – Frosty Moon
  • December – Moon before Yule

What is a Blue Moon?

A whole month isn’t equal to two Full Moon’s. However, around three years, there are two full Moon’s in one calendar month. In recent times, the secondary full Moon has often been termed as the Blue Moon.

Blue Moons are rare since they occur once every 33 months. No one knows who coined the name, Blue Moon, but it is entirely plausible that it received this name since the Moon does appear bluish.

High altitude particles may cause this; however, some believe that the name comes from an old phrase: “once in a blue moon.”

Why do we see Only One Face of the Moon?

Due to the Earth and Moon’s gravitational interactions, Earth’s natural satellite has begun to slow down in rotational velocities. Because of this, the Moon completes one rotation on its axis at exactly the same time when it completes an orbit around our Earth.

This gravitational drain has a mutual effect, though. Our Earth’s rotational speed is also slowed down by these interactions, with its products being easily observed in ocean tides.

When Does the Young Moon Become Visible in the Evening Sky?

Three principal factors determine the young Moon’s visibility in the evening sky:

  • The sky’s clarity
  • The angle of the ecliptic in regards to the horizon
  • The accuracy of the observer’s eyesight

If the ecliptic is perpendicular to the horizon, then the young Moon appears visible to the naked eye much earlier.

What is a Wolf Moon?

In ancient times, people referred to the Full Moon that occurred in January, as the Wolf Moon. Many believe that this was because the wolves howled much more fiercely in this month, perhaps due to a lack of food. The January full Moon is also known as the Moon before Yule.

What is the Moon Schedule for 2020?

The Moon schedule for 2020 is quite ordinary since, in 2020, we will see twelve New Moon’s, thirteen First Quarter’s, and Full Moon’s, and twelve Last Quarter Moon phases, according to NASA. Interesting to note is that the first Full Moon in January this year is a Wolf Moon, and it arrives with a lunar eclipse, while the Full Moon on March 9 is a Worm Supermoon.

Moon Schedule 2020
 

New Moon

 

First Quarter

 

Full Moon

 

Last Quarter

 

 

January 2 – 11:45 pm / 23:45

 

January 10 – 2:21 pm / 14:21

Wolf Moon Lunar Eclipse

 

January 17 – 7:58 am / 07:58

 

January 24 – 4:42 pm / 16:42

 

February 1 – 8:42 pm / 20:42

 

February 9 – 2:33 am / 02:33

 

February 15 – 5:17 pm / 17:17

 

February 23 – 10:32 am / 10:32

 

March 2 – 2:57 pm / 14:57

 

March 9 – 1:48 pm / 13:48

Super Worm Moon

 

March 16 – 5:34 am / 05:34

 

March 24 – 5:28 am / 05:28

 

April 1 – 6:21 am / 06:21

 

April 7 – 10:35 pm / 22:35

Super Pink Moon

 

April 14 – 6:56 pm / 18:56

 

April 22 – 10:26 pm / 22:26

 

April 30 – 4:38 pm / 16:38

 

May 7 – 6:45 am / 06:45

Flower Supermoon

 

May 14 – 10:03 am / 10:03

 

May 22 – 1:39 pm / 13:39

 

May 29 – 11:30 pm / 23:30

 

June 5 – 3:12 pm / 15:12

 

June 13 – 2:24 am / 02:24

 

June 21 – 2:41 am / 02:41

 

June 28 – 4:16 pm / 16:16

 

July 5 – 12:44 am / 12:44

 

July 12 – 7:29 pm / 19:29

 

July 20 – 1:33 pm / 13:33

 

July 27 – 8:32 am / 08:32

 

August 3 – 11:59 am / 11:59

 

August 11 – 12:45 pm / 12:45

 

August 18 – 10:41 pm /

22:41

 

August 25 – 1:58 pm / 13:58

 

September 2 – 1:22 am / 01:22

 

September 10 – 5:26 am / 05:26

 

September 17 – 7:00 am / 07:00

 

September 23 – 9:55 pm / 21:55

 

October 1 – 5:05 pm / 17:05

 

October 9 – 8:39 pm / 20:39

 

October 16 – 3:31 pm / 15:31

 

October 23 – 9:23 am / 09:23

 

October 31 – 9:49 am / 09:49

 

November 8 – 8:46 am / 08:46

 

November 15 – 12:07 am / 12:07

 

November 21 – 11:45 pm / 23:45

 

November 30 – 4:30 am / 04:30

 

December 7 – 7:37 pm / 19:37

 

December 14 – 11:17 am / 11:17

 

December 21 – 6:41 pm / 18:41

 

December 29 – 10:28 pm / 22:28

 

What is a Worm Moon?

The Worm Moon is a Full Moon, which traditionally bears this name because earthworms and grubs will emerge from their winter dormancy during this period, marking the arrival of spring. In 2020, the first Super Worm Moon occurred on March 9.

Other powerful supermoons that occurred in 2020 were the April Super Pink Moon, – which was the first Full Moon of spring this year, and the Flower Supermoon, which was the last supermoon of 2020, and it occurred on May 7.

Did you Know?

– The Moon orbits the Earth with an average speed of around 2.300 mi / 3.700 km per hour.

– There is an average distance between the Earth and the Moon, which is estimated at approximately 238,900 mi / 384,000 km.

– Our Moon is the fifth-largest natural satellite in the Solar System; however, it is considerably smaller than Jupiter and Saturn’s biggest moons.

– The first uncrewed spacecraft to land on the Moon was the Luna 1 Spacecraft, conducted by the soviets in 1959. The first crewed spacecraft to land on the Moon was Apollo 11, led by the USA, in 1969.

– Quakes occur on the Moon, the same as on Earth, but they are known as moonquakes.

– During a Full Moon, a person’s overall weight is somewhat affected due to stronger gravitational interactions. This is when the most potent tidal activities also occur.

– Many scientists believe that the Moon is a chunk of Earth, which was blown into space after a massive collision. Some estimate that the Moon is 4.5 billion years old.

– Scientists have observed the so-called rusting of the Moon. This event exists solely because the Moon passes through Earth’s magnetic field, which temporarily protects it from solar radiation, and individual particles from Earth’s atmosphere reach the Moon unhindered.

Sources:

[1.] Wikipedia

[2.] NASA

[3.] Timeanddate

[4.] Moongiant

[5.] Stardate

[6.] Moonphases

Image Sources:

[1.] https://solarsystem.nasa.gov/system/downloadable_items/940_moon_phases.png

[2.] https://spaceplace.nasa.gov/review/dr-marc-earth/Moon_phases_drawing.gif

[3.] https://upload.wikimedia.org/wikipedia/commons/thumb/4/46/Moon_phases_en.jpg/1024px-Moon_phases_en.jpg

[4.] https://upload.wikimedia.org/wikipedia/commons/6/6a/Moon_Phase_Diagram_for_Simple_English_Wikipedia.GIF

[5.] https://images.immediate.co.uk/production/volatile/sites/25/2020/02/Moon-earthshine-eb6a15e.jpg?quality=45&resize=768,574

[6.] https://www.wesharethesamemoon.org/resources/activities/extras/PhasesChart.png

[7.] https://www.jpl.nasa.gov/edu/images/activities/superbloodmoon.png

[8.] https://cdn.vox-cdn.com/thumbor/zHQY6_Rqx7XG_NsDtjrTzFxE3bA=/0x0:7087×4252/1200×800/filters:focal(2978×1560:4110×2692)/cdn.vox-cdn.com/uploads/chorus_image/image/67196083/1419326061.0.jpeg

[9.] https://hips.hearstapps.com/hmg-prod.s3.amazonaws.com/images/full-frame-of-the-supermoon-of-yellow-color-on-a-royalty-free-image-913323028-1552062023.jpg?crop=0.752xw:1.00xh;0.121xw,0&resize=980:*

[10.] https://upload.wikimedia.org/wikipedia/commons/9/9d/Moon_phase_calendar_May2005.jpg