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The deliberate misidentification of a Waxing Gibbous Moon ("waxing" means going from new to full; that is increasing in illuminated area) as a "wax gibbon" (a Southeast Asian ape made of a nonpolar solid) is a source of humor in this comic. This is probably a reference to H.P. Lovecraft, who had several of his stories take place under "a gibbous moon" for dramatic effect, or even more likely a reference to the {{w|Discworld}} by {{w|Terry Pratchett}}, often referenced in xkcd (as in [[1498: Terry Pratchett]]). In the witch series the Gibbous Moon is mentioned several times as the most magic, rather than the more often used Crescent or Full Moon.
 
The deliberate misidentification of a Waxing Gibbous Moon ("waxing" means going from new to full; that is increasing in illuminated area) as a "wax gibbon" (a Southeast Asian ape made of a nonpolar solid) is a source of humor in this comic. This is probably a reference to H.P. Lovecraft, who had several of his stories take place under "a gibbous moon" for dramatic effect, or even more likely a reference to the {{w|Discworld}} by {{w|Terry Pratchett}}, often referenced in xkcd (as in [[1498: Terry Pratchett]]). In the witch series the Gibbous Moon is mentioned several times as the most magic, rather than the more often used Crescent or Full Moon.
  
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Further, because the light portion of the Moon is illuminated by sunlight (whether or not the Moon is in the sky at the same time as the Sun), the light side of the Moon will always be facing towards the Sun. If the Moon is in the night sky, the Sun must be somewhere "below" the horizon on the other side of the Earth. Thus, at night, the light portion of the Moon must always be on the half of the Moon that faces the horizon (there are points during the daytime when the orientation can go the other way); however, because of the [https://www.seas.upenn.edu/~amyers/MoonPaper20June.pdf moon tilt illusion] it is possible for the light portion of the moon to appear to point up. The [https://www.academia.edu/7848972/THE_MOON_TILT_ILLUSION moon tilt illusion] is generally not as severe and may only last a few hours after sunset.
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Further, because the light portion of the Moon is illuminated by sunlight (whether or not the Moon is in the sky at the same time as the Sun), the light side of the Moon will always be facing towards the Sun. If the Moon is in the night sky, the Sun must be somewhere "below" the horizon on the other side of the Earth. Thus, at night, the light portion of the Moon must always be on the half of the Moon that faces the horizon (there are points during the daytime when the orientation can go the other way); however, because of the [http://www.seas.upenn.edu/~amyers/MoonPaper20June.pdf moon tilt illusion] it is possible for the light portion of the moon to appear to point up. The [https://www.academia.edu/7848972/THE_MOON_TILT_ILLUSION moon tilt illusion] is generally not as severe and may only last a few hours after sunset.
  
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It is worth noting that while the Moon's dark portion blends imperceptibly with the dark night sky, it is still a solid body. Therefore, it would be impossible to see more distant objects such as stars "through" the dark portion of the Moon's circumference. This is most dramatically exemplified by a {{w|solar eclipse}} during which the Moon passes in front of the Sun and is therefore completely dark (the Sun is lighting only the far side), but the Moon's circumference still blocks a circular portion of the Sun's light.  Therefore, if we were to see any lights in the part of the sky the dark side of the Moon blocks, they would need to be from sources between us and the Moon's surface, such as a nuclear war on the moon.
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It is worth noting that while the Moon's dark portion blends imperceptibly with the dark night sky, it is still a solid body. Therefore it would be impossible to see more distant objects such as stars "through" the dark portion of the Moon's circumference. This is most dramatically exemplified by a {{w|solar eclipse}} during which the Moon passes in front of the Sun and is therefore completely dark (the Sun is lighting only the far side), but the Moon's circumference still blocks a circular portion of the Sun's light.  Therefore, if we were to see any lights in the part of the sky the dark side of the Moon blocks, they would need to be from sources between us and the Moon's surface, such as a nuclear war on the moon.
  
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This comic lists some of some common mistakes. In some cases, a depiction may be unrealistic in multiple ways - for example, the {{w|Flag of Tunisia}} has both unrealistic horns and a star visible between the horns, while {{w|File:Moon tarot charles6.jpg|the Charles VI tarot}} shows a Moon with over-long horns pointing towards the horizon.
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This comic lists some of the some common mistakes. In some cases, a depiction may be unrealistic in multiple ways - for example, the {{w|Flag of Tunisia}} has both unrealistic horns and a star visible between the horns, while {{w|File:Moon tarot charles6.jpg|the Charles VI tarot}} shows a Moon with over-long horns pointing towards the horizon.
  
 
In the title text, Randall is referring to the movie {{w|Independence Day (1996 film)|''Independence Day''}} and how one of the alien's ships (in the movie) 'eclipses' part of the Moon. He says that if the points go halfway or longer around the Moon, then he imagines it's caused by an alien ship and interprets the entire piece of art in that context (i.e. aliens are about to attack those shepherds!).
 
In the title text, Randall is referring to the movie {{w|Independence Day (1996 film)|''Independence Day''}} and how one of the alien's ships (in the movie) 'eclipses' part of the Moon. He says that if the points go halfway or longer around the Moon, then he imagines it's caused by an alien ship and interprets the entire piece of art in that context (i.e. aliens are about to attack those shepherds!).
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|3 ||[[File:moon4a.jpg]]|| Crescent moon with horns away from horizon || <font color="green">Normal</font> || Reality, as in this is how one of the moon's phases looks on a normal basis. || LOOK AT THE MOON
 
|3 ||[[File:moon4a.jpg]]|| Crescent moon with horns away from horizon || <font color="green">Normal</font> || Reality, as in this is how one of the moon's phases looks on a normal basis. || LOOK AT THE MOON
 
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|4 ||[[File:moon3.jpg]]|| Crescent moon with horns towards horizon ||  <font color="red">Not&nbsp;normal</font> || Not possible at night || This can only happen when the sun is above the horizon. Since a crescent moon means that the Sun and the Moon are relatively close in the sky, the Moon would not be visible with a naked eye, its light completely outshone by the sunlight. Randall comments that this is possible only during the daytime, marking it wrong as the background would not be black. According to this [https://en.wikipedia.org/wiki/Lunar_phase#/media/File:Moon_phases_en.jpg image] on Wikipedia's article on {{w|lunar phase}} "Phases of the Moon, as seen looking southward from the {{w|northern hemisphere}}. The {{w|southern hemisphere}} will see each phase rotated through 180°". This might seem to indicate that shape #3, which is visible in for instance USA where Randall lives should be seen like #4 in the southern part of South America, also at night! However, because the light portion of the moon is illuminated by sunlight (whether or not the moon is in the sky at the same time as the sun), the light side of the moon will always be facing towards the sun. If the moon is in the night sky, the sun must be somewhere "below" the horizon on the other side of the Earth. Thus, at night, the light portion of the moon must always be on the half of the moon that faces the horizon; However, in the case of twilight after sunset and shortly after (like the example painting), due to the [https://www.academia.edu/7848972/THE_MOON_TILT_ILLUSION moon tilt][https://www.seas.upenn.edu/~amyers/MoonPaper20June.pdf illusion] the bright side of the moon may appear to point up relative to an observer on the ground (although not to the extent show in the comic). But as the text from Randall points out there can be times during daytime when the orientation can go the other way. But then the background should not be black. Originally Randall wrote a different (wrong) sentence here and then corrected to the one currently explained, see [[#Trivia|trivia]] below.|| Van Gogh, {{w|File:Van Gogh - Passeio ao Crepúsculo.jpg|Landscape with Couple Walking and Crescent Moon}}
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|4 ||[[File:moon3.jpg]]|| Crescent moon with horns towards horizon ||  <font color="red">Not&nbsp;normal</font> || Not possible at night || This can only happen when the sun is above the horizon. Since a crescent moon means that the Sun and the Moon are relatively close in the sky, the Moon would not be visible with a naked eye, its light completely outshone by the sunlight. Randall comments that this is possible only during the daytime, marking it wrong as the background would not be black. According to this [https://en.wikipedia.org/wiki/Lunar_phase#/media/File:Moon_phases_en.jpg image] on Wikipedia's article on {{w|lunar phase}} "Phases of the Moon, as seen looking southward from the {{w|northern hemisphere}}. The {{w|southern hemisphere}} will see each phase rotated through 180°". This might seem to indicate that shape #3, which is visible in for instance USA where Randall lives should be seen like #4 in the southern part of South America, also at night! However, because the light portion of the moon is illuminated by sunlight (whether or not the moon is in the sky at the same time as the sun), the light side of the moon will always be facing towards the sun. If the moon is in the night sky, the sun must be somewhere "below" the horizon on the other side of the Earth. Thus, at night, the light portion of the moon must always be on the half of the moon that faces the horizon; However, in the case of twilight after sunset and shortly after (like the example painting), due to the [https://www.academia.edu/7848972/THE_MOON_TILT_ILLUSION moon tilt][http://www.seas.upenn.edu/~amyers/MoonPaper20June.pdf illusion] the bright side of the moon may appear to point up relative to an observer on the ground (although not to the extent show in the comic). But as the text from Randall points out there can be times during daytime when the orientation can go the other way. But then the background should not be black. Originally Randall wrote a different (wrong) sentence here and then corrected to the one currently explained, see [[#Trivia|trivia]] below.|| Van Gogh, {{w|File:Van Gogh - Passeio ao Crepúsculo.jpg|Landscape with Couple Walking and Crescent Moon}}
 
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|5 ||[[File:moon5a.jpg]]|| Wide crescent-like moon where the horns don't connect through a diameter || <font color="red">Not normal</font>||  rowspan="2" | Only possible during a lunar eclipse (#1 only, dubious) or a solar eclipse (bright part is the Sun) || This is only possible during a partial solar eclipse or the start of an annular eclipse (in which cases the lit portion is not the moon, but the sun), or else if the Earth is casting its partial shadow on the Moon, a penumbral lunar eclipse. Randall labels the lunar eclipse "dubious", since the shadow during penumbral eclipse would be much lighter than shown here, in fact barely visible as a slight darkening of the Moon's surface. The Earth's shadow, being very large, would also likely cast a less-rounded edge than depicted here. ||  
 
|5 ||[[File:moon5a.jpg]]|| Wide crescent-like moon where the horns don't connect through a diameter || <font color="red">Not normal</font>||  rowspan="2" | Only possible during a lunar eclipse (#1 only, dubious) or a solar eclipse (bright part is the Sun) || This is only possible during a partial solar eclipse or the start of an annular eclipse (in which cases the lit portion is not the moon, but the sun), or else if the Earth is casting its partial shadow on the Moon, a penumbral lunar eclipse. Randall labels the lunar eclipse "dubious", since the shadow during penumbral eclipse would be much lighter than shown here, in fact barely visible as a slight darkening of the Moon's surface. The Earth's shadow, being very large, would also likely cast a less-rounded edge than depicted here. ||  
 
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|-
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|6 ||[[File:moon6.jpg]]|| Narrow crescent-like moon where the points don't connect through a diameter || <font color="red">Not normal</font> || This situation is even harder to create than the previous one - unlike the previous example, here the diameter of the entire shadow is clear, and is too small for the Earth's shadow in a lunar eclipse. A huge ''Independence Day'' spaceship (as per the Title text) might be the right size. It does however resemble a partial {{w|annular eclipse}} if you imagine that the black area is the moon covering up the white sun. || {{w|File:AlcoholicBluesCoverVonTilze.jpg|Alcoholic Blues}}.  Van Gogh, {{w|File:Van Gogh - Starry Night - Google Art Project.jpg|Starry Night}} but turned the other way.
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|6 ||[[File:moon6.jpg]]|| Narrow crescent-like moon where the points don't connect through a diameter || <font color="red">Not normal</font> || This situation is even harder to create than the previous one - unlike the previous example, here the diameter of the entire shadow is clear, and is too small for the Earth's shadow in a lunar eclipse. A huge ''Independence Day'' spaceship (as per the Title text) might be the right size. It does however resemble a partial {{w|annular eclipse}} if you imagine that the black area is the moon covering up the white sun. || {{w|File:AlcoholicBluesCoverVonTilze.jpg|Alcoholic Blues}}.  Van Gogh, {{w|File:Van Gogh - Starry Night - Google Art Project.jpg|Starry Night}}, but turned the other way.
 
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|7 ||[[File:moon7.jpg]]|| Crescent moon blocking stars|| <font color="green">Normal</font> || Looks OK || Reality (as in image 3) with stars shown around the moon, but not any inside the sphere of the sky that would be blocked by the dark (but still present) side of the moon. (See [[#Trivia|trivia]] below though). ||
 
|7 ||[[File:moon7.jpg]]|| Crescent moon blocking stars|| <font color="green">Normal</font> || Looks OK || Reality (as in image 3) with stars shown around the moon, but not any inside the sphere of the sky that would be blocked by the dark (but still present) side of the moon. (See [[#Trivia|trivia]] below though). ||
 
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|8 ||[[File:moon8.jpg]]|| Crescent moon with stars between horns || <font color="red">Not normal</font> || There's either a hole in the Moon or a nuclear war on its surface || Many people (including artists) seem to forget that the dark portion of the moon is still a solid object that we cannot see through.[https://imgur.com/S30fuOj][https://s-media-cache-ak0.pinimg.com/236x/a7/7d/4a/a77d4ae9e3549e36edd350246d33700c.jpg] If stars are visible, there are either one or more holes in the moon, or the light-source is actually on the moon, such as nuclear explosions. As the {{w|Star and Crescent}}, the image is sometimes considered a symbol of Islam, although it's relatively recent and there's no traditional basis for putting the star ''between'' the horns - as originally used on the Flag of Turkey, the star appears in a realistic position. The flags of Algeria, Tunisia and some other countries show the star in the dark part of the moon. In the first Edwin Blashfield, {{w|File:Edwin Blashfield - Spring Scattering Stars.jpg|Spring Scattering Stars}} a God is standing on the moon throwing stars down, but then these stars are actually in front of the moon and are good. Nothing in the image suggest that stars can be seen through the dark part of the moon. Also, the {{w|DreamWorks Animation}} logo shows no stars. Although both show persons sitting on the seal, this is thus also clearly not an effort to make it look real. But in neither case stars can be seen in the moon. This is also the case for the live [https://youtu.be/xPpy8mYHQps?t=11 DreamWorks logo from movies]. Here there are stars in the background, but they are not inside the moon as [https://www.explainxkcd.com/wiki/images/f/f5/1738_Moon_Shapes_DreamWorks_logo_With_Moon_Circle.PNG can be seen here]. || An example can be found in the [https://www.explainxkcd.com/wiki/images/2/26/1738_Moon_Shapes_Mole_Car_Moon_With_Stars_Inside.png image on the last page] of [https://www.amazon.co.uk/How-mole-got-his-car/dp/B0000CKRB4 How mole got his car] with the {{w|Mole (Zdeněk Miler character)|Mole}} from the carton series by {{w|Zdeněk Miler}}. This is not just showing the stars inside from the last shape, but also the type of moon shown in the sixth image.
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|8 ||[[File:moon8.jpg]]|| Crescent moon with stars between horns || <font color="red">Not normal</font> || There's either a hole in the Moon or a nuclear war on its surface || Many people (including artists) seem to forget that the dark portion of the moon is still a solid object that we can not see through.[http://imgur.com/S30fuOj][https://s-media-cache-ak0.pinimg.com/236x/a7/7d/4a/a77d4ae9e3549e36edd350246d33700c.jpg] If stars are visible, there are either one or more holes in the moon, or the light-source is actually on the moon, such as nuclear explosions. As the {{w|Star and Crescent}}, the image is sometimes considered a symbol of Islam, although it's relatively recent and there's no traditional basis for putting the star ''between'' the horns - as originally used on the Flag of Turkey, the star appears in a realistic position. The flags of Algeria, Tunisia and some other countries show the star in the dark part of the moon. In the first Edwin Blashfield, {{w|File:Edwin Blashfield - Spring Scattering Stars.jpg|Spring Scattering Stars}} a God is standing on the moon throwing stars down, but then these stars are actually in front of the moon and are good. Nothing in the image suggest that stars can be seen through the dark part of the moon. Also the {{w|DreamWorks Animation}} logo shows no stars. Although both show persons sitting on the seal, this is thus also clearly not an effort to make it look real. But in neither case stars can be seen in the moon. This is also the case for the live [https://youtu.be/xPpy8mYHQps?t=11 DreamWorks logo from movies]. Here there are stars in the background but they are not inside the moon as [http://www.explainxkcd.com/wiki/images/f/f5/1738_Moon_Shapes_DreamWorks_logo_With_Moon_Circle.PNG can be seen here]. || An example can be found in the [http://www.explainxkcd.com/wiki/images/2/26/1738_Moon_Shapes_Mole_Car_Moon_With_Stars_Inside.png image on the last page] of [https://www.amazon.co.uk/How-mole-got-his-car/dp/B0000CKRB4 How mole got his car] with the {{w|Mole (Zdeněk Miler character)|Mole}} from the carton series by {{w|Zdeněk Miler}}. This is not just showing the stars inside from the last shape, but also the type of moon shown in the sixth image.
 
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:[Caption above the panel:]
 
:[Caption above the panel:]
 
:'''Interpreting the shape of the moon in art'''
 
:'''Interpreting the shape of the moon in art'''
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:[The left part of the panel shows a two-column chart is shown with labels above the columns. The left side shows the moons shape as white on a black square. These types of moons could be seen in certain art pieces. The right side saying whether this is normal or not as indicated with a green check mark or a red X. Right of the second column there are explanations of why the specific type of moon is marked as it is and what it could be called or how it could be possible even with the red X. The upper three moons have one common explanation as indicated with a bracket that covers all three with the text on the middle part of the bracket. Similarly moon five and six also have a bracket and only one explanation.]
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:[The left part of the panel shows a two column chart is shown with labels above the columns. The left side shows the moons shape as white on a black square. These types of moons could be seen in certain art pieces. The right side saying whether this is normal or not as indicated with a green check mark or a red X. Right of the second column there are explanations of why the specific type of moon is marked as it is and what it could be called or how it could be possible even with the red X. The upper three moons have one common explanation as indicated with a bracket that covers all three with the text on the middle part of the bracket. Similarly moon five and six also have a bracket and only one explanation.]
 
:Shape Normal?
 
:Shape Normal?
  
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* [[Randall]] changed the text for the fourth moon shape the next day from "Only possible during a solar eclipse" to "Not possible at night".
 
* [[Randall]] changed the text for the fourth moon shape the next day from "Only possible during a solar eclipse" to "Not possible at night".
 
** The original can be found [https://web.archive.org/web/20160926101411/http://xkcd.com/1738/ here].
 
** The original can be found [https://web.archive.org/web/20160926101411/http://xkcd.com/1738/ here].
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* [[File:moon7a.jpg]] The image of the crescent moon blocking the stars is slightly wrong because there are still lights on the surface of the moon.
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* [[File:moon7a.jpg]] The image of the crescent moon blocking the stars is slightly wrong, because there are still lights on the surface of the moon.
  
 
{{comic discussion}}
 
{{comic discussion}}

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