But is there really a \u201cdark side\u201d of the Moon, or is that just a flowery expression that doesn\u2019t actually apply in reality? That\u2019s what Graeme Cree wants to know, posing the following inquiry to me:<\/p>\n
\u201cOf course, there is no literal \u201cDark Side of the Moon\u201d. There\u2019s a side that faces permanently away from the Earth, but no side that faces permanently away from the Sun. \u201cDark Side\u201d is a metaphorical way of saying Unknown Side\u2026 Astrophysicist Ethan Siegel might get a kick out of this. He\u2019s probably dealt with the same misconception himself, and can probably answer the question of whether or not anybody still calls it the dark side.\u201d<\/p>\n
Although \u201cdark side\u201d did originally mean \u201cfar side,\u201d and the \u201cfar side\u201d is only slightly darker than the \u201cnear side,\u201d there really is a \u201cdark side\u201d to the Moon. Here\u2019s what we\u2019ve discovered so far.<\/p>\n
![\"Illustration](\"https:\/\/www.newsbeep.com\/il\/wp-content\/uploads\/2025\/11\/Mond_Grafik.svg.png\")
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Although one half of the Moon, only, is ever illuminated by the Sun, both the portion of the Moon that\u2019s illuminated by the Sun and the illuminated portion that\u2019s visible from Earth change over the course of a lunar month. A complete cycle, from new phase to new phase, defines the length of a lunar month. Note that, from someone\u2019s perspective on the Earth-facing (near) side of the Moon, it\u2019s never truly dark, as either the Earth or Sun (or both) is always shining light on the Moon.\n<\/p>\n
Credit<\/a>: Horst Frank & Nethac DIU\/Wikimedia Commons<\/p>\n To be clear, there is a real and important difference between something that\u2019s \u201cobscure to us,\u201d like the far side of the Moon (as viewed from Earth), and something that is an actual \u201cdark side,\u201d where the Sun doesn\u2019t shine on it. When it comes to the near side of the Moon \u2014 the side that always faces us \u2014 we know that there is no dark side there because, even with the naked eye, we can observe that there isn\u2019t. As the Moon goes through its phases every month, and as its phases shift with respect to apogee (when the Moon is farthest from Earth) and perigee (when the Moon is closest to Earth), the entirety of the near side gets illuminated by direct sunlight for about two continuous weeks in a row, followed by two weeks of darkness.<\/p>\n Even during those dark periods, however, the Moon is never truly dark, as it\u2019s illuminated by the reflected light from the Earth: Earthshine. Just as the Moon goes through the full gamut of phases \u2014 from new to full and back to new again \u2014 as seen from the Earth, the Earth does the same thing as seen from the Moon. A \u201cnew Earth\u201d corresponds to a \u201cfull Moon,\u201d however, so that the only time there isn\u2019t a bright Earth shining in the near side of the Moon\u2019s sky is when the Sun is shining on the entirety of the Moon\u2019s near side. In a sense, it\u2019s never dark on the near side of the Moon, because the Moon is always illuminated by either the Earth or the Sun or both; there\u2019s never a moment where it\u2019s darker than that.<\/p>\n Although the Moon is tidally locked to the Earth so that the same side always faces our planet, the fact that the Moon\u2019s orbit is elliptical and follows Kepler\u2019s laws of motion ensures that it appears to rock back-and-forth while growing and shrinking in apparent size over the course of a month: a phenomenon known as lunar libration. Overall, 59% of the total lunar surface, not 50%, is visible from Earth over time, and eclipses can occur during the new or full phase if the Moon happens to be passing through the Earth-Sun plane at that time.\n<\/p>\n Credit<\/a>: Tomruen\/Wikimedia Commons<\/p>\n However, even if you take into account the effect of lunar libration (as illustrated above), which is the apparent \u201crocking\u201d of the Moon as it both:<\/p>\n rotates on its axis (which it does at a constant speed),<\/p>\n and revolves around the Earth (which it does at a maximum speed near perigee and a minimum speed near apogee),<\/p>\n we find that we can only see approximately 59% of the Moon\u2019s area from our vantage point on Earth. The remaining 41% of the lunar surface can never be seen from Earth; it\u2019s always on the \u201caway-facing\u201d side, which is known as the far side.<\/p>\n For centuries and millennia, that opposite side of the Moon remained obscure. Whatever was located there was completely \u201cdark\u201d to us, as it couldn\u2019t be glimpsed from anywhere on Earth\u2019s surface: where humanity was trapped by the force of gravity for so long. However, beginning in the mid-20th century, the development of rocketry led to our earliest spaceflights. Sputnik 1 was launched by the Soviet Union in 1957, becoming the first spacecraft to successfully orbit the Earth, and launching what\u2019s today known as the space race. Just two years later, in 1959, the USSR launched Luna 3, which took a total of 29 photographs of the lunar far side, covering 70% of the area that had previously been invisible to humans. For the first time, we had knowledge of the Moon\u2019s other side.<\/p>\n This photograph is the first view of the lunar far side ever acquired by humanity, as the USSR\u2019s Luna 3 spacecraft flew past the Moon\u2019s far side and snapped a series of more than 20 pictures, covering over 70% of the far side\u2019s surface. Subsequent views have been far more informative, illuminating the lunar far side over the past 66 years in a way that would have amazed and delighted all the humans who came before the advances that made this possible.\n<\/p>\n Credit<\/a>: Union of Soviet Socialist Republics (USSR)<\/p>\n To be certain, there were several surprises in store for us when we began to look, over time, with greater resolution and fuller coverage of both hemispheres of the Moon. Whereas the Moon\u2019s near size has a large portion of it covered by deep, dark \u201cseas\u201d (or maria) where very few craters reside, the far side only has one prominent, small deep one and one large shallow one. The far side\u2019s average elevation is a few kilometers greater than the near side\u2019s average elevation. And there\u2019s a very interesting and compelling theory that the chemical composition of the far side ought to be different from that of the near side<\/a>: a theory we\u2019re on the brink of testing now that we\u2019ve returned samples from the Moon\u2019s far side as well.<\/p>\n However, we were able to confirm something else with superior coverage of the Moon\u2019s surface along with higher-resolution imaging: everywhere on the far side, just as is the case on the near side, appears to get illuminated by the Sun at some point during each lunar month. Most locations, just like on the near side, alternate between spending two weeks in darkness and two weeks in direct sunlight. The only major difference, for most of the lunar surface on the far side, is that there\u2019s no \u201cEarth\u201d to shine in their skies: either during the day or to illuminate the lunar night. The lunar nights are darker on the far side of the Moon, but the far side is, during the day, just as light as the near side.<\/p>\n This two-faced mosaic from NASA\u2019s Lunar Reconnaissance Orbiter shows the near side (left) and the far side (right) of the Moon with modern technology. By looking at the ratios and sizes of craters found on the Moon with respect to the age of that portion of the Moon, Mars, Mercury, and Earth, we can learn how cratering rates have varied over the Solar System\u2019s history. Now, with our first samples from the lunar far side having been returned to Earth, we might finally learn more about the Moon\u2019s ultimate origins.\n<\/p>\n Credit<\/a>: NASA\/GSFC\/Arizona State University<\/p>\n So when it comes to the \u201cdark side\u201d of the Moon, if you mean the \u201cfar side\u201d of the Moon, you should say \u201cfar side\u201d rather than \u201cdark side.\u201d The only way that the far side is darker than the near side comes from the lack of having a large, bright, reflective Earth in the sky, especially during the lunar night, when the Sun isn\u2019t shining at all. It\u2019s also true \u2014 but not quite the point \u2014 that the far side is much darker and quieter in one particular set of wavelengths of light: in the radio band.<\/p>\n In fact, the far side of the Moon is arguably the quietest place in the entire Solar System, for the exact reason that it never receives Earthshine: it\u2019s always facing away from the Earth. Since nearly all of the Solar System\u2019s radio signals are generated by either the Earth or the (radio-loud) Sun, \u201cnight on the Moon\u2019s far side\u201d is the most radio-quiet place of all. This is why scientists have long hoped to build an enormous lunar radio telescope in a far-side crater, because it\u2019s the one place that has the lowest noise floor in all the Solar System, and it\u2019s right here in Earth\u2019s backyard.<\/p>\n The greatest danger to the radio-quiet status that the lunar far side has is actually part of humanity\u2019s plans for human exploration of the Moon: to place an array of radio-loud satellites in lunar orbit. If we actually do this, then the one way the Moon\u2019s far side actually is dark \u2014 in radio light \u2014 will disappear.<\/p>\n Constructing either a very large radio dish, perhaps in a lunar crater, or alternatively an array of radio telescopes, on the far side of the Moon, could enable unparalleled radio observations of the Universe, including in the all-important 21 centimeter range, both nearby and across cosmic time. The ability to map out where neutral hydrogen has newly formed within the past ~20 million years would advance our understanding of cosmic history like nothing else.\n<\/p>\n Credit<\/a>: Saptarshi Bandyopadhyay<\/p>\n However, it isn\u2019t true that there\u2019s no such thing as a \u201cdark side\u201d of the Moon. In terms of our common understanding, \u201cdark\u201d means that it\u2019s shielded from the Sun, and never receives direct sunlight. On the Moon, that\u2019s all it takes. Because there is no atmosphere at all:<\/p>\n no air molecules to scatter and reflect sunlight,<\/p>\n no lunar dust that gets kicked up and reflects scattered light,<\/p>\n no clouds, hazes, or other particles that reflect light,<\/p>\n and no medium to reflect direct sunlight that might fall on other, more faraway portions of the Moon\u2019s surface,<\/p>\n simply being in a region of permanent shadow, that never receives direct sunlight itself, would equate to being in a \u201cdark place\u201d on the Moon.<\/p>\n It might not take up an entire hemisphere \u2014 or \u201cside\u201d \u2014 of the Moon, but there actually are several locations on the Moon that do meet these criteria: the permanently shadowed craters at and sufficiently close to the lunar north and south geographic poles. Here on Earth, our north and south poles spend six months in continuous light followed by six months in continuous darkness, and that\u2019s due to our large (roughly 23.5\u00b0) axial tilt. When one polar hemisphere is tilted toward the Sun, it\u2019s always illuminated; when it\u2019s tipped away, it\u2019s never illuminated.<\/p>\n However, even though the Moon revolves around the Earth, its axial tilt with respect to the Sun is extremely small<\/a>: just 1.54\u00b0, or only about 6-7% as great as Earth\u2019s much more pronounced axial tilt.<\/p>\n Whereas the Earth has a significant axial tilt with respect to the Sun of 23.44 degrees, the Moon\u2019s inclination is much less severe: at just 1.54 degrees. (The difference between the 6.68 and the 5.14 degree figures shown in the diagram here.) This small axial tilt, combined with the depth of craters with high-rimmed crater walls on the Moon, enables the existence of true locations of darkness.\n<\/p>\n Credit<\/a>: NASA<\/p>\n This means that, at or near the lunar poles, a sufficiently large and deep depression in the ground \u2014 including just a regular old impact crater \u2014 will prevent any and all sunlight from ever striking the low points of that depression. When the lunar pole you\u2019re at is tipped toward the Sun, you only need to remain a couple of degrees below the rimmed wall of that depression (again, most craters have high walls) and sunlight will never directly strike you. When the lunar pole you\u2019re at is tipped away from the Sun, it\u2019s even easier. This makes not just the poles themselves, but the sufficiently deep and expansive craters within 5-to-even-10\u00b0 of the poles good candidates for being dark.<\/p>\n In planetary science, we don\u2019t often refer to these regions as the \u201cdark side of the Moon,\u201d but they are indeed some of the darkest places within the Solar System that one can venture to. We usually refer to them as permanently shadowed craters, and note that they behave as \u201ccold traps,\u201d which warrants further explanation. Whereas the majority of the Moon\u2019s surface is inhospitable to volatile molecules, such as ices, persisting for any meaningful duration of time, because direct sunlight will heat them up and sublimate them into a vaporous state, these \u201ccold traps\u201d represent excellent places for volatile ices, should they ever enter these dark places, to persist indefinitely far into the future.<\/p>\n These Lunar Reconnaissance Orbiter mosaics of the North and South poles of the Moon showcase several candidate craters whose insides likely never receive direct sunlight. The walls of these craters are candidates for being peaks of eternal light, while the insides of the craters never rise above temperature of 100 K, serving as \u201ccold traps\u201d for volatile ices and more.\n<\/p>\n Credit<\/a>: NASA\/GSFC\/Arizona State University<\/p>\n The north pole of the Moon does have plenty of craters that appear to be good candidates for being permanently shadowed, or dark, in precisely this fashion. Observations at radio frequencies that were conducted as far back as the 1990s indicate that there are likely reservoirs of volatiles, including water-ice, present within at least some of those craters. Many have long speculated that if you:<\/p>\n set up solar panels around the crater rims,<\/p>\n create a pressurized environment either inside or outside of the crater,<\/p>\n and gather\/mine the ice \u2014 which will be more like a dirty slushball, most likely \u2014 inside of those permanently shadowed craters,<\/p>\n you\u2019d be able to perform all sorts of tasks, including tasks toward creating habitable environments, without having to bring your own materials, such as water and air, from Earth.<\/p>\n However, the south pole of the Moon is an even better location than the north pole of the Moon in this regard, with very large prominent craters (such as Shackleton crater<\/a>) remaining in permanent shadow. Although a layer of lunar regolith<\/a>, or Moon dust\/soil\/rocks, likely covers whatever exists in the \u201ccold traps\u201d within these craters, direct observations indicate that the temperatures inside the crater never rise above a maximum 100 K (-173 \u00b0C\/-279 \u00b0F), meaning that not only water ice, but dry ice (carbon dioxide) and possibly even methane ice could persist, long-term, within these craters.<\/p>\n This rendering of the South Pole area of the Moon shows 13 candidate landing regions for Artemis III. Each region, shown in blue, is approximately 225 square kilometers, with some of them atop \u201cpeaks of eternal light\u201d that always receive sunlight, or that border permanently shadowed craters on the Moon.\n<\/p>\n Credit<\/a>: NASA<\/p>\n These permanently shadowed regions are as close as one can actually get to a true \u201cdark side\u201d of the Moon. At both the north and south lunar poles, these coveted pieces of lunar real estate are likely the perfect locations to stake out and claim if one wants the most resource-rich regions of the Moon for themselves. The combination of ancient material that\u2019s likely found within these craters (and nowhere else on the Moon), the fact that they have access to continuous sunlight at the top of the crater walls (rather than having to reckon with two continuous weeks of darkness), and where they\u2019ll be able to either communicate with Earth (at the crater wall tops) or be shielded from Earth (within the crater) makes them unlike anyplace else on the Moon.<\/p>\n Even though there are treaties prohibiting \u201cownership\u201d of any locations on the Moon for any public, private, or national entity, there is a loophole that several nations are racing to exploit: the ability to declare a keep-out zone, for safety reasons, if one is conducting nuclear activity on the Moon<\/a>. This is what\u2019s behind the race to build a nuclear reactor on the Moon<\/a>:<\/p>\n These locations are suspected to be highly sought after as a means to begin experimenting with human colonization of other worlds here in the 21st century, with nuclear power plants on the Moon providing justification for activity that would otherwise violate the international law of the Outer Space Treaty.<\/p>\n Humanity has long dreamed of establishing a robust and continuous presence on another world, such as the Moon or Mars. One of the keys to such a successful colony would be the continuous generation of power, with nuclear power plants remaining a prime, and arguably our best, option. However, claiming the real estate of peaks of eternal light and permanently shadowed craters for one\u2019s own interests, whether national or business interests, is likely the true motivation behind the desire for nuclear power plants on the Moon.<\/p>\n![\"lunar](\"https:\/\/www.newsbeep.com\/il\/wp-content\/uploads\/2025\/11\/Lunar_libration_with_phase_Oct_2007_continuous_loop.gif\")
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