Lunar Observatories

Humanity’s striving to reach the Moon, in fact and fiction, has had many motivations. Amongst them, pretty much from the beginning, has been a desire driven by our overwhelming urge to understand the universe around us - to see the stars ever more clearly. Here I take a look at the science and SF of lunar observatories.

Adventurous Observatories 

The existence of an astronomical observatory on the Moon was an assumed feature of lunar settlements from early in the pulp era of science fiction. 

The 1930s were an era when tales of adventure, fights with animals or primitives and rescue of helpless women were common in science fiction, and known as planetary romances. An interesting example is Monsters of the Moon by Francis Parnell (appearing in Tales of Wonder, January 1937). The hero of this tale, Harry Johnson, is a junior astronomer at the Lunar Observatory:

“Beside him the enormous telescope sloped up like some monstrous cannon to the glass dome of the observatory, towering around him like a gigantic soap bubble.”

Alone on watch in the observatory, he spies a herd of lunar ‘flying cows’ bearing down on a trapped girl, Mary, the daughter of an ice mining chief engineer. After crashing his vehicle, wrestling moon snakes, rescuing the damsel and falling into an undiscovered cave, the two of them are eventually rescued just as their suits begin to fail. On discovering that the observatory dome was smashed by the cattle stampede, Harry fears his career on the Moon is over before discovering that the ice found in the newly opened cave has made him rich. Admittedly astronomy doesn’t really feature in the story, but it is still interesting in the presumption that an astronomical telescope would be amongst the first structures to be built in a nascent lunar settlement.

Moving forward into the postwar race for space, the role of lunar observatories becomes more prominent. Published in 1949, Charles L Harness’s novel The Paradox Men describes a future society in which America has become a police state and slavery has been reinstated. Against this background, a group of intellectuals and rebels have formed the Society of Thieves in order to steal from the wealthy and use the profits to free slaves. Amongst them is Alar, a man with amnesia and a surprising past. As a result of that past, he finds himself pursued to the Moon, and to the settlement Selena which exists purely to serve a great lunar observatory. This is home to a “two hundred meter reflector” - a vast telescope which Harness describes as powerful enough to see all the way around a closed universe. The result of this is that the gigantic mile-across hologramatic map used to visualise the telescope’s observations actually shows the Local Group and our own Milky Way as seen from outside.

A two hundred meter diameter telescope is an order of magnitude larger than any extant or currently planned facility in the real world, and would likely be impossible on Earth without sagging under its own weight. Its use from here would also be severely limited by both light pollution and, more importantly, the distortion effects of Earth’s atmosphere. While it might be possible to construct such a facility on the Moon without immediate collapse, the scale of the structure required might be prohibitive to transport from Earth’s surface and challenging to construct in situ without a major lunar infrastructure already in place.

In addition, to the best of our current knowledge, the Universe we inhabit is flat rather than open or closed - this means that, regardless of telescope power, we will never be able to look outwards and see our own location from the outside as theorized in the 1950s, and in this story. The use of immersive hologram mapping in this story is nonetheless also interesting. We are yet to be able to project holograms in three dimensions, as so beloved of science fiction, but virtual reality (using glasses less unwieldy than the original headsets) and enhanced reality (seen through a smartphone camera) are increasingly being used for visualisation and science communication regarding astronomical images and modelling. It’s not beyond the realms of possibility that the use of VR to inspect a modelled system from all directions (as the vast hologram is used in The Paradox Men) will become a tool in academic research in future.

Amongst the most dramatic events to occur at a science fictional lunar observatory are described in Arthur C Clarke’s Earthlight (published as a novella in 1951 and expanded into a novel in 1955). This story is set against a backdrop of rising tension between authorities on Earth and the settlers who have colonised other regions of the Solar System and formed an Outer Planets Federation. The personnel of a large lunar observatory in the Plato Crater are puzzled by a long and delicate preparedness drill to practice removing their precious thousand-inch (25m) mirror to the safety of an underground chamber:

With infinite slowness the great disk of quartz, that had cost a hundred million to make, was lowered from its cell to the strange vehicle beneath the telescope. The ninety-foot-wide truck sank visibly on its scores of tiny balloon tyres as it took up the weight of the immense mirror. Then the hoisting gear was released and with a purr of motors the truck and its precious cargo began to move slowly down the ramp leading to the resurfacing room.

It was a breathtaking sight. The men scattered over the floor were utterly dwarfed by the lattice work of the telescope towering hundreds of feet above them. And the mirror itself, over eighty feet in diameter, seemed like a lake of fire as it reflected the glare of the overhead lights. When at last it had left the room it was as though dusk had suddenly fallen. 

A surge in nearby rocket activity affects observations and it becomes clear that this is a direct consequence of the discovery of uranium - a resource closely controlled by Earth but urgently needed by the Federation - on the Moon. The arrival of an Earth government agent amidst the personnel of the lunar observatory, and then of armed spaceships, indicates that the Moon has become the front line in a rapidly escalating conflict. The story climaxes with an all out nuclear battle - one of few in Clarke’s writing. The personnel of the observatory survive but are left questioning whether their efforts supported the right side in the conflict.

Amongst other aspects of practical astronomy captured by Clarke, it’s interesting that he highlights a seldom mentioned practicality. Telescope mirrors on Earth must periodically be resurfaced due to the effects of time, dust and atmosphere having a corrosive effect on the nanometre-perfect surface required for accurate astronomy. Most major observatories have a resurfacing room, but unmounting and remounting the telescope mirrors is a major operation which is undertaken at rare intervals. On the Moon, where Clarke describes his telescope dome as usually being open to vacuum, the effects of atmosphere might be less significant but damage from particles of lunar regolith (the hard and angular dust on the Moon’s surface) might be worse. Either way, the existence of a resurfacing room in the caverns beneath the telescope (which also house and protect the astronomers) permits a mirror described as “the human race’s most valuable single possession” to be saved from the catastrophic effects of battle.

Opportunities at Observatories

An important role of science fiction, particularly that aimed at juvenile readers, is to explore the stresses, surprises and opportunities of adolescence. Coming of Age stories in any setting explore the possibilities of engaging with a wider world beyond the family. In science fiction these possibilities extend beyond Earth-bound horizons.

Jack Vance’s Vandals of the Void (novel, 1953) is an archetypal example of the subgenre of rocket adventure fiction aimed at young readers. Dick Murdock is a fourteen year old, born on a colony on Venus and, at the start of the novel, en route to join his father (who is head of the Lunar Observatory) and to begin his studies in astronomy. However the space lanes are being preyed upon by space pirates, and, after a close brush, Dick arrives on the Moon already wary of spies and suspicious of his companions. Between lunar prospecting excursions, he hears strange coded radio messages and begins to suspect that the death of the last observatory director was not an accident. Unsurprisingly, Dick’s curiosity leads him in deadly danger and onto the front line between space pirates led by the mysterious Basilisk and the newly commissioned and under equipped Space Navy. 

Astronomy may not be young Dick’s best destiny but it nonetheless provides an interesting and rich background to the story. The majority of the story is set in and around an internationally-staffed observatory which appears to be the only human settlement on the Moon after mining efforts and a weapons platform were both abandoned as unprofitable. As Dick discovers, catalog numbers of stars are also the key to the pirates’ code. The lunar observatory itself hosts a thirty-six feet telescope (unthinkable on Earth at the time) which is described as looming over it like an insect in the earthlight. This telescope is notable for two key features.

First, its camera was operated from a cage suspended at the telescope prime focus - i.e. directly above the mirror. This was common for large telescopes at the time, since the prime focus is best for stable imaging as the light has gone through fewer reflections and distortions. With improved mirror technologies and active control systems, the prime focus is rarely used today, with the light more often reflected downward by a secondary mirror before being collected. Where it is used now, the camera is typically operated remotely, rather than very cold astronomers being suspended in vertiginous cages as in years past. As it happens, the prime focus cage proves a particularly nasty trap in the story.

Secondly, Vance (and hence his characters) gives some thought to how a mirror that size might be made possible on the Moon. We’re told that:

“The engineers employed a very ingenious process; the mirror is actually solid quicksilver. It was poured as a liquid into the rim casing, which was then rotated very slowly. Centrifugal force pressed the quicksilver out against the rim of the casing in a perfect uniform curve. After a moment the quicksilver congealed, froze into shape."

"You could build a mirror as big as you wanted— any size!" marveled Dick.

Dr. Murdock nodded. "Theoretically, yes. Killing the vibration is the hardest part, since the slightest tremor flaws the mirror. Every last little rasp and drag has to be eliminated; the quicksilver is even shielded from dust. The casing pivoted on a piston only an inch in diameter in a pool of oil; the torque is supplied magnetically. As a result, we have the most powerful instrument human ingenuity can conceive.”

Liquid mirror telescopes - most commonly using mercury - were proposed by Isaac Newton and have been demonstrated a number of times astronomically, although their toxicity and gyroscopic effects due to the rotation of the Earth limit their usefulness. Both of these problems would be reduced, although not eliminated, on the Moon or in space and related ideas have been and continue to be explored by the astronomical community.

Another coming of age story, seen from a different perspective, can be found in Holiday on the Moon, a short story written by Arthur C Clarke. Appearing in Heiress magazine in 1951, it was originally published under the pseudonym Charles Willis, as Clarke feared that writing for a girl’s magazine would negatively affect his credibility as a science fiction author. Again the protagonist is visiting their father who is director of the Lunar Observatory, but in this case the story focuses on Daphne, a (rather annoying) teenage girl. On arriving, she finds that the staff of the observatory is not as expected:

Daphne had always assumed - although she couldn’t have said why - that astronomers were usually old men with beards and far-away expressions caused through too many hours of looking through telescopes. (Daddy was, of course, an exception - he always was.)
She soon found, however, that none of the Observatory staff fitted this description at all. Most of them were in their twenties or thirties, and almost half of them were women.

The staff are pursuing observations of a supernova. The new role models, together with the skills she develops during the trip, opens Daphne’s eyes to the idea that her horizons are broader and offer more excitement and fulfilment than was apparent in her conventionally Earthbound life. The story ends with her family returning to Earth,

But one day, Daphne knew, she would return. This world, not Earth, would be her home. At last she had found her ambition, although as yet she had breathed a word of it to no one. There would be years of study ahead, but in the end she would join the quest for the secrets of the stars.

A different relationship between adolescent and father is found in Growing Up Weightless (novel, 1993) by John M Ford. Here a group of teenagers raised in a lunar colony rebel against parental authority by planning and undertaking a trip across the Moon from their home at Copernicus via rail to an observatory at Tsiolkovsky crater on the lunar farside. This hosts a mixture of optical and other telescopes:

They had tea, and the scientists showed the team around the Institute, apologizing that it was mostly data machines, not real telescopes; a big window looked out on one of the medium-sized radio telescopes (the largest one was inside Tsiolkovsky crater itself), though in the Farside night it was just some colored marker lights against the blacked-out ground, below the stars. It was still beautiful.

Computers and data banks are fundamental to radio astronomy, and it makes sense that these were the most visible equipment from within the base, while the telescopes (in vacuum outside) are operated remotely. Ford also notes the impact of even the sparse lunar atmosphere on the optical telescope and also the intensity of work required during the two week lunar night relative to the (less usable) day:

“When it’s dark on Tsio, people work until they notice they’re asleep and half-starved at the telescopes!”

Although the very sparse atmosphere on the Moon is too thin to thoroughly scatter light as Earth’s does during daytime, it is certainly sufficient that observations would be much less useful and less sensitive when the Sun is above the horizon. The radio telescopes too would be impacted by the bright radio source the Sun represents, when it is no longer being shielded by the Moon’s bulk. The focus in this story is on the self-discovery of the protagonist Matt rather than astronomical discovery, but the observatory is representative of the outward-looking urge felt by youth growing up bound by parental protection and rules… even those growing up on the Moon.

Academia at Observatories

Academic research is the focus of an interesting short story “The Cosmic Blinker” by Eando Binder (published in the magazine Science Fiction+ in May 1953 [1]). This focuses on a group of astronomers based at a lunar observatory. Amongst them is one who has spent a career observing a variable star in the galaxy M81. This had been known since the 20th century (5000 years in the past of the story) to vary erratically rather than pulsing with a predictable pattern like other variable stars. The characters realise that this might be an encoded message, and the full resources of the lunar observatory and its computer are dedicated to decoding the signal… with a dismaying result.

In fact, the variable source, described in the story as being first detected in 1950, appears to have been what we now recognise as the central Seyfert nucleus of this active galaxy. Now known to be an accreting supermassive black hole, these erratically varying objects were not understood at the time Binder was writing. However the distance to M81 - leading the astronomers in the story to wonder at the importance of a signal intended to travel for millions of years before detection - was already clear. The story is interesting in the atmosphere of intensive research and focus amongst the (exclusively male) astronomers in the lunar settlement.

A completely different form of observatory can be found in the short story Gauguin’s Questions by Stephen Baxter. The story focusses on an AI running Fra Mauro, a particle physics experiment on the near side of the Moon, who is tasked with answering the three questions posed by the artist Paul Gauguin (amongst others): Where do we come from? What are we? Where are we going?

The first of three visitors to the AI, spanning two millennia, is a scientist from the Gravitational Wave Lunar Observatory for Cosmology, or GLOC. This facility has been placed on the low vibration, low noise far side of the Moon with the goal of detecting the tiny ripples in space time associated with astronomical events. However a student tasked with looking at the signals from the perspective of SETI (the search for extraterrestrial intelligence) discovers that the Fra Mauro AI has used a carefully modulated set of vibrations on the Moon to encode its own signal to other intelligences.

The account appears in Collision: stories from the science of CERN, an anthology which pairs writers with scientists with the goal of exploring particle physics. However the use of GLOC, together with the mention of radio telescopes also located on the far side, demonstrates the close relationship between elementary particle physics and astrophysics. Gravitational wave observatories on Earth are limited by vibrations caused both by human activity and the Earth’s own seismic (i.e. earthquake) activity. The Moon has significantly less of both, although moonquakes can and do still occur due to the tidal stresses it experiences as it orbits the Sun and Earth. The idea that future human activity might also be concentrated on the lunar nearside, leaving the farside relatively quiet, is also extremely plausible.

On the Farside

While gravitational wave observatories have yet to become common in science fiction, a relatively frequent feature of lunar observatories in science fiction, and particularly radio observatories, is a location on the far side of the Moon (i.e. the face perpetually turned away from Earth [2]). The reasons for this are succinctly described in The Listening Glass by Alexis Latner (Analog, Feb 1991):

“Human activities on Earth generate an incredible amount of radio noise, swamping the faint signals from the universe. Located here, the dish and the Very Low Frequency Array are shielded from the radio noise of Earth, by the bulk of the Moon. I might add that the Moon itself is dead quiet apart from very rare rock electric discharges. No weather — no lightning, no seismic activity. For radio astronomy, there is no better place than this."

A focus on academic discovery (and its travails) also permeates this story, which describes a brand new large radio telescope dish set into a farside lunar crater, Bolton, similar to the now-defunct Arecibo telescope in design. An unfortunate accident damages the telescope (and the astronomer inspecting it) at precisely the moment when it is urgently needed to observe a rare nearby supernova. As a result the characters, operating on a shoestring budget and with the limited resources available on the lunar farside, must use ingenuity to get the facility back into operation in time to capture the emergence of the radio signal from this event.

The story is notable for its close engagement with the nature of radio astronomy, the structure and operation of radio dishes, and the pros and cons of different telescope types for this kind of work. Latner also mentions a Sino-American observatory at Yuegong base, apparently hosting optical telescopes on the edge of the nearside, and another facility on an artificial habitat at the Earth-Moon L5 Lagrange point [3]. Perhaps unsurprisingly the story was anthologised by Mike Brotherton in Diamonds in the Sky (2015) - a collection of science fiction stories that centre on astronomy.

The advantages of a farside radio observatory are also discussed by Apollo 11 astronaut Buzz Aldrin and author John Barnes in their novel Encounter with Tiber. Early in the story, a peculiar signal is detected at a wavelength of 96 metres - a part of the spectrum that is easily scattered in Earth’s atmosphere. As it happens, the protagonist is an astronaut newly arrived on the International Space Station to test the receiver for the planned Far Side Radio Telescopes (FSRT) which is under construction by a consortium of universities and research organisations.

This is intended to be robotically deployed in a near-parabolic crater on the Moon and combined with antenna elements also transported, deployed and connected by robotic missions. Communications with Earth (otherwise blocked by the Moon’s bulk) would be permitted by relays at the Earth-Moon Lagrange 4 or 5 points. However the presence of the receiver above the atmosphere, even in Earth orbit, plays a critical role in the early part of the novel when the first ever signal is received from an extraterrestrial civilisation - the people of the planet Tiber in the Alpha Centauri system. The resulting surge in space utilisation, and its new focus on recovering Tiberian relics, rather sidelines the telescope project, although a brief mention later in the book confirms that a Tsiolkovsky Observatory exists by a point a couple of decades later.

Indeed, as we’ve seen from Growing Up Weightless (discussed above), the large 184km-wide Tsiolkovskiy crater on the lunar farside (named for one of the key foundational engineers of rocketry and ultimately space travel) is a popular location for bases and particularly observatories in science fiction. Tsiolkovskiy crater also hosts an observatory in other work, such as the 2002 science fictional role playing game Transhuman Space.

Another Farside Observatory was a recurring location mentioned in Ben Bova’s Grand Tour series of novels set in an era of human solar system exploration, and it formed the main location of the 2013 novel Farside. Here the observatory is funded by the recently-independent nation of Selene, under the control of one astronomer, Prof Ulrich, who is desperate to win a Nobel Prize. He oversees two projects under construction there. Cyclops is a vast radio interferometer. But Ulrich’s focus is instead on an optical interferometer comprising three huge 100m telescopes, designed to image and characterise a newly-found, Earth-sized, habitable zone planet, Sirius C, before an Earth-funded, space-based optical interferometer can do the same. Each telescope is built around a single 100m diameter mirror, and the problems of construction and transportation of such vast mirrors forms a running plot thread through the novel. It’s unclear whether Bova really understands how an interferometer works. To construct an image, such facilities on Earth must either have enough elements (separate dishes or mirrors) that they can measure information in many orientations relative to the sky simultaneously, or must line their elements in an East-West row and rely on the rotation of Earth to twist the sky overhead, allowing information from many orientations to build up over time. With just three unit telescopes, however large, on the tidally-locked Moon, neither method works. As Bova correctly points out, however, even a single telescope that large on the lunar surface would be orders of magnitude more powerful than any telescope currently in use.

The majority of the book, though, focuses on the concerns, obsessions and relationships of the observatory personnel [4] and on the dangers both inherent to the Moon and associated with high profile projects.

 The Changing View of Lunar Observatories

Lunar astronomers feature in countless other stories spanning the history of science fiction. Clarke, Asimov and other writers such as Frederik Pohl, Robert Heinlein, Alfred Bester, Pamela Sargent and Robert Willey (a pseudonym of science communicator Willy Ley) have stories featuring astronomers who have worked at a lunar observatory, or which mention observations arising from it. These represent just the most prominent of a much larger set. Examples from audio visual media are rarer. A lunar observatory appeared in the Journey Into Space serial "The Red Planet" (Charles Chilton for BBC radio, 1954), although - as with a number of other fictions from the 1950s - it appears to be mostly used for tracking starships.

A lunar observatory also appeared in the 1973 BBC television serial Moonbase 3. This series aimed at a realistic portal of the realities of the dangers of a European moonbase, its politics, budget struggles and personal squabbles, and instead mostly managed to be depressing [5]. Amongst the activities of the base are optical telescopes, Earth-observation facilities for weather monitoring and prediction, and solar observations. The episode “Achilles Heel” also focuses on the personnel of a radio astronomy observatory at the base, working at microwave wavelengths. Their main project, CORA, suffers damage to its ‘quantum amplifier’ which appears to be just one of a string of accidents affecting the base at a time when the Moonbase 3 most needs to show success and important results. Despite mentions of a handful of substitute astronomical targets, it’s never made entirely clear what observations CORA is designed to undertake.

A common feature between Moonbase 3 and many other lunar observatory stories is the idea that lunar astronomers represent the best of the best - an elite amongst scientists. The inevitably limited size of the personnel of any moonbase, together with the expense of building a lunar telescope and the limited observing time available to any single facility, means that competition would be fierce. The leading space telescopes, Hubble and JWST, are routinely oversubscribed by a factor of ten to one or more (i.e. more than ten hours of observations are requested with strong scientific motivation for every one hour that can be observed). A single moon telescope would likely experience similar oversubscription. In examples such as Pamela Sargent’s Father (short story, 1974) and Asimov’s The Dying Night (short story, 1956), astronomy postings off-Earth are only offered to the best of the best.

In fact, space observatories at the current time or built in the future are far more likely to be uncrewed, to operate robotically, and even to be in space rather than on the lunar surface. While science fiction, scientists and indeed popular science articles in science fiction magazines, have been discussing the advantages of lunar observatories since the start of the space age, others have also been pointing out the possible disadvantages. Donald Malcolm, writing for New Worlds magazine in 1956 rhapsodised about the clarity and quality of imaging possible from the Moon, but recognised the difficulties probed by the extreme temperature swings between night and day, and by the erosion caused by micrometeorites, as well as the challenges of construction and transporting large mirrors to and across the lunar surface.

This question was also explored in Galaxy Science Fiction magazine in June 1965. Science populariser Willy Ley discussed “The Observatory on the Moon” in his long-running For Your Information series of factual articles. This traces the idea of a lunar observatory back at least to Wilhelm Beer and Heinrich von Madler in a book published in 1837. At the start of the article, Ley confidently asserted that

“Everybody is agreed on a number of fundamental thoughts, goals and conclusions. Of course the first landing will be followed by others, there will be a base on the moon — or rather a minimum of two, one speaking Russian, the other English — and there is also agreement that the main purpose of the lunar base will be research: chemistry, crystallography, electronics, metallurgy, biology and last, but by no means least, astronomy." 

Ley noted that the farside may prove vital for radio astronomy, while (in the absence of a significant lunar atmosphere) optical astronomy would benefit from the better communications offered by the nearside. The biggest issues that he identified were the challenge of making and transporting a sufficiently large mirror to the Moon and the question of whether the future facility should be pressurised or should require astronomers to don space suits to change photographic plates.

Unusually though, Ley invited two of his colleagues to offer their differing thoughts on the matter. While all three men were in total agreement about the need for a lunar observatory, and its inevitability, they differed on their expectations and concerns regarding it. Astronomer Donald H Menzel argued for a nearside radio telescope which could use occultations by Earth as a tool, for new construction methods to reduce mirror weight, and for electronic detectors (akin to early versions of today’s digital detectors) to avoid vacuum work for astronomers:

“As a matter of fact, electronic receivers would carry the image from the telescope itself to underground, pressured chambers where the observer could operate in comfort. Remote control would enable him to perform all of the necessary telescope operations.” 

He also strongly advocated construction of an UV or X-ray observatory - able to observe frequencies absorbed by Earth’s atmosphere.

Richard S Richardson, also an astronomer and science writer, as well as himself a science fiction author, began his response with a slightly tongue-in-cheek practical consideration:

“There is one aspect to this business of putting an observatory on the Moon that has me worried. What are the astronomers on Luna going to use as a subject for conversation? Astronomers are not the sort of people who have a large fund of small talk. They consist mostly of grim, taciturn individuals with a gloomy outlook on life.”

Richardson suggests that without being able to discuss the seeing (the impact of current atmospheric conditions on image quality) conversations will languish. More seriously, he noted the accessibility of the ultraviolet from the Moon, and that two telescopes sited 180 degrees apart would be essential for full sky coverage. Interestingly, he also noted the impact of the Moon’s precession about its axis (basically its wobble over a 20 year interval) on the stability of sky coordinates used to find stars. While this could now be programmed trivially into a computer, this was not easily possible in the mid-nineteen sixties.

Throughout its history, science fiction has been quick to respond to our changing understanding of the possibilities of the Moon for astronomical observation. The choice of radio telescope versus optical (and now gravitational wave!), nearside versus farside, crewed versus remotely operated, have all been discussed, as have been changes in the technology and materials available.

Apart from the conviction that the construction of such a facility is imminent, and the ever increasing issues of radio noise and light pollution on Earth, little has changed since the 1950s. Proposals for building lunar observatories continue to be made, and feasibility studies published, including several concepts explored by NASA. The farside of the Moon, in particular, is still recognised as a prime location for radio observatories due to its ability to block Earth’s radio noise and the need for very large dishes or arrays (due to the long wavelength of radio waves). For optical telescopes it is perhaps less obviously an advantage to be on the Moon rather than in space, unless a substantial fraction of the construction and manufacture can occur in situ. Indeed, protecting highly polished mirrors from the abrasive lunar regolith (dust), as well as micrometeorites, would be a challenge for many lunar locations. For nearside locations, even the vanishingly thin atmosphere of the Moon might present a limitation, while the limited sky visibility at any one time (relative to a deep space location such as L2) might also be a constraint.

Despite this, it’s worth mentioning that, since it is so hard to get telescopes above the Earth’s atmosphere, even the tiny telescopes that have actually been deployed on the Moon have made substantial contributions. The Far Ultraviolet Camera/Spectrograph, a small telescope just 75mm in diameter, designed by George Carruthers was carried by Apollo 16 and erected on the Moon in 1972, taking a film including 178 images [6].

With advances in technology for both remote operations and imaging, robotic lunar telescopes have also become possible. The Lunar-based Ultraviolet Telescope (LUT) was carried by the Chang’e 3 lunar lander in 2013. At 15cm in diameter, it was twice the size of its predecessor and took extensive data during a mission that lasted far longer than the anticipated one year. The next Chinese mission, Chang’e 4 also carried a telescope, becoming the first to land a radio telescope (albeit a small one) on the lunar farside. Its Low Frequency Radio Spectrometer wasn’t, however the first radio telescope to operate in the Moon’s shadow. Radio Astronomy Explorer B (a.k.a Explorer 49) was a radio telescope mission which operated briefly in orbit of the Moon between 1973 and 1977, never touching down but nonetheless benefitting from the shielding effect of the Earth’s bulk.

Several other telescopes intended for use on the Moon have been constructed, either in part or whole, but been shelved when the lunar probes intended to carry them were cancelled or failed. With the current Artemis programme intended to return America to the Moon, the idea of lunar observatories, crewed or otherwise, is once again current in the scientific community and science meetings have been held at venues such as the Royal Society on the topic in recent years.. While such facilities would typically be expected to operate robotically (as indeed many telescopes on Earth now do), some would benefit from human intervention or supervision during deployment, and all would require launching from sufficiently powerful boosters - far stronger than those used for putting satellites in Earth orbit.

Three low frequency pathfinder experiments are intended for lunar launches in the near future. Both the European Space Agency (ESA) and NASA are actively pursuing studies for more ambitious dishes or interferometers. Indeed ESA has recently tendered for the construction of low frequency antennae as part of its Astrophysical Lunar Observatory (ALO) design studies. NASA’s main focus appears to be on the Lunar Crater Radio Telescope concept being developed with CalTech. Despite short term fluctuations in funding due to political pressures, there now appears to be momentum behind such projects. Chinese scientists are also presenting advanced design studies, such as the Large-scale array for radio astronomy on the farside (LARAF) which can be (and may be) deployed with current launch technology. Effort on (and funding for) UV/Optical/Infrared telescopes is more concentrated on plans for deep space missions - it may yet be sometimes before we see the 100m or even 1km mirrors described in some science fiction, although a number of lunar missions are likely to carry small telescopes as part of their payload and larger facilities are still discussed. A lunar gravitational wave observatory, such as that described by Baxter’s Gauguin’s Questions, is probably still further off, with more stringent requirements and a more challenging construction, but is nonetheless being considered and evaluated by scientists.

We may yet see lunar astronomy beginning to take off during our lifetimes. However, perhaps the most interesting aspect of the science fiction of lunar observatories is the central role of scientific research in general, and astronomy in particular, in our visions of space utilisation. Since before the first astronauts ventured to the Moon, science fiction writers and their readers have had no doubt that the wonder and rigour of scientific discovery would be an integral part of our first settlements on a new world. We can only hope they prove correct.