Building telescopes on the Moon could transform astronomy
theconversation.com
theconversation.com
Astronomers can justify any amount of spending you ask them to, based on whatever incremental learning a telescope of a new type can be built for, based on:
-- size of telescope
-- new sensors
-- background noise reduction, sensitivity
-- frequency domain, spectroscopic resolution
-- it goes on and on
Who provides the external check of whether the latest improvement is worth spending the money? Because astronomers will always say it's worth it on some dimension. How do we decide whether that dimension is worth the money?
Is pushing the discovery of some metal content in an early galaxy by one more unit of redshift worth $10B? Study of dust obscuration of some nebula really pushing the boundaries of our understanding like it was 50 years ago? (or similar esoteric questions)
What $ / unit scientific discovery is worth it?
Edit to add: and yes there are things like the decadal survey and the “industry” has to justify itself to Congress (in the US at least). And yes, I generally do think the finding of this is (at these levels) probably going to bring some net positive multiplier benefit even if hard to quantify. And is more value per money than sending it to war to use an extreme comparison. But I wish there were a more defensible bar for knowing, other than public opinion or “at least we’re not as much a waste as <xyz>”.
Just lucky for astronomy that at least they produce pet pictures for the public to support. But sad for other important fields that don’t have this luxury.
I imagine a lot of space development is similar. The real reason for the huge investment is for defence applications, but it is more acceptable to justify it by the scientific ‘value’ of the projects.
If you asked someone if they wanted $1billion to go to health research or space research the answer would be obvious.
Honestly this depends. If we have 1000 billion going into health research, but 1 billion doing into space research, I think there's an open question on how much good an extra 0.1% of health research will do compared to doubling space research.
In absolute terms instead of relative, I would prefer a billion on most space based research than a billion going to study male pattern baldness.
More so when it's not obvious.
The size and shape of the Hubble is directly influenced by those satellites, and in particular the surprisingly cheap main mirror optics provided you built a mirror of exactly a particular size that it would turn out there was a very experienced and equipped facility in the US for building.
"Secret History of Silicon Valley" https://www.youtube.com/watch?v=ZTC_RxWN_xo
The scientific betting principal could be used to optimally size bets on which research will benefit humanity the most.
My biggest question is why they aren't putting tons of pressure on getting a telescope that can do gravitational lensing to see as far into space as possible ASAP. But again I'm probably just speaking out of turn not being familiar with the wider industry/culture/economics.
You are likely interested in the FOCAL project. https://en.wikipedia.org/wiki/FOCAL_(spacecraft)
> FOCAL (an acronym for Fast Outgoing Cyclopean Astronomical Lens) is a proposed space telescope that would use the Sun as a gravity lens. The gravitational lens effect was first derived by Albert Einstein, and the concept of a mission to the solar gravitational lens was first suggested by professor Von Eshleman, and analyzed further by Italian astronomer Claudio Maccone and others.
> In order to use the Sun as a gravity lens, it would be necessary to send the telescope to a minimum distance of 550 astronomical units away from the Sun, enabling very high signal amplifications: for example, at the 203 GHz wavelength, amplification of 1.3 x 10^15. Maccone suggests that this should be enough to obtain detailed images of the surfaces of extrasolar planets.
---
That 550 AU... for comparison, Voyager 1 is currently at about 159 AU and moving at 3.6 AU/year.
New Horizons is "only" 55.6 AU and going at 2.9 AU/year.
But its an interesting project.
And since its there now...
SPACECRAFT
NAME Voyager 1
RANGE 23.80 billion km
ROUND-TRIP LIGHT TIME 1.84 days
SOURCE VOYAGER 1
FREQUENCY BAND X
DATA RATE 160.0 b/sec
POWER RECEIVED -160 dBm (1.0 x 10-22 kW)Communication protocols at that distance are kind of interesting. Things like dropped data and delays can make it challenging.
https://en.wikipedia.org/wiki/Interplanetary_Internet
https://www.nasa.gov/directorates/heo/scan/engineering/techn...
https://ipnsig.org/tag/deep-space-network/
https://www.nytimes.com/1990/10/02/science/spacecraft-passes...
> A very rare planetary alignment would occur in the late 1970’s allowing a spacecraft to visit all the outer planets (Jupiter, Saturn, Uranus, Neptune and Pluto) using gravity assists at each planet to send it on to the next. This unique alignment would not occur again for another 175 years!
https://pds-ppi.igpp.ucla.edu/archive1/VGLE_1001/DOCUMENT/MI...
> During the late 1970's, alignment of the outer planets affords a variety of multi-planet launch opportunities. From the standpoint of Jupiter flyby distance, the 1977 opportunity (Bourke et al., 1972; Schurmeier, 1974) is the most favorable for reaching Saturn via a gravity-assist swingby of Jupiter. Two advanced spacecraft will be launched during a one-month launch period which opens on August 20, 1977. Each spacecraft will be launched by a Titan IIIE/Centaur D-IT from Launch Complex 41 at the Air Force Eastern Test Range. Final Earth-departure injection velocity will be delivered by a solid rocket portion of each spacecraft. After solid rocket burnout and jettison, the remainder of each spacecraft, having a mass of approximately 825 kg, begins its cruise to Jupiter.
https://commons.erau.edu/cgi/viewcontent.cgi?article=2830&co...
https://solarsystem.nasa.gov/missions/voyager-2/in-depth/
> The two-spacecraft Voyager missions were designed to replace original plans for a “Grand Tour” of the planets that would have used four highly complex spacecraft to explore the five outer planets during the late 1970s.
> In 1974, mission planners proposed a mission in which, if the first Voyager was successful, the second one could be redirected to Uranus and then Neptune using gravity assist maneuvers.
> Although Voyager 2 had fulfilled its primary mission goals with the two planetary encounters, mission planners directed the veteran spacecraft to Uranus—a journey that would take about 4.5 years.
> In fact, its encounter with Jupiter was optimized in part to ensure that future planetary flybys would be possible.
> The Uranus encounter’s geometry was also defined by the possibility of a future encounter with Neptune: Voyager 2 had only 5.5 hours of close study during its flyby.
https://www.scientificamerican.com/article/salvaging-nasas-g...
> When the twin spacecraft were launched, NASA was taking advantage of a rare alignment of Jupiter, Saturn, Uranus and Neptune that occurs once every 175 years to send probes on a "Grand Tour" of the solar system. The alignment allowed the spacecraft to harness the gravity of each planet and swing from one to the next using relatively minimal amounts of fuel. NASA first demonstrated the technique with its Mariner 10 mission to Venus and Mercury from 1973 to 1975.
https://www.secretsofuniverse.in/voyagers-planetary-alignmen...
> ... Why did the engineers at JPL push so hard for this mission to be done? Gary Flandro was the mastermind behind all this, and what he discovered back then in 1964 was groundbreaking. It absolutely changed the game. To be fair, we have to go even further back because as important as Gary Flandro was, he was not the one to lay the foundations for this.
> We’re in 1961, looking at a mathematician named Michael Minovitch. He was a 25 years-old graduate student who decided that he wanted to tackle one of the most interesting and fundamental problems in the history of physics: the three-body problem. It was something Newton himself couldn’t figure out. However, Minovitch had a powerful tool that Newton didn’t have, and that was an IBM computer. He was so excited about the new IBM computer at UCLA that he felt like giving a shot at this.
http://www.gravityassist.com/IAF3-2/Ref.%203-148.pdf
... and then probably the most important paper in all of this: Utilization of Energy Derived from the Gravitational Field of Jupiter for Reducing Flight Time to the Outer Solar System http://www.gravityassist.com/IAF2/Ref.%202-123.pdf published in 1966.
> 4. Conclusions
> The 1975-1980 time period is characterized by an abundance of interesting multiple planet trajectories which efficiently utilize energy derived from a close approach to the planet Jupiter. The trajectories discussed here are characterized by very short flight times in comparison to those for direct flights from Earth to the corresponding target planets. Although higher launch energies are suggested for some of the multiple planet flights, the additional expense of this energy might be offset by the great savings afforded by the short flight times. This is due to the expense of providing adequate vehicle reliability for the extended flight duration characteristic of direct trajectories and to the high costs involved in maintaining tracking, orbit determination, and other flight related activities for protracted periods.
---
... And so, the Voyager probes became some very fast moving probes.
Note that the Voyager probes are 825 kg... while New Horizons was 478 kg at launch time.
You can go faster for getting to 550 AU... with a less massive probe. That's why New Horizons is as fast as it is. For that 3.6 AU/y rate - we haven't launched anything that will overtake them yet. That's going 1/3 the way from Earth to Saturn "direct" each year... twice as fast as Cassini took to get to Saturn. ESA just launched JUICE... it's going to to take 8 years to get to Jupiter (5.2 AU). The current speed of Voyager could do it in a year and a half... but that's with all the gravity assists that it got to where it is now.
Even more reasons to be an evangelist for this sort of project. Compared to settling Mars this seems infinitely more important unless you have some hyper skeptical view of human society. Seeing the surface of extrasolar planets should be the #1 goal easily IMO
Planet. Singular. Not plural. The nature of gravitational lensing is that you would need to build and place a new telescope for every different direction you want to look. The relevant quote from the linked wikipedia page is: “FOCAL would be able to observe only objects that are right behind the Sun from its point of view, which means that for every observed object a new telescope would have to be made.”
> Compared to settling Mars this seems infinitely more important unless you have some hyper skeptical view of human society.
My “hyper skeptical” view of human society is that it is fragile. There are many possible catastrophes which could wipe all of us out, then there are many other possible situations which would not kill all of us but would shunt humanity forever. Settling Mars would make us more resilient in two major ways: The settlement on Mars is a physical off-site backup to human society. And the necessary R&D to achieve a self-sustaining Mars setlement would force us to develop and test for reliability under real world circumstances tech which we could use here on Earth to better survive many of those calamities. It is literally a ticket to raise the probability of the continued existence of humankind.
On the other hand a picture of an exoplanet is a picture. An interesting one sure. If we would have it now it would be probably front page news. It would be a blurry pixelated disk with smears of colour. That would be all for 99% of humanity. For the select few they would study the image and analyse it and we would have follow on studies in a few years saying things like: “We are reasonably sure this area is a shallow sea, and we think this colour fluctuation is consistent with an algea bloom.” Iff(!) we got lucky and the exoplanet we aimed the telescope at is not a dead, dry rock.
So increasing the chance of our survival vs a blury picture which will pose more question than it answers. How are these two goals in any way comparable? Let alone the second being more important?
I guess I have more hope for the species in the near term and getting those photos seems to be something I personally care more about. But the two things are different you're right.
I don't think that a bolide crashing into our planet and flash-boiling the oceans will care about our hope. Not every danger we are facing is anthropogenic sadly. Some things are just up for luck and happenstance.
I am on the "this is a really hard problem - but an interesting one" category. It seems like it will take a number of significant improvements on top of current technology - but it seems like it would be doable in another few decades if we continue to improve (the difference between Pioneer and New Horizons is 35 years... if we can do that much improvement again we might have something).
It is still something that if you are a grad student working on it now, it would launch when you retire, and your grad students when you retire - when they retire, it is their grad students who would be doing analysis of the data.
I tend to believe this would be a good thing to do because it would be working on that time frame and getting us to think about projects that will run for a century rather than a budget cycle.
Thank you. I'm familiar with the general arrangement, but haven't read that one yet.
> I am on the "this is a really hard problem - but an interesting one" category.
Absolutely! I'm fascinated by these proposals. So much so that I wanted to write a simulator to study the control challenges of a project like this.
> I tend to believe this would be a good thing to do
I'm with you on that. I just don't think it has the same utility as an off-planet settlement. Luckily, I believe we can and should do both.
Regardless, poverty isn't mainly a problem of wealth scarcity, but instead of wealth distribution. So even if you stopped spending on any research that doesn't have a short-term justification, I don't think that money would end up alleviating poverty, but instead going to fund somebody's slightly bigger superyacht.
Instead I get flipping news about stupid Kardashians or some navel gazing shit like wars, stupid ideologies, etc. etc. all day, every day.
A very similar argument can be made for particle physics and their colliders. Yes, telescopes produce pretty pictures, but fundamental particle physics occasionally produces practical results.
Well, they used to (the colliders I mean). Modern particle physics seems to be more in the confirmation stage of current theory rather than a discovery phase like it used to be maybe 40 years ago.
Meanwhile astronomy keeps opening up new questions about the universe that require even better equipment to attempt to answer.
Building better colliders and better telescopes are interesting end goals, but also consider what goes along with them.
Building them means funding multiple generations of new theorists and engineers. A lot of those people do fundamental research and then branch out to both found new commercial companies based on those discoveries and to work for those companies.
I think it's better to look at "big science" in a much broader perspective. The new collider or telescope might "cost" $10 billion, but that isn't the cost of building the machine and its materials.
Most of that money goes into paying people across a very diverse field of professions to do the research and engineering required to make that big pretty picture machine work. That's the stuff that drives technical innovations at the edge of what we apes currently understand.
When we fall back to asking why build pyramids, cathedrals, highways, rockets, or anything else that requires a vast number of people to work towards the same goal, don't forget about what everyone gets from the journey on the way.
There's a ton of surface treatment in materials science that amounts to firing a beam of atoms at a surface and/or bathing it in a plasma in order to get a unique chemical structure.
The problem is to deduct second order laws and rules behind the observed bits and screws flying. Car factories, assembly lines and cnc machines..
By use of horrible metaphors, we summone the oh might particle physicists into the cycle of cyclotron..
PS: Material science wouldnt know what it would get away with outside of try and error - without particle physics..
Now there isn't a clean 2-step line if-boson-then-gorilla, but knowledge spreads and fills the gaps otherwise filled with just question marks.
The James Webb telescope cost 10 billion, but that was spent over 17 years, and it should work for 20 years or so.
Compared to the budget as a whole, it is insignificant.
And the pretty pictures do serve a wider purpose. They will be part of the space inspiration for the next generation. Out there are kids dreaming of space, and the opportunities there etc.
Who knows, maybe the first asteroid miner is already with us, inspired by some James Webb picture on his bedroom wall.
But compared to the government’s science funding through the NSF, it is an order of magnitude larger than entire major fields of academia!
> Compared to the budget as a whole, it is insignificant.
No. A lot of the cost of the JWST was driven by the limitations of the launch vehicle. Engineers needed to come up with the very complex folding and unfolding mechanism, and that was for a thing produced in a quantity of 1.
Once the SpaceX Starship gets going, these limitations disappear. All of a sudden. I predict that by the end of this decade there will be numerous telescopes in the sky with capabilities surpassing JWST's, and built and launched for dirt cheap compared to JWST.
One problem with science is and will always be this: things that cost $10 billion now might very well cost $100 million in 2 decades.
The question that nobody asks when funding mega scientific projects is not what is the bang for the buck, but is it worth to pay big bucks for a given bang now, or can we wait 2 decades and get the same bang for 100 times less money?
>Well, they used to (the colliders I mean). Modern particle physics seems to be more in the confirmation stage of current theory rather than a discovery phase like it used to be maybe 40 years ago.
There are some good arguments as to why a muon collider might be a really good thing to build, and why it would be smaller than the LHC. CERN already has a program to look into it.
If you have an hour this is a good talk by Nima Arkani-Hamed about muon colliders from last month. https://www.youtube.com/watch?v=wKPwzezceGo&t=3379s
But to address your point about being in the confirmation phase, you can go to this particular time stamp, where he talks about why a muon collider is a good way to probe the higgs boson itself, which is new science.
Everyone has a story on how they will provide value, and the funders must decide who offers the best ROI.
The Decadal Survey does not determine the overall level of funding for astronomy. It just says, "If you gave us X amount of money, here's how we would divide it up, based on what we think are the most important questions in our field." There's a competitive process within the community to propose projects and argue for different scientific research areas, which eventually gets distilled down into a set of funding recommendations.
The Decadal Survey is really just a recommendation to the funding agencies, which can ignore it if they wish. However, since it does represent the consensus of American astronomers, it's taken very seriously.
As for the overall level of astronomy funding, astronomers have very little control over that. That's decided at a political level, by Congress, and I doubt there's any rigorous cost-benefit analysis to society going on there.
0. https://www.nationalacademies.org/our-work/decadal-survey-on...
1. Basic research directly underpins the vast majority of the technology we have available. Or at the minimum provides the framework with which we understand how technology operates, making it easier to improve. I think the utility of this is greatly underappreciated.
2. It's impossible to know in advance how useful some basic piece of research will prove to be in the future. We can only guess at the $ value, and many of the most useful results are surprises from blue-sky research not applied goal-orientated work.
3. Academia produces an army of highly-trained disgruntled postdocs and PhD students (just look at the ratio of student to professor positions) who have beneficial transferable skills for industry. It's not that you can't learn to do research outside of the academic environment, but getting a PhD is good training for it.
Finally, just guessing here, but did you work on galaxies or the ISM? We're on the cusp (a couple of decades) from imaging potentially habitable Earth analogs with next-generation space missions. This is a huge step toward answering the 'are we alone' question. Personally, I'd happily spend a few billion on that though I know not everyone would agree...
Would love to hear more!
There are currently three ways of studying exoplanets: the transit method, the radial velocity method and direct-imaging. (I'm excluding gravitational microlensing which is a fantastic technique for studying populations of planets, but each lensing event is a one off so the exoplanet is not amenable to follow-up observations.) The radial velocity method works by very carefully measuring the movement of a star (can reach sensitivities as low as a few meters per second!) in response to the planets orbiting around it. This gives us a good mass estimate, but no way to know about the atmosphere of the planets to search for biosignatures.
The transit methods works on chance alignment; occasionally a planet will cross ('transit') its host star blocking out a portion of the light that would otherwise reach us (~1% for Jupiter, ~0.1% Neptune, ~0.01% Earth). We're able to detect this dip/shadow and infer the presence of the planet indirectly. Some of the light from the star will filter through the planets atmosphere and we can use this signal to infer the composition. However, there are some limitations. Earth's radius is 6,400km and the atmosphere is about 100km in height, or about ~0.15% of the radius. If the signal from an Earth like planet in transit is about ~0.01% you can imagine how much smaller the signal from the atmosphere is. So in practice, when doing 'transmission spectroscopy' you want to observe multiple transits and combine them together to boost the signal. This works well for planets on short orbits, but if one orbit takes a year then we have to wait a long time search for our aliens...
Direct-imaging on the other hand aims to have a spatially separated image of the planet orbiting its host star. The planet itself isn't resolved - it's just a point of light - but it's separate from the star and so we can directly study its atmosphere. The technical challenges with imaging are extremely difficult, and primarily stem from the fact that the planet will be incredibly faint (~10^-10 times) compared to the host star. For comparison this is much smaller than aberrations induced by minuscule nanometer imperfections in your mirror, or by temperature induced changes in your optics. But, to make it feasible, we can use a coronagraph to block out most of the light of the star, observing from space affords a very stable temperature environment and use post-processing of the images to further boost sensitivity.
Finally this leads us to the next generation direct imaging missions. Three key examples are LIFE, HabEx and LUVOIR. All three are in the concept phase, but the key idea is to have a large mirror in space (4m for Habex and 8m or 15m for LUVOIR). One big enough to comfortably spot an object as faint as an Earth sized planet in reflected light from it's host star. The trick with HabEx is that they also want to use a starshade flying in formation with the telescope to physically block out light from the star being observed. A starshade would theoretically be much better at blocking out light than our current coronagraphs. LUVOIR is just plain big. Finally, LIFE is a little different. Instead of one large mirror it is a mission that relies on interferometry to search for biosignatures. By combining light from several different telescopes flying in tight formation you can simulate a much larger mirror and achieve a similar effect.
I'm leaving out a lot of details but I hope this gives you an idea of the direction astronomers are taking. Someone else mentioned the decadal survey (Astro2020), this is a great place to read some of the technical details. Feel free to PM any questions. It's not clear which one of these missions will be successful, and needless to say the required technology development is huge. However, I strongly suspect we'll be able to say something about habitability of a few dozen Earth like planets in the next couple of decades which is an incredible prospect. If we're lucky maybe we'll even see a biosignature!
I'm surprised you don't know that as someone from the field.
On the general level, it is the elected politicians that decide of the budget of the state, and which part goes to science and to which science branch. On the specific level, it's the science organizations (usually staffed by scientists) that decide who get what based on the quality of scientific proposals.
Scientists don't get money just because. They have to write lengthy proposals justifying their requests. These proposals are examined by other scientists and compared to others, and the most promising are awarded money. It can take decades to go from an idea to having a project funded.
Also there is no "unit scientific discovery" so no $/unit scientific discovery can be evaluated
I do hope we try it though, speaking from my inner 12 year old.
https://science.nasa.gov/science-news/science-at-nasa/2006/1...
It would be pretty sweet to have a decent scope on the far side of the moon.
I don't know if this will affect moon based telescopes in a way that can't be mitigated tough.
Quote from "Moon Storms" [1]:
"To everyone's surprise," says Olhoeft, "LEAM saw a large number of particles every morning, mostly coming from the east or west--rather than above or below--and mostly slower than speeds expected for lunar ejecta." What could cause this? Stubbs has an idea: "The dayside of the moon is positively charged; the nightside is negatively charged." At the interface between night and day, he explains, "electrostatically charged dust would be pushed across the terminator sideways," by horizontal electric fields.
[0] "Moon Fountains" https://web.archive.org/web/20100319112529/http://science.na...
[1] "Moon Storms" https://web.archive.org/web/20100106144102/http://science.na...
That's entirely orthogonal to whether the wind storms eventually clear dust from the panels.
The linked article makes it pretty clear that the opposite is true; eventually the panels are completely obscured by dust, not cleared.
Actually you can probably get the same outcome by putting land optical scope astro people up against space optical or RF people. "all that launch cost spent on active optics here on the ground could.."
To give you an example, using adaptive optics, you can get higher resolution on small fields of view from the ground. That's because you can build much larger telescopes on the ground, which therefore have a smaller diffraction limit, and you can use adaptive optics to correct for the atmosphere in a small field of view. However, if you want high resolution over a large field of view, you have to go to space.
Other advantages of space: extremely stable calibration (because you can control conditions more precisely, and because there's no atmosphere) and ability to view parts of the spectrum that are unavailable from the ground.
Other advantages of ground-based telescopes: larger and heavier instruments, ability to do repairs and upgrades.
Robots vs. manned spaceflight is much simpler. Robots will almost always give you more science return for the same price. I still think manned spaceflight should be pursued, but for other reasons (it's cool, and we should be pushing the envelope of what's possible).
> The lunar far side is permanently shielded from the radio signals generated by humans on Earth. During the lunar night, it is also protected from the Sun. These characteristics make it probably the most “radio-quiet” location in the whole solar system as no other planet or moon has a side that permanently faces away from the Earth. It is therefore ideally suited for radio astronomy.
Maybe we need to treat this as a "pristine natural resource" and put some treaties in place now where we agree to limit how much we "pollute" this area with RF signals, before it's too late?
There is no 'dark side of the moon'. During a new moon the dark side is the front side. At a full moon it's the back side. You probably don't want to be doing optical astronomy during the middle of the day on the moon, and you probably don't want to be doing radio astronomy while being pelted by the solar wind. Much of both is taken care of if you're doing it near midnight on the lunar day.
I'm surprised this proposal hasn't been tried sooner. Is this because the cost per pound to send something into space has gotten cheaper? Why now?
I think we will be okay.
I know the media likes to hyper-focus on SpaceX, but it should be noted that Starlink is one of the best large constellations in this regard. SpaceX goes far above and beyond the (inadequate IMO) legal requirements for radio/IR/visible emanations, at substantial engineering expense to themselves.
https://youtu.be/MNc5yCYth5E?t=1717
https://cps.iau.org/news/nsf-and-spacex-sign-agreement-to-mi...
If you really want to get mad about badly-designed satellites impacting astronomy, look up AST SpaceMobile.
Note that the two aren't mutually exclusive: Artemis 3 uses [1] Starship as a major component, and it's likely that Starship will take over other parts of the works for the reason you note.
No doubt some physicists of the future are going to be very interested in the contents of those lenses. Kind of the "pitch drop experiment" of astrophysics, I suppose.
[1] - https://www.hasselblad.com/about/history/hasselblad-in-space...
The unanswered question is if this is blocked out from earth communication, what are you doing for earth communication? Moon satellites? Optical relays? Would it go to the Mars satellites? These things get booked so far ahead of time, you can probably pretty easily schedule the dark times when it couldn't talk to Mars especially if you send it up with modern storage tech.
I guess there's also Venus satellites coming around soon as well.
Actually I think this is already being planned anyway, unrelated to a telescope.
https://www.nasa.gov/feature/does-anything-orbit-the-moon-we...
It all can be done but takes propellant.
So that implies that in the Apollo missions, the command module had to burn fuel to stay in orbit around the moon? And I guess if anything had delayed the landing module from its scheduled return, the command module might have run out of fuel and been forced to abandon the astronauts on the moon?
It is possible to build a refracting telescope in space that uses earths atmosphere as a lens. This is far more practical (ie smaller) than any gravity telescope.
https://www.science20.com/tommaso_dorigo/the_terrascope_usin...
In short, it's far easier and more effective to use the Sun for this effect. Radio interferometry would be a better use for Moon-based observatories, if we felt like building several of them.
Edit: I forgot the moon has a much lower gravity than Earth. It might still be worthwhile to build in orbit, but we can build a lot bigger on the moon than on Earth.
> Gravitational anomalies slightly distorting the orbits of some Lunar Orbiters led to the discovery of mass concentrations (dubbed mascons) beneath the lunar surface caused by large impacting bodies at some remote time in the past. These anomalies are of sufficient magnitude to cause a lunar orbit to change significantly over the course of several days. They can cause a plumb bob to hang about a third of a degree off vertical, pointing toward the mascon, and increase the force of gravity by one-half percent.
> ...
> Study of the mascons' effect on lunar spacecraft led to the discovery in 2001 of "frozen orbits" occurring at four orbital inclinations: 27°, 50°, 76°, and 86°, in which a spacecraft can stay in a low orbit indefinitely.
Consider that - there are only four inclinations where you an orbit the moon without needing to do constant adjustments. Whereas with the Earth basically all the inclinations are available.
https://en.wikipedia.org/wiki/Frozen_orbit and https://science.nasa.gov/science-news/science-at-nasa/2006/0... for more on this.
Arecibo was 73,000 square meters while JWST is "only" 25 square meters.
For this, building it in a crater on the moon and allowing the moon itself to help support it is advantageous.
... and has some interesting scaling up possible.
https://www.researchgate.net/publication/258694444_Implement...
Dark energy is the odd one that is part observation, part speculation
Given the above, why is there so much postulated "dark matter"?
Could one theoretically point the hubble at the james webb mirrors and see anything?
The JWST is about a million miles away from earth. It is only 6.5 meters wide.
tan = 6.5 meters / 1M miles = 4.03891275 × 10-9
2.31×10^-7 degrees
2.78×10^-5 degrees
Why is HN taking after reddit so much lately with duplicates?
I believe GP was being facetious for the sake of levity.
E.g. sometimes vast internal 'oceans' are somehow implied by water vapor escaping from the surface of a moon. For the sake of visiting astronauts, I hope some of this 'water' turns out to be real.
(Wherever the water in the Earth's oceans really came from is at least, finally, being questioned.)
Why is water in scare-quotes? Is the implication that it is something other than water?
Is there a supposed meaning behind this tendency to look for water in places? I assume any sufficiently large celestial body gets a bit of eyeball time, and the ones that have water are bumped into the “interesting” bin because if we hypothetically ever hope to go there, that’s one necessary thing for survival off the list.
What is the last parenthetical about? The water on Earth was at some point in space, after all, there’s no alternative…