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The possibility of building a telescope on the moon has long seduced many people. But, with one exception, it is a terrible idea that is much worse than being at the bottom of interplanetary space.NASA / Lunar and Planetary Institute
If you want to take the most original and unpolluted images of the universe, your best bet is to leave the Earth behind you. Here on our planet, there are all kinds of effects that interfere with our imaging capabilities. Light pollution limits the depth of vision. the atmosphere hinders our resolution power and our ability to observe clearly; clouds and weather interfere with our light collection goals; the sun and the earth itself prevent us from seeing large parts of the sky from all the terrestrial places.
Yet observatories such as Hubble, Chandra, Fermi, Spitzer and others have shown the remarkable efficiency of a space telescope. The views and the data they sent back to Earth taught us more than any similar observatory could have revealed of the Earth. So why not install a telescope on the moon? Believe it or not, it's a terrible idea in every respect except one. Here's why.
The transmittance or opacity of the electromagnetic spectrum through the atmosphere. Write down all the absorption functions in gamma rays, X-rays and infrared. That's why they are better seen from space. On many wavelengths, like on the radio, the floor is just as good, while others are simply impossible.NASA
The Moon, at first glance, seems to be the ideal location for a telescope. There is virtually no atmosphere, eliminating all light pollution problems. This is far from the Earth, which should greatly reduce the interference of any signal produced by humans. The very long nights allow you to observe the same target, continuously, up to 14 days at a time, without interruption. And as you have a solid ground to prepare yourself, you do not need to resort to gyroscopes or reaction wheels to steer you. It looks like a very good deal.
But if you start thinking about how the moon orbits around the Earth, with the entire Earth-Earth system orbiting the Sun, you might begin to understand some of the problems that such a configuration would inevitably encounter.
It takes a little more than 27 days for the Moon to perform a 360 ° orbit around the Earth, but still a little over 29 days to go from new moon to new, but a total of 14 lunar cycles, or 411 days , to move from a full Moon of Perigee to a Perigee Moon again because of the movement of its elliptical orbit around the Sun. The Earth-Moon-Sun configuration is essential to understand the implications of building a lunar observatory.User of Wikimedia Commons Orion 8
First, if you place your telescope on the moon, which side do you choose: the near side or the far side? One or the other has drawbacks.
If you place your telescope on the near side (facing the Earth) of the Moon, you will always have a view of the Earth. This means that you can send and receive signals, control your telescope and download / download data in near real time, only the time of travel of light signals in the space limiting you. But it also means that interference from the Earth, such as radio signals, will always be a problem against which you must protect yourself.
On the other hand, if you are on the other side of the moon, you protect yourself fairly effectively from everything that comes from the Earth, but you also do not have a direct path to it. data transfer or signal transmission. An additional mechanism should be put in place, such as a lunar orbiter or a link to a near-side transmitter / receiver, just to make it work.
The near and far sides of the Moon, restored with the help of images from NASA's Clementine mission.NASA / Clementine Mission / Lunar & Planetary Institute / USRA
Whatever it is, you will have to deal with a host of problems that you would not encounter simply by going into the solitary abysses of interplanetary space. The two biggest ones are:
- Moonquakes. Do you think the moon is a big problem because it's responsible for the tides of the Earth? The tidal forces exerted by the Earth on the Moon are more than 20 times greater than the tidal forces of the Moon on Earth, enough for the Moon to undergo significant moonquakes.
- Extreme temperatures. Due to the tidal lock on the Earth and its extremely slow rotation, the Moon is bathed in constant light for 14 days, followed by 14 days of total darkness. Daytime temperatures can reach more than 200 ° F (near 100 ° C), while the night reduces the cold to -280 ° F (-173 ° C).
The Earth, as seen, rises on the lunar branch at a point where the Sun is barely falling on the surface of the Moon. You can say that it's a photo of the lunar face, otherwise the Earth would not be visible at all.Japan Aerospace Exploration Agency, JAXA / NHK, Kaguya (Selene)
While a space telescope can control its temperature through active or passive cooling (or a combination of both), a telescope must cool below the temperature of the wavelengths that it tries to # 39; observe, otherwise the noise will invade your signal. This would be a huge disadvantage for astronomy in the ultraviolet, optics or infrared, all of which would have serious problems on the moon for something other than the purpose of the sun. observation of the Earth (or the Sun).
Designing a telescope capable of surviving these extreme temperatures while operating optimally is a major challenge. It is therefore no wonder that the only lunar telescope we have at the moment is a UV telescope located on the near side of the Moon, at wavelengths where the atmosphere Earth absorbs almost all the light.
The concept of the LUVOIR space telescope would place it at the L2 Lagrange point, where a 15.1-meter primary mirror would unveil and begin to observe the Universe, bringing us untold scientific and astronomical riches. Note the plan to protect yourself from the sun to better isolate it from a broad spectrum of electromagnetic signals. This is far superior to the use of the Moon as a base.NASA / LUVOIR concept team; Serge Brunier (background)
For most applications, going into space will be a better option than going to the moon. The lunar surface, in terms of extreme temperatures and communication difficulties with the Earth, has more disadvantages than having a surface on which to support to support offers.
But there is a very specific application for which the Moon offers an unprecedented advantage over any other environment: radio telescopes. The Earth is an incredibly "radio-strong" source, due to natural and anthropogenic causes. Even in space, the signals emanating from the Earth are ubiquitous throughout the solar system. But the Moon offers a breathtaking environment of immunity to the Earth's radio signals: the far-off portion literally uses the Moon itself as a shield.
A small section of the Karl Jansky Very Large Array, one of the largest and most powerful radio telescope networks in the world. The hidden face of the Moon would be even more isolated, but much more expensive.John Fowler
As cosmologist Joe Silk wrote earlier this year:
The dark side of the moon is the best place in the internal solar system to monitor low-frequency radio waves – the only way to detect some weak "fingerprints" left by the Big Bang on the cosmos. Terrestrial radio telescopes are overly interfered with by electromagnetic pollution caused by human activities, such as maritime communications and short-wave broadcasting, to obtain a clear signal, and the terrestrial ionosphere prevents longer wavelengths to reach these telescopes.
We were able to detect inflationary signals, the beginnings of the Big Bang and the formation of the very first stars of the universe with a lunar radio telescope. Even if we hope to be able to do it, whether on Earth or in space, the hidden side of the Moon offers more sensitivity because it is protected from the Earth, compared to any other option.
While many signals in the CMB and in the large-scale structure of the Universe have verified and validated inflation, the mode B polarization predicted by the tensor modes of inflation has not appeared. This does not mean that inflation is wrong, but rather that models that produce only the largest tensor fluctuations of amplitude are at a disadvantage. A network of radio telescopes located on the other side of the moon could probe signals that even space observatories such as Planck can not find.Kamionkowski and Kovetz, ARAA (2016), via http://lanl.arxiv.org/abs/1510.06042
At present, whenever a spacecraft moves behind the moon, from the Earth's point of view, it causes what we call a radio power outage. The fact that radio waves can not cross the Moon means that no signal can be sent or received during this period. Orbiting satellites, remote or mobile stations, and even Apollo astronauts have no way of communicating with the Earth with the moon.
But that also means that they've been protected from all kinds of radio-contaminant signals occurring on the Earth. GPS communications, microwave ovens, radar, mobile phone and WiFi signals, and even digital cameras, are among the many terrestrial sources that contaminate radio observatories. But on the other side of the moon, all sources of interference from humanity are 100% blocked. It is the most pristine environment we can ask for radio astronomy.
In the absence of atmosphere, visible views of the Earth and even Venus, the night on the other side of the moon is darker than any night on Earth.Jay Tanner
As Dr. Jillian Scudder has already pointed out, there are also disadvantages. Data transmission requires something like an orbiter that can connect to both the Earth and the telescope. A telescope or a set of radio telescopes must be built and deployed on the moon, and linked together if we take the network route. (Which is greatly preferred.) Otherwise, the cables could be routed to the near side for transmission to Earth.
But perhaps the biggest prohibitive element is cost. Moving equipment to the moon, landing on the lunar surface, deploying it, and more is a formidable undertaking. Even the most modest proposal, a Lunar Array for Radio Cosmology (LARC), consists of over a hundred simple design antennas spread over a distance of two kilometers. That would cost more than a billion dollars, just for that, comparable to the most expensive radio stations ever built on Earth.
This shows a particular antenna design that LUNAR is studying. The black X's on the antenna arms are the photon collecting dipoles. The yellow arm is made of a very thin kapton film. The dipoles are connected by an electrical transmission line to the central concentrator, indicated in purple. This hub transmits the data to the Earth.NASA / Lunar University Network for Astrophysical Research / UC Boulder
For almost every conceivable application in astronomy, going to the moon is a place much inferior to the mere superiority of the earth's atmosphere. The extreme temperatures encountered everywhere on the Moon represent an extraordinary challenge beyond any advantage you take from the surface of the Moon. It is only in radio frequencies that the benefits of being on the lunar side provide an opportunity to observe that we can not obtain terrestrial or spatial observations.
Until the costs are reduced or we show that we are ready to pay, it is unlikely that we will see a lunar telescope superior to the other options. The Universe is there, waiting for us to discover its secrets. When we decide that a lunar radio network is worth it, we will go a long way in discovering our cosmic origins.
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The possibility of building a telescope on the moon has long seduced many people. But, with one exception, it is a terrible idea that is much worse than being at the bottom of interplanetary space.NASA / Lunar and Planetary Institute
If you want to take the most original and unpolluted images of the universe, your best bet is to leave the Earth behind you. Here on our planet, there are all kinds of effects that interfere with our imaging capabilities. Light pollution limits the depth of vision. the atmosphere hinders our resolution power and our ability to observe clearly; clouds and weather interfere with our light collection goals; the sun and the earth itself prevent us from seeing large parts of the sky from all the terrestrial places.
Yet observatories such as Hubble, Chandra, Fermi, Spitzer and others have shown the remarkable efficiency of a space telescope. The views and the data they sent back to Earth taught us more than any similar observatory could have revealed of the Earth. So why not install a telescope on the moon? Believe it or not, it's a terrible idea in every respect except one. Here's why.
The transmittance or opacity of the electromagnetic spectrum through the atmosphere. Write down all the absorption functions in gamma rays, X-rays and infrared. That's why they are better seen from space. On many wavelengths, like on the radio, the floor is just as good, while others are simply impossible.NASA
The Moon, at first glance, seems to be the ideal location for a telescope. There is virtually no atmosphere, eliminating all light pollution problems. It is far from the Earth, which should significantly reduce the interference caused by the signals produced by humans. The very long nights allow you to observe the same target, continuously, up to 14 days at a time, without interruption. And as you have a solid ground to prepare yourself, you do not need to resort to gyroscopes or reaction wheels to steer you. It looks like a very good deal.
But if you start thinking about how the moon orbits around the Earth, with the entire Earth-Earth system orbiting the Sun, you might begin to understand some of the problems that such a configuration would inevitably encounter.
It takes a little more than 27 days for the Moon to perform a 360 ° orbit around the Earth, but still a little over 29 days to go from new moon to new, but a total of 14 lunar cycles, or 411 days , to move from a full Moon of Perigee to a Perigee Moon again because of the movement of its elliptical orbit around the Sun. The Earth-Moon-Sun configuration is essential to understand the implications of building a lunar observatory.User of Wikimedia Commons Orion 8
First, if you place your telescope on the moon, which side do you choose: the near side or the far side? One or the other has drawbacks.
If you place your telescope on the near side (facing the Earth) of the Moon, you will always have a view of the Earth. This means that you can send and receive signals, control your telescope and download / download data in near real time, only the time of travel of light signals in the space limiting you. But it also means that interference from the Earth, such as radio signals, will always be a problem against which you must protect yourself.
On the other hand, if you are on the other side of the moon, you protect yourself fairly effectively from everything that comes from the Earth, but you also do not have a direct path to it. data transfer or signal transmission. An additional mechanism should be put in place, such as a lunar orbiter or a link to a near-side transmitter / receiver, just to make it work.
The near and far sides of the Moon, restored with the help of images from NASA's Clementine mission.NASA / Clementine Mission / Lunar & Planetary Institute / USRA
Whatever it is, you will have to deal with a host of problems that you would not encounter simply by going into the solitary abysses of interplanetary space. The two biggest ones are:
- Moonquakes. Do you think the moon is a big problem because it's responsible for the tides of the Earth? The tidal forces exerted by the Earth on the Moon are more than 20 times greater than the tidal forces of the Moon on Earth, enough for the Moon to undergo significant moonquakes.
- Extreme temperatures. Due to the tidal lock on the Earth and its extremely slow rotation, the Moon is bathed in constant light for 14 days, followed by 14 days of total darkness. Daytime temperatures can reach more than 200 ° F (near 100 ° C), while the night reduces the cold to -280 ° F (-173 ° C).
The Earth, as seen, rises on the lunar branch at a point where the Sun is barely falling on the surface of the Moon. You can say that it's a photo of the lunar face, otherwise the Earth would not be visible at all.Japan Aerospace Exploration Agency, JAXA / NHK, Kaguya (Selene)
While a space telescope can control its temperature through active or passive cooling (or a combination of both), a telescope must cool below the temperature of the wavelengths that it tries to # 39; observe, otherwise the noise will invade your signal. This would be a huge disadvantage for astronomy in the ultraviolet, optics or infrared, all of which would have serious problems on the moon for something other than the purpose of the sun. observation of the Earth (or the Sun).
Designing a telescope capable of surviving these extreme temperatures while operating optimally is a major challenge. It is therefore no wonder that the only lunar telescope we have at the moment is a UV telescope located on the near side of the Moon, at wavelengths where the atmosphere Earth absorbs almost all the light.
The concept of the LUVOIR space telescope would place it at the L2 Lagrange point, where a 15.1-meter primary mirror would unveil and begin to observe the Universe, bringing us untold scientific and astronomical riches. Note the plan to protect yourself from the sun to better isolate it from a broad spectrum of electromagnetic signals. This is far superior to the use of the Moon as a base.NASA / LUVOIR concept team; Serge Brunier (background)
For most applications, going into space will be a better option than going to the moon. The lunar surface, in terms of extreme temperatures and communication difficulties with the Earth, has more disadvantages than having a surface on which to support to support offers.
But there is a very specific application for which the Moon offers an unprecedented advantage over any other environment: radio telescopes. The Earth is an incredibly "radio-strong" source, due to natural and anthropogenic causes. Even in space, the signals emanating from the Earth are ubiquitous throughout the solar system. But the Moon offers a breathtaking environment of immunity to the Earth's radio signals: the far-off portion literally uses the Moon itself as a shield.
A small section of the Karl Jansky Very Large Array, one of the largest and most powerful radio telescope networks in the world. The hidden face of the Moon would be even more isolated, but much more expensive.John Fowler
As cosmologist Joe Silk wrote earlier this year:
The dark side of the moon is the best place in the internal solar system to monitor low-frequency radio waves – the only way to detect some weak "fingerprints" left by the Big Bang on the cosmos. Terrestrial radio telescopes are overly interfered with by electromagnetic pollution caused by human activities, such as maritime communications and short-wave broadcasting, to obtain a clear signal, and the terrestrial ionosphere prevents longer wavelengths to reach these telescopes.
We were able to detect inflationary signals, the beginnings of the Big Bang and the formation of the very first stars of the universe with a lunar radio telescope. Even if we hope to be able to do it, whether on Earth or in space, the hidden side of the Moon offers more sensitivity because it is protected from the Earth, compared to any other option.
While many signals in the CMB and in the large-scale structure of the Universe have verified and validated inflation, the mode B polarization predicted by the tensor modes of inflation has not appeared. This does not mean that inflation is wrong, but rather that models that produce only the largest tensor fluctuations of amplitude are at a disadvantage. A network of radio telescopes located on the other side of the moon could probe signals that even space observatories such as Planck can not find.Kamionkowski and Kovetz, ARAA (2016), via http://lanl.arxiv.org/abs/1510.06042
At present, whenever a spacecraft moves behind the moon, from the Earth's point of view, it causes what we call a radio power outage. The fact that radio waves can not cross the Moon means that no signal can be sent or received during this period. Orbiting satellites, remote or mobile stations, and even Apollo astronauts have no way of communicating with the Earth with the moon.
But that also means that they've been protected from all kinds of radio-contaminant signals occurring on the Earth. GPS communications, microwave ovens, radar, mobile phone and WiFi signals, and even digital cameras, are among the many terrestrial sources that contaminate radio observatories. But on the other side of the moon, all sources of interference from humanity are 100% blocked. It is the most pristine environment we can ask for radio astronomy.
In the absence of atmosphere, visible views of the Earth and even Venus, the night on the other side of the moon is darker than any night on Earth.Jay Tanner
As Dr. Jillian Scudder has already pointed out, there are also disadvantages. Data transmission requires something like an orbiter that can connect to both the Earth and the telescope. A telescope or a set of radio telescopes must be built and deployed on the moon, and linked together if we take the network route. (Which is greatly preferred.) Otherwise, the cables could be routed to the near side for transmission to Earth.
But perhaps the biggest prohibitive element is cost. Moving equipment to the moon, landing on the lunar surface, deploying it, and more is a formidable undertaking. Even the most modest proposal, a Lunar Array for Radio Cosmology (LARC), consists of over a hundred simple design antennas spread over a distance of two kilometers. That would cost more than a billion dollars, just for that, comparable to the most expensive radio stations ever built on Earth.
This shows a particular antenna design that LUNAR is studying. The black X's on the antenna arms are the photon collecting dipoles. The yellow arm is made of a very thin kapton film. The dipoles are connected by an electrical transmission line to the central concentrator, indicated in purple. This hub transmits the data to the Earth.NASA / Lunar University Network for Astrophysical Research / UC Boulder
For almost every conceivable application in astronomy, going to the moon is a place much inferior to the mere superiority of the earth's atmosphere. The extreme temperatures encountered everywhere on the Moon represent an extraordinary challenge beyond any advantage you take from the surface of the Moon. It is only in radio frequencies that the benefits of being on the lunar side provide an opportunity to observe that we can not obtain terrestrial or spatial observations.
Until the costs are reduced or we show that we are ready to pay, it is unlikely that we will see a lunar telescope superior to the other options. The Universe is there, waiting for us to discover its secrets. When we decide that a lunar radio network is worth it, we will go a long way in discovering our cosmic origins.
