(Thought Question) What would a giant far away mirror look like to a telescope?

(Thought Question) What would a giant far away mirror look like to a telescope?

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If there was a theoretically perfect mirror the size of say, our solar system, somewhere out in space that had a focal point of literally earth. What would that look like to a space or earth telescope? Could it be distinguished from other parts of space? Could you identify earth in it? (A la By putting a mirror in space, would we be able to see into the past?)

If there was a theoretically perfect mirror the size of say, our solar system, somewhere out in space…

Great thought experiment so far!

… that had a focal point of literally earth…

Rats! I was hoping for a flat mirror so the answer would have been slightly simpler.

It is true that concave mirrors are "magnifying mirrors" and if we stay closer to the mirror than twice its focal point (see below) we can see a magnified image. I don't believe that it provides better optical resolution than a normal mirror, but since the construction of our eyes is fixed (we can't change the optical system nor "pixel density") we use the mirror to "blow up" the image in the same way that a photographic enlarger blows up the image on a negative without improving the resolution of the image.


In optics image information is encoded in the wavefront at any point whether in focus at that point or not. If we know the mirror's diameter and distance from Earth, we can apply the principle of diffraction in a simple way no matter how complicated the rest of the optical system.

For a hard-edge circular mirror (top-hat shaped apodization) we know that the Airy disk is the right principle to apply, and a simple definition of resolution gives us

$$ heta approx ext{1.22} frac{lambda}{d}$$

for the angular resolution. Let's use 500 nm green light for $lambda$ and twice Neptune's orbital radius (60 AU) for $d$. That gives us $4 imes 10^{-18}$ radians.

If the mirror were at the distance of Proxima Centauri or only $4 imes 10^{+16}$ meters, then the impact on resolving a wavefront from the perfect mirror based only on diffraction of a circular aperture would be of the order of centimeters!

The focal length of a concave mirror is the parallel-to-point distance, so we would really need the mirror to be at roughly the point-to-point distance of twice the focal length.

If the concave mirror brought our image back to us, say on a sheet of paper, it would be incredibly dim i.e. pretty much no photons except from the Sun itself. But if we ignore that then we would see ourselves blurred by about 1 centimeter.

If the image was kilometers in front of us then we could focus a telescope on that image in space and re-image it at the entrance pupil of an eyepiece or on to a sensor.

If the telescope were 1 meter in diameter, we could see roughly a 1 meter wide swath of Earth.

Of course this doesn't work so simply because the mirror would have to be pointed such that the location of Earth 8.5 years ago would be imaged where we were today.


Yes this is kinda possible from a Gedankenexperiment point of view; a 60 AU mirror out at Proxima Centauri with a focal length of twice that distance could produce an image of Earth nearby Earth (light time considerations in force) and we could look at that location in space with a large diameter telescope and see a patch of Earth 8.5 years ago roughly vignetted by the size of the telescope's aperture.

(Thought Question) What would a giant far away mirror look like to a telescope? - Astronomy

The Giant Magellan Telescope will be one member of the next generation of giant ground-based telescopes that promises to revolutionize our view and understanding of the universe. It will be constructed in the Las Campanas Observatory in Chile. Commissioning of the telescope is scheduled to begin in 2029.

The GMT has a unique design that offers several advantages. It is a segmented mirror telescope that employs seven of today’s largest stiff monolith mirrors as segments. Six off-axis 8.4 meter or 27-foot segments surround a central on-axis segment, forming a single optical surface 24.5 meters, or 80 feet, in diameter with a total collecting area of 368 square meters. The GMT will have a resolving power 10 times greater than the Hubble Space Telescope. The GMT project is the work of a distinguished international consortium of leading universities and science institutions.

How will it work?

Light from the edge of the universe will first reflect off of the seven primary mirrors, then reflect again off of the seven smaller secondary mirrors, and finally, down through the center primary mirror to the advanced CCD (charge coupled device) imaging cameras. There, the concentrated light will be measured to determine how far away objects are and what they are made of.

The GMT primary mirrors are made at the Richard F. Caris Mirror Lab at the University of Arizona in Tucson. They are a marvel of modern engineering and glassmaking each segment is curved to a very precise shape and polished to within a wavelength of light—approximately one-millionth of an inch. Although the GMT mirrors will represent a much larger array than any telescope, the total weight of the glass is far less than one might expect. This is accomplished by using a honeycomb mold, whereby the finished glass is mostly hollow. The glass mold is placed inside a giant rotating oven where it is “spin cast,” giving the glass a natural parabolic shape. This greatly reduces the amount of grinding required to shape the glass and also reduces weight. Finally, since the giant mirrors are essentially hollow, they can be cooled with fans to help equalize them to the night air temperature, thus minimizing distortion from heat.

One of the most sophisticated engineering aspects of the telescope is what is known as “adaptive optics.” The telescope’s secondary mirrors are actually flexible. Under each secondary mirror surface, there are hundreds of actuators that will constantly adjust the mirrors to counteract atmospheric turbulence. These actuators, controlled by advanced computers, will transform twinkling stars into clear steady points of light. It is in this way that the GMT will offer images that are ten times sharper than the Hubble Space Telescope’s.

The location of the GMT also offers a key advantage in terms of seeing through the atmosphere. Located in one of the highest and driest regions on earth, Chile’s Atacama Desert, the GMT will have spectacular conditions for more than 300 nights a year. Las Campanas Peak (“Cerro Las Campanas”), where the GMT will be located, has an altitude of over 2,550 meters or approximately 8,500 feet. The site is almost completely barren of vegetation due to lack of rainfall. The combination of seeing, number of clear nights, altitude, weather and vegetation make Las Campanas Peak an ideal location for the GMT.

Why is it being built?

“The essence of our species is to explore — to find new answers and new meaning for who we are.”
—Pat McCarthy, Vice President Emeritus, GMT

Most people do not realize that, as recently as 100 years ago, scientists thought the Milky Way was the entire universe.

But in the 1920s, Edwin Hubble, using the famous 100-inch telescope at Mount Wilson, determined that there were other galaxies too. That discovery was followed by the realization that the universe was expanding. These discoveries revolutionized our view of the universe. The heavens were not static, as had been assumed, but changing over time. Like the 100-inch telescope, perhaps the most exciting and intriguing fact is that the Giant Magellan Telescope promises to make discoveries that we cannot yet imagine.

Perhaps one of the most exciting questions yet to be answered is: are we alone? The Giant Magellan Telescope may help us answer that. Finding evidence of life on other planets would be a momentous discovery—certainly one of the greatest in the history of human exploration. But taking pictures of these so-called “extrasolar” planets, which orbit other stars, is extraordinarily difficult. In addition to the vast distance—the very closest star to earth is four light-years away—the biggest problem is the glare of the host star which blocks out most of the reflected light of a small distant planet.

This is why the great collecting area of the GMT is so important. The GMT mirrors will collect more light than any telescope ever built and the resolution will be the best ever achieved.

This unprecedented light gathering ability and resolution will help with many other fascinating questions in 21st century astronomy. How did the first galaxies form? What are dark matter and dark energy that comprise most of our universe? How did stellar matter from the Big Bang congeal into what we see today? What is the fate of the universe?

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The Future Of Astronomy: The Giant (25 Meter!) Magellan Telescope

Image credit: Giant Magellan Telescope - GMTO Corporation.

Throughout history, there have been four things that have determined just how much information we can glean about the Universe through astronomy:

There have been tremendous advances in ground-based astronomy over the past 25 years, but they've occurred almost exclusively through improvements in criteria 2 through 4. The largest telescope in the world in 1990 was the Keck 10-meter telescope, and while there are a number of 8-to-10 meter class telescopes today, 10 meters is still the largest class of telescopes in existence.

Image credit: Adi Zitrin, California Institute Of Technology, 2015.

Moreover, we've really reached the limits of what improvements in those areas can achieve without going to larger apertures. This isn't intended to minimize the gains in these other areas they've been tremendous. But it's important to realize how far we've come. The charge-coupled devices (CCDs) that are mounted to telescopes can focus on either wide-field or very narrow areas of the sky, gathering all the photons in a particular band over the entire field-of-view or performing spectroscopy -- breaking up the light into its individual wavelengths -- for up to hundreds of objects at once. We can cram more megapixels into a given surface area. Quite simply, we're at the point where practically every photon that comes in through a telescope's mirror of the right wavelength can be utilized, and where we can observe for longer and longer periods of time to go deeper and deeper into the Universe if we have to.

Image credit: the CANDELS UDS Epoch 1 observations image produced by Anton Koekemoer (STScI).

In addition, we've come a long way towards overcoming the atmosphere, without the need to launch a telescope into space. By building our observatories at very high altitudes in locations where the air is still -- such as atop Mauna Kea or in the Chilean Andes -- we can immediately take a large fraction of atmospheric turbulence out of the equation. The addition of adaptive optics, where a known signal (like a bright star, or an artificial star created by a laser that reflects off of the atmosphere's sodium layer, 60 kilometers up) exists but appears blurry, can allow us to create the right "mirror shape" to de-blur that image, and hence all the other light that comes along with it. This way, we can further eliminate the turbulent effects of the atmosphere.

And finally, computational power and data analysis technique have improved tremendously, where more useful information can be recorded and extracted from the same data that we can take. These are tremendous advances, but just like a generation ago, we're still using the same size telescopes. If we want to go deeper into the Universe, to higher resolution, and to greater sensitivities, we have to go to larger apertures: we need a bigger telescope. There are currently three major projects that are competing to be first: the Thirty-Meter Telescope atop Mauna Kea, the (39 meter) European Extremely Large Telescope in Chile, and the (25 meter) Giant Magellan Telescope (GMT), also in Chile. These represent the next giant leap forward in ground based astronomy, and the Giant Magellan Telescope is probably going to be first, having broken ground at the end of last year and with early operations planned to begin in just 2021, and becoming fully operational by 2025.

Image credit: Giant Magellan Telescope / GMTO Corporation.

It's not really technically possible to make a single mirror that large, as the materials themselves will deform at those weights. Some approaches are to use a segmented "honeycomb" shape of mirrors, like the E-ELT plans, with 798 mirrors, but that produces a distinct disadvantage: you get a large number of image artifacts that are difficult to remove where the sharp lines are. Instead, the Giant Magellan Telescope uses just seven mirrors (four are already complete), each a monstrous 8.4 meters (or 28 feet!) in diameter, all mounted together. The circular nature of these mirrors leaves gaps between them, meaning you miss out on a little bit of your light-gathering potential, but the resultant images are much cleaner, easier to work with, and free of those nasty artifacts.

Image credit: Krzysztof Ulaczyk of Wikimedia Commons.

It's also being built on a great site: the Las Campanas Observatory, which currently houses the twin 6.5-meter Magellan telescopes. At an altitude of nearly 2,400 meters (

8,000 feet), with clear skies and devoid of light pollution, it's one of the best places for astronomical observing on Earth. Equipped with the same cutting edge cameras/CCD, spectrograph, adaptive optics, tracking and computerized technology that the world's best telescopes have today -- only scaled up for a 25 meter telescope -- the GMT is going to revolutionize astronomy in a number of tremendous ways.

Image credit: NASA, ESA, and J. Lotz, M. Mountain, A. Koekemoer, and the Hubble Frontier Fields Team . [+] (STScI).

1.) The first galaxies: in order to go deeper into the Universe, you need to not only compensate for the fact that objects that are twice as far away deliver only one quarter of the light to your eyes, but that the expanding Universe causes that light to redshift, or to get stretched to longer wavelengths. Our atmosphere might only let a few select "windows" of light through, but this actually helps us out in some ways: the ultraviolet radiation that gets blocked by our atmosphere from nearby stars like the Sun can get redshifted all the way into the visible (and even near-infrared) portion of the spectrum at great enough distances. Finding these galaxies is easiest from space, but confirming them requires follow-up spectroscopy, which is best done from the ground. Ideally, the combination of the James Webb Space Telescope (last week's "future of astronomy" article) and the GMT -- which can measure the redshift and spectral features of these objects directly and unambiguously -- will push the limits of the most distant known galaxies in the Universe out farther than ever, and give us an unprecedented view of how galaxies form and evolve.

Image credit: M. Kornmesser / ESO.

2.) The first stars: even more exciting is the chance to directly observe and ascertain the properties of the first stars ever to form in the Universe. After the Big Bang, when the Universe forms neutral atoms for the first time, there are no heavy elements at all. There's hydrogen, deuterium, helium-3 and helium-4, and a little bit of lithium-7. That's it. Absolutely nothing else. And so the first stars that formed in the Universe must have been made out of these materials alone, with none of the heavier elements found in 100% of our Milky Way's stars. To find these pristine stars -- these Population III stars -- we have to go to incredibly high redshifts. Whereas today, we've barely uncovered one such candidate for these stars, the GMT should be able to discover hundreds of such candidates. In addition, it won't just discover more, but:

  • it should be able to determine the relative elemental abundances within,
  • could measure the hydrogen, helium, and possibly even deuterium and lithium concentrations,
  • could measure the absorption spectra of the gas clouds between us and them,
  • and can discover them before the Universe has been reionized, back when there's still neutral gas there.

This applies to the first galaxies as well, but is even more exciting for the first stars, enabling us to see pristine samples of the Universe and understand just how big these earliest stars can get.

Image credit: NASA and J. Bahcall (IAS) (L) NASA, A. Martel (JHU), H. Ford (JHU), M. Clampin . [+] (STScI), G. Hartig (STScI), G. Illingworth (UCO/Lick Observatory), the ACS Science Team and ESA (R).

3.) The earliest supermassive black holes: we've serendipitously found a large number of these already, in the form of quasars. The largest number of these have been found by large-volume and all-sky surveys like SDSS and 2dF before it, but in order to truly measure these objects well, we need to obtain their spectra, something GMT will be perfect for. The difference between spectroscopy and photometry is a little bit like the difference between a black-and-white TV and a color TV: they can both show you a picture, but with spectroscopy, the level of detail and the amount of information you get increases more than a thousand-fold, as we can learn what's inside (and how much) via spectroscopy, while without it we can only make assumptions. GMT will not only give us follow-up spectroscopy on what the future EUCLID and WFIRST missions will find -- the most distant quasars over huge regions of the sky -- but will enable us to find more distant quasars (and hence younger, smaller and earlier supermassive black holes) than anything else in (and out of) this world.

Image credit: Ed Janssen, ESO.

4.) The Lyman-alpha forest: when we look at the most distant quasars and galaxies, we not only see that distant light, but we see every intervening gas cloud there is between that object and ourselves, along the line-of-sight. By measuring the absorption features along the way, we can see how the structure and composition of the Universe evolves, which tells us all sorts of things about components of the Universe that would otherwise be invisible, like neutrinos and dark matter.

Of course, there's all the "normal" astronomy we can do with it as well, including planet-finding, understanding stellar and galaxy evolution, measuring supernovae and their remnants, planetary nebulae and star forming regions, clusters, interstellar and intergalactic gas and so much more. Perhaps most exciting will be the advances that we don't know are coming. No one could've predicted that Edwin Hubble would discover the expanding Universe when the 100-inch Hooker telescope was first commissioned no one could've predicted how the Hubble Deep Field would open up the Universe when that image was first taken. What will GMT find in the ultra-distant Universe?

Image credit: Omar Almaini, Nottingham University (P.I. of the Ultra-Deep Survey).

This is why we look, and this is what science at the frontiers is. The Giant Magellan Telescope will do all the things from the ground that space-based telescopes can't do as well, and will do them better than any other telescope in existence. Unlike the other large ground-based telescopes planned, it's completely privately funded, there are no political controversies over it, and construction on it has already begun. The future of any scientific endeavor -- and perhaps astronomy in particular -- requires you to be ambitious, and to invest in looking for the unknown. We'll never learn what lies beyond our current frontiers of knowledge unless we search, and the GMT is one major step towards looking where no one has ever looked before.

Figuring for Yourself

25: What is the area, in square meters, of a 10-m telescope?

26: Approximately 9000 stars are visible to the naked eye in the whole sky (imagine that you could see around the entire globe and both the northern and southern hemispheres), and there are about 41,200 square degrees on the sky. How many stars are visible per square degree? Per square arcsecond?

27: Theoretically (that is, if seeing were not an issue), the resolution of a telescope is inversely proportional to its diameter. How much better is the resolution of the ALMA when operating at its longest baseline than the resolution of the Arecibo telescope?

28: In broad daylight, the size of your pupil is typically 3 mm. In dark situations, it expands to about 7 mm. How much more light can it gather?

29: How much more light can be gathered by a telescope that is 8 m in diameter than by your fully dark-adapted eye at 7 mm?

30: How much more light can the Keck telescope (with its 10-m diameter mirror) gather than an amateur telescope whose mirror is 25 cm (0.25 m) across?

31: People are often bothered when they discover that reflecting telescopes have a second mirror in the middle to bring the light out to an accessible focus where big instruments can be mounted. “Don’t you lose light?” people ask. Well, yes, you do, but there is no better alternative. You can estimate how much light is lost by such an arrangement. The primary mirror (the one at the bottom in [link]) of the Gemini North telescope is 8 m in diameter. The secondary mirror at the top is about 1 m in diameter. Use the formula for the area of a circle to estimate what fraction of the light is blocked by the secondary mirror.

32: Telescopes can now be operated remotely from a warm room, but until about 25 years ago, astronomers worked at the telescope to guide it so that it remained pointed in exactly the right place. In a large telescope, like the Palomar 200-inch telescope, astronomers sat in a cage at the top of the telescope, where the secondary mirror is located, as shown in [link]. Assume for the purpose of your calculation that the diameter of this cage was 40 inches. What fraction of the light is blocked?

33: The HST cost about ?1.7 billion for construction and ?300 million for its shuttle launch, and it costs ?250 million per year to operate. If the telescope lasts for 20 years, what is the total cost per year? Per day? If the telescope can be used just 30% of the time for actual observations, what is the cost per hour and per minute for the astronomer’s observing time on this instrument? What is the cost per person in the United States? Was your investment in the Hubble Space telescope worth it?

34: How much more light can the James Webb Space Telescope (with its 6-m diameter mirror) gather than the Hubble Space Telescope (with a diameter of 2.4 m)?

35: The Palomar telescope’s 5-m mirror weighs 14.5 tons. If a 10-m mirror were constructed of the same thickness as Palomar’s (only bigger), how much would it weigh?



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Today Phil explains how telescopes work and offers up some astronomical shopping advice.

How Telescopes Work 1:07
Refractors vs Reflectors 2:50
Technology and the Light Spectrum 7:45

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Picking the Best Observing Sites

A telescope like the Gemini or Keck telescope costs about ?100 million to build. That kind of investment demands that the telescope be placed in the best possible site. Since the end of the nineteenth century, astronomers have realized that the best observatory sites are on mountains, far from the lights and pollution of cities. Although a number of urban observatories remain, especially in the large cities of Europe, they have become administrative centers or museums. The real action takes place far away, often on desert mountains or isolated peaks in the Atlantic and Pacific Oceans, where we find the staff’s living quarters, computers, electronic and machine shops, and of course the telescopes themselves. A large observatory today requires a supporting staff of 20 to 100 people in addition to the astronomers.

The performance of a telescope is determined not only by the size of its mirror but also by its location. Earth’s atmosphere, so vital to life, presents challenges for the observational astronomer. In at least four ways, our air imposes limitations on the usefulness of telescopes:

  1. The most obvious limitation is weather conditions such as clouds, wind, and rain. At the best sites, the weather is clear as much as 75% of the time.
  2. Even on a clear night, the atmosphere filters out a certain amount of starlight, especially in the infrared, where the absorption is due primarily to water vapor. Astronomers therefore prefer dry sites, generally found at high altitudes.
  3. The sky above the telescope should be dark. Near cities, the air scatters the glare from lights, producing an illumination that hides the faintest stars and limits the distances that can be probed by telescopes. (Astronomers call this effect light pollution.) Observatories are best located at least 100 miles from the nearest large city.
  4. Finally, the air is often unsteady light passing through this turbulent air is disturbed, resulting in blurred star images. Astronomers call these effects “bad seeing.” When seeing is bad, images of celestial objects are distorted by the constant twisting and bending of light rays by turbulent air.

The best observatory sites are therefore high, dark, and dry. The world’s largest telescopes are found in such remote mountain locations as the Andes Mountains of Chile ([link]), the desert peaks of Arizona, the Canary Islands in the Atlantic Ocean, and Mauna Kea in Hawaii, a dormant volcano with an altitude of 13,700 feet (4200 meters).

Figure 6. Cerro Paranal, a mountain summit 2.7 kilometers above sea level in Chile’s Atacama Desert, is the site of the European Southern Observatory’s Very Large Telescope. This photograph shows the four 8-meter telescope buildings on the site and vividly illustrates that astronomers prefer high, dry sites for their instruments. The 4.1-meter Visible and Infrared Survey Telescope for Astronomy (VISTA) can be seen in the distance on the next mountain peak. (credit: ESO)

Giant Hawaii telescope to focus on big unknowns of universe

This undated file illustration provided by Thirty Meter Telescope (TMT) shows the proposed giant telescope on Mauna Kea on Hawaii’s Big Island. Construction on giant telescope to start again in the third week of July 2019, after court battles over Hawaii site that some consider sacred. (TMT via AP, File)

HONOLULU &mdash Is there life on planets outside our solar system? How did stars and galaxies form in the earliest years of the universe? How do black holes shape galaxies?

Scientists are expected to explore those and other fundamental questions about the universe when they peer deep into the night sky using a new telescope planned for the summit of Hawaii&rsquos tallest mountain.

But the Thirty Meter Telescope is a decade away from being built. And Native Hawaiian protesters have tried to thwart the start of construction by blocking a road to the mountain. They say installing yet another observatory on Mauna Kea&rsquos peak would further defile a place they consider sacred.

Activists have fought the $1.4 billion telescope but the state Supreme Court has ruled it can be built. The latest protests could be the final stand against it.

Here&rsquos a look at the telescope project and some of the science it&rsquos expected to produce.


The large size of the telescope&rsquos mirror means it would collect more light, allowing it to see faint, far-away objects such as stars and galaxies dating back as long as 13 billion years.

The telescope gets its name from the size of the mirror, which will be 30 meters (98 feet) in diameter. That&rsquos three times as wide as the world&rsquos largest existing visible-light telescope.

Adaptive optics would correct the blurring effects of the Earth&rsquos atmosphere.

The telescope would be more than 200 times more sensitive than current telescopes and able to resolve objects 12 times better than the Hubble Space Telescope, said Christophe Dumas, head of operations for the Thirty Meter Telescope.


&mdash Distant planets. During the past 20 years, astronomers have discovered it is common for planets to orbit other stars in the universe. But they don&rsquot know much about what those planets &mdash called extrasolar planets or exoplanets &mdash are like. The new telescope would allow scientists to determine whether their atmospheres contain water vapor or methane which might indicate the presence of life.

&ldquoFor the first time in history we will be capable of detecting extraterrestrial life,&rdquo Dumas said.

Dumas said the new telescope would use special optics to suppress the light of stars. He compared the technique to blocking a bright street light in the distance with your thumb then seeing insects circling in the fainter light below.

&mdash Black holes. Black holes at the center of most galaxies are so dense that nothing, not even light, can escape their gravitational pull.

Andrea Ghez, a University of California, Los Angeles physics and astronomy professor who discovered our galaxy&rsquos black hole, said scientists believe black holes play a fundamental role in how galaxies are formed and evolve.

But so far astronomers have only been able to observe this dynamic in detail in the Milky Way because the next galaxy is 100 times farther away.

The Thirty Meter Telescope would enable scientists to study more galaxies and more black holes in greater detail.

It may also help them understand gravity. Those who doubt the importance should note that GPS-enabled maps on cellphones rely on Einstein&rsquos theories about gravity.

&ldquoWe think of these things as esoteric. But in fact, in the long run, they have profound impacts on our lives,&rdquo Ghez said.

&mdashDark matter and dark energy. Humans see only about 4 percent of all matter in the universe, Dumas said. Dark energy makes up about three-quarters and dark matter the rest. Neither can be seen.

&ldquoWe have no idea what dark matter is and no idea what dark energy is. That&rsquos a big dilemma in today&rsquos world,&rdquo Dumas said.

Because mass deforms space and light, Dumas said the new telescope would make it possible to measure how dark matter influences light.

It could do this by studying light from far-away galaxies. The light would take different paths to the telescope, generating different images of the same object.

The weather at the summit of Mauna Kea tends to be ideal for viewing the skies. At nearly 14,000 feet, its peak is normally above the clouds. Being surrounded by the ocean means air flows tend to be smoother and it has the driest atmosphere of any of the candidate sites.

The mountain is already home to 13 other telescopes.

Ghez used the Keck Observatory there to find our galaxy&rsquos black hole. Other discoveries credited to those sites over the years include the first images of exoplanets and the detection of &lsquoOumuamua, the first object from interstellar space, which turned out to be a comet from a distant star system.


Two other giant telescopes are being built in Chile, which also has excellent conditions for astronomy.

The European Extremely Large Telescope will have a primary mirror measuring 39 meters, or 128 feet, in diameter. The Giant Magellan Telescope&rsquos mirror will be 24.5 meters, or 80 feet, in diameter.

The Thirty Meter Telescope is the only one expected to be built in the Northern Hemisphere. Because different spots on Earth look out on different parts of the sky, the next-generation ground telescopes will ensure scientists are able to see the entire universe.

The universities and national observatories behind the Thirty Meter Telescope have selected Spain&rsquos Canary Islands as a backup site in case they are unable to build in Hawaii.

The Future of Telescopes Is Looking Bigger and Brighter Than Ever

Astronomy has come a long way in the 405 years since Galileo's historic first survey of the night sky over Florence in 1609. The next generation of terrestrial telescopes are set to peer deeper into the cosmos and further back in time than ever before. We sat down with Dr. Patrick McCarthy, Director of the Giant Magellan Telescope Organization, to find out just how far the field has advanced and where it might be headed.

McCarthy: Optics, as we're familiar with them, began in part because the people of Venice who were building on the technology of traditional Roman glass making—all ancient glasses were opaque, deeply colored, you couldn't see through it—but on the island of Milano, they first learned how to make glass that was transparent. And once you have transparent glass with any kind of curvature to it, you can immediately see that it magnifies light and distorts images. That led to the invention of lenses and spectacles, but it wasn't until a glassmaker in Holland by the name of Lippershey was preparing two lenses and lined them up—one at arms length, the other just in front of his nose—and realized that they made distant objects appear much bigger. He and others began mounting these lenses in pairs to make telescopes.

In 1609, Galileo built his own telescope and has the inspiration to not point it at distant trees and buildings but up to the heavens. It was pretty audacious to point a telescope up at a star in those days and think you might see something but he quickly changed the whole world and the whole history of science by realizing that the universe was a very different place than we thought. So by taking a piece of technology and repurposing it for a new task, he changed the history of the world. And that was really the first step in the path of building telescopes and its been that same approach in the four centuries since.

Gizmodo: And so where does this path lead?

McCarthy: It's funny because every generation, when people build the newest "biggest telescope", they end up saying "we'll never build one bigger than this. This is the end of the line of the technology, we'll never be able to top this." And, of course, someone from the next generation of young people come along, and they find a new way forward.

So in the history of telescopes like Galileo's, they learned to make telescopes that were larger. they quickly found out that a limitation to the simple lense—that is, a single piece of glass—was that they make images in different places in different colors. So if you look through a simple lense and you look at a star, or just a lamp post, you see a spread of color [the halo effect - ed.] that makes it very difficult to take sharp images. And it was because of this that people figured out how to make pairs of lenses out of different types of glass that cancel out the chromatic aberration. If you buy a camera lense today, it might have five or six different lenses, each with different types of glass, and they're all there to ensure that all wavelengths of color come into focus at the same point. That was a major breakthrough, figuring out how to make lenses that were achromatic, and that led to a huge growth in refracting telescopes—those based on lenses—but around 1860 or so it became evident that lenses of a certain size, those bigger than about a meter (36 - 40 inches) in diameter, tend to sag and break under their own weight. That was really the end of the line of that technology.

But not long after Galileo, Isaac Newton—who was also a pretty smart guy—realized that you can bend light in reflections as well as in transmissions. So you made a telescope based on mirrors rather than lenses. But that avenue of Astronomy technology sat dormant for centuries, but as people saw the limitations of lense-based telescopes, they began to build them with mirrors instead.

Around 1890 was the crossover, where bigger telescopes were made from reflecting surfaces rather than lenses but a big issue with reflecting telescopes is that when you polish a piece of metal, it tends to oxidize and tarnish. So people were looking around ofr a type of metal that was shiny, pretty strong, and inexpensive and they came up with an alloy called speculum metal—its an alloy of brass, tin and copper. you can polish it but it tarnishes in just a few days so astronomers at the time had to re polish their mirrors every two or three days which was very hard work.

The next breakthrough came when someone decided to take the best of both worlds, combining the glass used for lenses and mounting reflective metal on top of the glass. You would grind the glass into the shape of a mirror and then deposit a surface of silver on top of it. That way you get all the control and the properties of glass but made shiny like a mirror. That really set us on the path towards modern astronomy—all astronomical telescopes since the mid-19th century have been metal-on-glass.

This led to another period of rapid growth around 1800, especially here in Southern California at Mt Wilson with the first 40, 60 and 100 inch telescopes, and the 200-incher at Mt Palomar. But eventually we again hit the limit of what the technology can do. Glass mirrors couldn't be made bigger than about 8 meters in diameter or else, like the earlier lenses, they would distort and break under their own weight. So people realized that if you want to make a really big telescope, youɽ have to combine multiple mirrors into a single focal surface.

That turned out to be a technical challenge, but was solved first with the Keck telescope in the 1990s and we're now doing it with the GMT, using a small number of very large mirrors—much like Newton's—and we're now building the James Webb space telescope which uses the same kind of technology as well (but using metal on beryllium to make "single-lightwave" mirrors), which we call a segmented mirror telescope.

The thinking now is that there really is no limit on how big you can make a segmented mirror telescope so long as you have the room to put it into a support structure, so we're in this fascinating period of technology now that has no obvious bounds. There are financial challenges, engineering challenges but we think we've found a sweet spot with the GMT where we can make a mirror that's 10 times larger than any mirror to date with three times the angular resolution as the Hubble space telescope. And like galileo who used his lenses to examine Jupiter's moons, we'll use the GMT to image planets orbiting other stars. so we'll look at stars nearbgy our solar system, 10s of light years away, to see the planets that orbit those stars. Do they look like our solar system? And our solar system is really very simple—Jupiter has most of the mass of the solar system—in terms of planets—and then a bunch of rocky planets like Mars, Venus, and Earth inside Jupiter's orbit and a few snowballs on the outer edge of the solar system.

But we have suspicions that solar systems outside our own may have planets the mass of jupiter but with the orbit of mercury. So there's a whole universe of solar system configurations that we know very little about. GMT and other similar telescopes will allow us to look at them—much like Galileo but with modern instrumentation to actually see the structure of the planets themselves. And that's what we've been waiting for: to see other worlds and answer the question, "Are we special, are we alone? Or are we just commonplace among the galaxies and the universe is filled with planets and filled with life?" If I had to bet, Iɽ bet on the latter but Iɽ be that life is much more diverse than we suspect because the planetary systems are much more diverse than our own solar system.

We will be able to use the GMT, the Hubble, and the James Webb to look so far out into space that, due to the finite speed of light that we will look back in time. So if we look back far enough we can see the universe in its very infant stages—we should be able to see the first galaxies that formed, perhaps even the first stars so the telescope is in a very real sense a time machine and the GMT will allow us to look back to the very early days of the universe, just shortly after the big bang when the universe as we know it came into being, and that's a pretty profound thing to do.

Gizmodo: Given that telescope technology doesn't have a theoretical limit, only engineering and financial as you mentioned earlier, do you feel the future of deep space imaging will be primarily terrestrial, space-based, or a combination of the two?

McCarthy: I hope we'll continue to see a balances of the two. While the Hubble has been spectacularly successful, without the big telescopes on the ground taking the spectra, measuring chemical abundances—all the really core astrophysics aspects. One of the biggest challenges to space-based telescopes is that they're extraordinarily expensive and there's a severe limit on the amount of mass that you can effectively lift into orbit. It costs between 500 and 1000 times as much to build a telescope in space as it does to build one on the ground of the same size.

Adaptive optics is a game changer. It allows us to achieve space-like resolution on the ground. So what we see is an increasing divergence between space telescopes and terrestrial ones. Large ground telescopes like the GMT are approaching 30 meters while space telescopes are barely breaking 6 meters—there's a crazy gap between ground and space. We'll likely see future space telescopes utilized only for the stuff we absolutely can't image from the ground—primarily because the Earth's atmosphere appears opaque in the Ultraviolet, some parts of the infrared, and just unbearably bright in the thermal range. So if you're trying to image at a wavelength of 100 microns from a ground telescope, you'll see the sky glowing, the ground glowing, everything's bright. But if you put that telescope in space and cool it down and its imaging capability is unmatched so its a matter of how you balance the technology. I foreseen visible and near infrared from the ground and thermal infrared and ultraviolet from space.

Gizmodo: When the GMT does begin to produce data, what will be done with it?

McCarthy: The GMT itself will be be made available to scientists based on a peer-review process. There will be a call for proposals, these proposals will be reviewed by other astronomers and the most promising proposals will be given time on the telescope. Those researchers will go to Chile, do their time on the telescope, publishing their findings in the open and scientific literature but at the same time all their data goes into a scientific archive where it is preserved, organized, and curated. Anyone can use that data for their own scientific purposes.

Gizmodo: And how much data do you expect to produce?

McCarthy: Our data rates are actually pretty modest— it's primarily because we're looking at things that are very faint and very far away. We'll look at the same object for hours at a time so we'll only produce between 10 and 20 gigabytes a night, maybe 30 to 40 terabytes a year. In terms of big data, it's not really a driver, more for the quality and uniqueness of the data. Other facilities that are all about surveying large areas of the sky in a short period of time, they will produce petabytes a year but if you want to find those special objects, you just can't do it at any other sort of facility.

Giant Hawaii telescope will dive into the big unknowns of the universe

/>In this Sunday, July 14, 2019, file photo, a telescope at the summit of Mauna Kea, Hawaii's tallest mountain is viewed. Astronomers using a giant telescope planned for Hawaii's tallest peak will be able to study how the earliest galaxies formed not long after the Big Bang more than 13 billion years ago, which will inform humanity's understanding of how the universe came to be what it is today. They will be able to study planets orbiting stars other than our own with much greater detail. (AP Photo/Caleb Jones, File)

In this Sunday, July 14, 2019, file photo, a telescope at the summit of Mauna Kea, Hawaii's tallest mountain is viewed. Astronomers using a giant telescope planned for Hawaii's tallest peak will be able to study how the earliest galaxies formed not long after the Big Bang more than 13 billion years ago, which will inform humanity's understanding of how the universe came to be what it is today. They will be able to study planets orbiting stars other than our own with much greater detail. (AP Photo/Caleb Jones, File)

I mean, if we can see the big bang as background radiation, isn't it basically seeing ourselves in the past in a way?
I don't know, sorry if it's a stupid question.

The stuff that we're seeing in the distant past is also really far away. To see something, say, a billion years ago, it has to be far enough away that its light traveled toward us for a billion years. So we're not seeing our own past, we're seeing the past of other stuff.

We can't see our own past this way because the light from our past is moving away from us, so we'll never see it.

So theoretically, if we could instantaneously teleport or pop through a wormhole to some point 4.5 billion light-years away, and had the tech to view our solar system from that distance, then we could actually observe a newly formed Earth (i.e. look into our own past)

I have another question - so an object 1 billion light years away, we’re seeing it as it was 1 billion years ago, because it took the light 1 billion light years for that light to reach us. That’s all logical.

But due to the continued expansion of the universe and the growing distance between celestial bodies that comes with that, is there time dilation that affects time scales on observed celestial bodies, similar to the Doppler effect when an object is moving away from you? So if i were to stare at an object 1b ly away for 1 minute, am I really getting 1minute of time passage as experienced by the distant object, or am I getting only maybe 50s of information. Or is this accounted for in the red shifting of light?