Aeronautics researchers generate cracks that move as fast as the speed of sound, and resemble certain earthquake shear ruptures

PASADENA-When a brittle material breaks, the resulting cracks tend to spread quite rapidly. Anyone who has inadvertently subjected a favorite vase to "floor stress" can attest to this.

But exactly how fast a crack can move has been a subject of debate for some time. To understand how fast is fast, one has to know how quickly stress waves spread. In a solid material, waves spread with two speeds-the slower shear waves move at the shear wave speed, and the faster pressure waves move at the pressure wave speed, also commonly known as the speed of sound in the material.

The researchers who specialize in the topic have thought that cracks move at speeds substantially slower than either of these wave speeds in the material (usually less than 20 percent of the speed of sound).

But new work from California Institute of Technology researchers shows that a certain type of crack can exceed the shear wave speed through the material, creating a sort of "sonic boom," and can almost reach sound speed.

According to Ares Rosakis, professor of aeronautics and applied mechanics, such a crack (called a shear crack) can be generated under controlled circumstances and photographed with ultrahigh-speed equipment capable of taking two million photographs in a second. The pictures show a crack with angled shock waves (Mach cones) that closely resemble photographs of a supersonic bullet breaking the sound barrier.

Click here to view or download the high speed photographs showing the propegation of shear cracks (QuickTime format, 2MB)

This result has practical applications, Rosakis says, because there is reason to believe that certain earthquakes can arise from similar shear breakages. A better understanding of the way in which these cracks get rolling could help seismologists with their models of earthquakes along shear faults, Rosakis believes.

To test the idea, Rosakis and his graduate students Omprakash Samudrala and Demirkan Coker bonded two sheets of a clear polyester material called "Homalite." They introduced a notch along the bond line, and rammed the bottom sheet from the side with a steel projectile moving only at 25 meters per second (56 miles per hour). High-speed photographs of the event showed a shear crack starting from the notch tip and accelerating almost up to the sound speed in the material.

The Rosakis team used this particular setup because a fault zone itself is the weak link between two planes. So if the shearing force along a fault plane indeed sets up shear cracks, then the act of breaking two weakly bonded Homalite plates by sliding them apart would be very similar dynamically.

The high-speed photographs indeed show that shear cracks propagate along the bond line at about 2,200 meters per second (5,000 miles per hour). Further, the Mach cones were clearly visible because the cracks were outrunning material shear wave speed, just as a bullet from a high-powered rifle outruns the speed of sound in air. In fact, these shear cracks are faster than speeding bullets and also faster than the fastest supersonic jet planes!

"I believe processes like that have to do with certain events that may happen in the earth's crust. They may also be very relevant to the way that layered solids or composites, involving bonds, fail when subjected to impact loading," says Rosakis. "This is the first lab demonstration that shows these phenomena are possible."

The work is being published this week in the May 21 issue of the journal Science. Samudrala and Coker, both Caltech graduate students in aeronautics, are the other authors of the paper.

This work has been sponsored by the Office of Naval Research and the National Science Foundation.

Robert Tindol

A unique class of neurons in humans and apes that may participate in cognition, volition, and self-awareness discovered by researchers

PASADENA-Clusters of large neurons found exclusively in the brains of humans and other primates closely related to humans may provide these species with enhanced capacities for solving hard problems, as well as for self-control and self-awareness.

In the April 27 issue of Proceedings of the National Academy of Science, neurobiologists Patrick Hof from Mount Sinai and John Allman from Caltech and their colleagues have found an unusual type of neuron, that is likely to be a recent evolutionary acquisition.

The neurons in question are spindle-shaped cells, which are almost large enough to be seen with the naked eye. Their location in the brain is in the frontal lobe near the corpus callosum, which connects the two halves of the brain.

Allman, the Hixon Professor of Psychobiology and professor of biology; Hof; and their team studied 28 different species of primates and found the spindle neurons only in humans and very closely related apes. The concentration of spindle neurons was greatest in humans, somewhat less in chimpanzees, still less in gorillas, and rare in orangutans.

According to Allman, "This declining concentration matches the degree of relatedness of these apes to humans." There were no spindle cells in gibbons, which are small apes, or in of any of the other 22 species of monkey or prosimian primates they examined. The spindle cells were also absent in 20 nonprimate species examined including various marsupials, bats, carnivores and whales.

The cells in question are found in an area of the brain already linked to psychiatric diseases. According to Allman, "In brain imaging studies of depressed patients, there is less neuronal activity in the region and the volume of the area is smaller. The activity of the area is increased in obsessive compulsive patients."

The activity of the area has been shown to increase with the difficulty of the cognitive task being performed. This suggests that the area enhances the capacity to do hard thinking. Activity is also increased when a subject withholds a response or focuses its attention, suggesting the area is involved in self-control.

Furthermore, the spindle neurons themselves are especially vulnerable to degeneration in Alzheimer's disease, which is characterized by diminished self-awareness. From this Allman suggests, "Part of the neuronal susceptibility that occurs in the brain in the course of age-related dementing illnesses may have appeared only recently during primate evolution."

Robert Tindol

Caltech biologists reveal structure of protein responsible for weight loss in cancer and AIDS patients

PASADENA-Caltech biologists have determined the three-dimensional structure of a protein that causes wasting in cancer and AIDS patients. The discovery could lead to new strategies for controlling weight loss in patients with devastating illnesses-and conversely, perhaps new strategies for fighting obesity.

The protein is commonly known as ZAG and is found in most bodily fluids. But researchers have been aware for some time that the protein is particularly abundant in patients who have cancer.

More recently, researchers have discovered that the protein is involved in the wasting syndrome known as cachexia, which is associated with both cancer and AIDS.

"This protein has something to do with fat metabolism," says Pamela Bjorkman, a professor of biology at Caltech and associate investigator of the Howard Hughes Medical Institute. Bjorkman and her team recently published a paper in the journal Science showing ZAG's structure.

One of the most noteworthy features of the structure is the resemblance between ZAG and a family of proteins known as class I major histocompatibility complex molecules, or MHC.

"MHC proteins have a large groove that binds a peptide derived from a pathogen," says Bjorkman, explaining that their new picture of the ZAG crystal shows an unexpected blob in the ZAG counterpart of the MHC peptide binding grove.

"It's not a peptide, but some organic molecule," she says. "We suspect that it is involved in the function of ZAG. If this compound is involved in breaking down lipids, then maybe you could design a drug that replaces it and interfere with lipid breakdown."

According to Bjorkman, other research shows that tumor cells themselves seem to stimulate the body to overproduce ZAG somehow, which in turn leads to the breakdown of body fat.

Thus, people suffering from cachexia don't lose body weight because they don't eat, but because the fat in their bodies is ultimately destroyed by an interaction involving ZAG.

An intervention to stop the wasting, then, might be to disrupt the overexpression of ZAG, and this might be accomplished with monoclonal antibodies or small molecules that bind to ZAG, she says.

The research appeared in the March 19 issue of Science, and was also the subject of an article in HHMI news, published by the Howard Hughes Medical Institute.

The other authors of the paper are Luis Sanchez and Arthur Chirino, both senior research fellows in Bjorkman's lab.

Robert Tindol

Caltech Question of the Month: What causes the auroral lights?

Submitted by Catherine E. Wendt, Pasadena, California.

Answered by Paul Wennberg, associate professor of atmospheric chemistry and environmental engineering science, Caltech.

Ions and electrons produced in the sun's atmosphere form the "solar wind." This stream of charged particles interacts with Earth's magnetic field and impacts the atmosphere in the region called the aurora oval. In the northern hemisphere, the collisions produce a wonderful light show called the aurora borealis. In the southern hemisphere the phenomenon is known as the aurora australis. The light, best observed near the fall or spring equinox, is produced when atmospheric gases that have been excited by these collisions, relax back to their normal states in a process known as fluorescence.

The color and altitude of the aurora tell us which atmospheric gases are being excited. Below 100 kilometers in altitude, nitrogen is responsible for blue and red auroral light. Between 100 and 200 kilometers, green light is produced by oxygen atoms, while above 200 kilometers, red light from oxygen dominates the auroral light.

Much more information, and beautiful photos, can be found at "The Aurora Page,"


Caltech observes brightest gamma-ray burst so far

PASADENA-An extraordinarily bright cosmic gamma-ray flash turns out to be the most energetic one measured so far, according to a team of astronomers from the California Institute of Technology.

"The burst appeared to be more luminous than the whole rest of the universe, and that would be very hard to explain by most current theories,"said Caltech professor of astronomy and planetary science Shrinivas Kulkarni, one of the principal investigators on the team.

"It was ten times more luminous than the brightest burst seen so far, and that was quite unexpected."

"If the gamma rays were emitted equally in all directions, their energy would correspond to ten thousand times the energy emitted by our sun over its entire lifetime so far, which is about 5 billion years," said Caltech professor of astronomy S. George Djorgovski, another of the principal investigators on the team. "Yet the burst lasted only a few tens of seconds."

Gamma-ray bursts are mysterious flashes of high-energy radiation that appear from random directions in space and typically last a few seconds. They were first discovered by U.S. military Vela satellites in the 1960s. Since then, over a hundred theories of their origins have been proposed, but the causes of gamma-ray bursts remain unknown. Some theorists believe that the bursts originate during the formation of black holes.

NASA's Compton Gamma-Ray Observatory satellite has detected several thousand bursts so far. The chief difficulty in studying these puzzling flashes is in locating them precisely enough and quickly enough to follow up with ground-based telescopes.

A breakthrough in this field was made in early 1997 by the Italian/Dutch satellite BeppoSAX, which can locate the bursts with a sufficient accuracy. A team of Caltech astronomers was then able to establish that the bursts originate in the very distant universe. Since then, about a dozen bursts have been studied in detail by astronomers using ground-based telescopes.

The bursts may last only a few seconds in gamma rays, but leave more long-lived but rapidly fading afterglows in X-rays, visible light, and radio waves, which can be studied further.

This burst, called GRB 990123, was discovered by the BeppoSAX satellite on January 23. It was the brightest burst seen so far by this satellite, and one of the brightest ever seen by NASA's Compton Gamma-Ray Observatory.

Within three hours of the burst, members of the Caltech team, including senior postdoctoral scholar in astronomy Stephen Odewahn and graduate students Joshua Bloom and Roy Gal, used Palomar Observatory's 60-inch telescope to discover a rapidly fading visible-light afterglow associated with the burst.

"This adventure began at 5 a.m. with a wake-up call from our Italian friends alerting us about their burst detection," said Bloom, "But it was certainly worth it. We got to watch a remarkable fireworks show!"

A comparison of images obtained at Palomar Observatory. The image on the top is from the Palomar Observatory's digital sky survey (DPOSS). The image on the bottom is the discovery image obtained by S. C. Odewahn and J. S. Bloom.

Following the Caltech team's announcement, several hours later a team of astronomers known as the ROTSE collaboration, led by Professor Carl Akerloff of the University of Michigan, reported that the visible light counterpart of the burst was also seen in the images taken with a small, robotic telescope operated by their team, starting only 22 seconds after the burst. This was the first time that such rapid measurement of a burst afterglow was made, and its extreme brightness was unexpected.

Meanwhile, a new radio source, coincident with the visible-light afterglow discovered at Palomar, was found at the National Radio Astronomy Observatory's Very Large Array radio telescope, near Socorro, New Mexico, by Dale Frail and Kulkarni.

Such a radio flash was predicted by Dr. Re'em Sari, a theorist at Caltech, and Dr. Tsvi Piran (now at Columbia University), and it provides an important input for theories of gamma-ray bursts.

At the prompting of the Caltech team, a group of astronomers led by Professor Garth Illingworth of the University of California at Santa Cruz, used the W. M. Keck Observatory's 10-meter Keck-II telescope at Mauna Kea, Hawaii, to obtain a spectrum of the burst afterglow.

A distance to the burst was determined from its spectrum, and the burst was found to be about 9 billion light-years from Earth.

The Keck measurement of the distance was crucial. "We were stunned," said Djorgovski. "This was much further than we expected, and together with the observed brightness of the burst it implied an incredible luminosity.

"The peak brightness of the visible light afterglow alone would be millions of times greater than the luminosity of an entire galaxy, and thousands of times brighter than the most luminous quasars known."

This remarkable light flash contained only a small fraction of the total burst energy in the gamma rays. Caltech astronomers note that even more energy was likely emitted in forms that are difficult to observe, such as gravitational waves or neutrinos, elusive particles that can penetrate the entire planet Earth without stopping.

As the burst's afterglow faded, the Caltech team discovered a faint galaxy adjacent to it in the sky, in infrared images obtained with the W. M. Keck Observatory's 10-meter Keck-I telescope at Mauna Kea.

This is almost certainly the galaxy in which the burst originated. The galaxy is about as faint as an ordinary 100-watt lightbulb would be if seen from a distance of half a million miles, about twice the distance to the moon.

Subsequently, following a proposal by the Caltech team and others, the Hubble Space Telescope obtained visible-light images of this galaxy and the burst's afterglow. The analysis of these images by the Caltech team indicates that the galaxy is not unusual in its properties, compared to other normal galaxies at comparable distances from Earth.

A detailed follow-up study of the burst's afterglow by the Caltech team revealed a change in its brightness that could be interpreted as a sign of a jet of energy, moving close to the speed of light, and pointing nearly toward Earth.

"This was the first time that such behavior was seen in a gamma-ray burst," emphasized Kulkarni, "and it may help explain in part its enormous apparent brightness."

Scientists are still debating whether such a powerful beaming of energy occurs in gamma-ray bursts.

The team's findings appear in the April 1 issue of the scientific journal Nature, and in a forthcoming issue of the Astrophysical Journal Letters.

In addition to Kulkarni, Djorgovski, Odewahn, Sari, Bloom, and Gal, the Caltech team also includes Professors Fiona Harrison and Gerry Neugebauer, Drs. Chris Koresko and Lee Armus, and several others.


Robert Tindol

Earth's water probably didn't come from comets, Caltech researchers say

PASADENA—A new Caltech study of comet Hale-Bopp suggests that comets did not give Earth its water, buttressing other recent studies but contrary to the longstanding belief of many planetary scientists.

In the March 18 issue of Nature, cosmochemist Geoff Blake and his team show that Hale-Bopp contains sizable amounts of "heavy water," which contains a heavier isotope of hydrogen called deuterium.

Thus, if Hale-Bopp is a typical comet, and if comets indeed gave Earth its water supply billions of years ago, then the oceans should have roughly the same amount of deuterium as comets. In fact, the oceans have significantly less.

"An important question has been whether comets provided most of the water in Earth's oceans," says Blake, professor of cosmochemistry and planetary science at Caltech. "From the lunar cratering record, we know that, shortly after they were made, both the moon and Earth were bombarded by large numbers of asteroids or comets.

"Did one or the other dominate?"

The answer lies in the Blake team's measurement of a form of heavy water called HDO, which can be measured both in Earth's oceans using mass spectrometers and in comets with Caltech's Owens Valley Radio Observatory (OVRO) Millimeter Array. Just as radio waves go through clouds, millimeter waves easily penetrate the coma of a comet.

This is where cosmochemists can get a view of the makings of the comet billions of years ago, before the sun had even coalesced from an interstellar cloud. In fact, the millimeter-wave study of deuterium in water and in organic molecules in the jets emitted from the surface of the nucleus shows that Hale-Bopp is composed of 15 to 40 percent primordial material that existed before the sun formed.

The jets are quite small in extent, so the image clarity provided by the OVRO Millimeter Array was crucial in the current study. "Hale-Bopp came along at just the right time for our work," Blake says. "We didn't have all six telescopes in the array when Halley's comet passed by, and Hyakutake was a very small comet. Hale-Bopp was quite large, and so it was the first comet that could be imaged at high spatial and spectral resolution at millimeter wavelengths."

One other question that the current study indirectly addresses is the possibility that comets supplied Earth with the organic materials that contributed to the origin of life. While the study does not resolve the issue, neither does it eliminate the possibility.

Also involved in the Nature study are Charlie Qi, a graduate student in planetary science at Caltech; Michiel Hogerheijde of the UC Berkeley department of astronomy; Mark Gurwell of the Harvard-Smithsonian Center for Astrophysics, and Duane Muhleman, professor emeritus of planetary science at Caltech.

Robert Tindol

Caltech discovers genetic process for controlling plant characteristics

PASADENA-Caltech biologists have harnessed a gene communication network that controls the size and shape of a flowering land plant.

The discovery is a fundamental advancement in understanding the processes that make plants what they are. The knowledge could also lead to greater control over certain characteristics of plants such as fruit size and stem durability.

In the March 19 issue of the journal Science, Professor of Biology Elliot Meyerowitz and his colleagues explain how they have managed to control three genes found in the "shoot apical meristem." This structure is the source of all cells creating a plant's leaves, stems, and flowers, and is somewhat analogous to the stem cells in animals.

The shoot apical meristem-also known as SAM-begins as a portion of the seed comprising just a few hundred cells. Like stem cells, they are undifferentiated at first, but as the young organism develops, they diversify to create the cells that make up all the recognizable features. "These divide in highly specific patterns to make leaves and stems and flowers," says Meyerowitz, who specializes in the molecular biology of plants. "Everything you see above ground arises from these cells."

Working with the nondescript flowering plant known as Arabidopsis thaliana, the Meyerowitz team first cloned the genes that gave appearance to the plant. These genes, known as CLV1 and CLV3, turned out to reveal a communication network that the plant uses to make its various parts.

Meyerowitz and his team discovered that the Arabidopsis plant tends to grow differently when the genes are disrupted. For example, the normal plant is about six inches in height with a thin, fragile stem and a few white flowers at the top.

But when the genes are knocked out, the plant grows a much thicker stem and mutant flowers with extra organs of all types, especially stamens and carpels.

In effect, this means that the researchers are in control of the genetic mechanism that governs various characteristics of a plant. And since the effect is genetic, the mutated characteristics are passed along to future generations.

Meyerowitz says the discovery could be used to mutate certain plants of human benefit so that they would have more favorable traits. For example, wheat might be altered so that the stem would be stouter and more resistant to being blown over.

But many of these effects have been accomplished for centuries with selective breeding, he says.

"The difference between a cherry tomato and a big beefsteak tomato is just like the difference between a normal Arabidopsis plant and those mutant for CLV1 or CLV3," he says. "We're not sure if it's exactly the same gene because we haven't yet looked.

"So there are ways to make fruit bigger, for example, without understanding the process," he says. "But what we're trying to do is understand the process."

Also involved in the research are Jennifer Fletcher, a research fellow in biology at Caltech; Mark Running, a graduate of Caltech who is now at UC Berkeley; Rüdiger Simon of the Institut für Entwicklungsbiologie in Cologne, Germany; and Ulrike Brand, a grad student in Simon's lab.

Robert Tindol

Caltech Question of the Month: What do the laws of physics, and the Heisenberg uncertainty principle in particular, say about whether free will exists?

Submitted by Robert R. Belliveau.

Answered by John Preskill, professor of theoretical physics, Caltech.

This is a deep question and there is no simple answer. I am not a philosopher; nor can I speak for all physicists. I can only state my personal views.

The question of free will implicitly relates to the issue of consciousness. Free will usually means the ability of conscious beings to influence their own future behavior. Its existence would seem to imply that different physical laws govern conscious systems and inanimate systems. I know of no persuasive evidence to support this viewpoint, and so I am inclined to reject it. It seems likely to me that it is possible in principle to predict the behavior of a person in the same sense that we can predict the behavior of an electron; it is just tremendously more difficult in practice.

That said, I feel that it would be too facile to completely dismiss the concept of free will. As the questioner rightly indicates, the deterministic worldview spawned by Newtonian physics has been overturned by quantum mechanics. Even in the case of a simple electron, I can have "complete" knowledge of the state of the electron, and yet I am still unable to predict with certainty where the electron will be found the next time I record its position. So it is with the universe. Even if I knew "everything" that could possibly be known about the universe a moment after the Big Bang, I could not predict everything about today's universe; the details hinge upon the random outcomes of countless tosses of the quantum dice. And so it is with a person.

But randomness is certainly not the same thing as free will. The illusion of free will (if it is an illusion) is sufficiently pervasive that I cherish my own ability to make decisions, while I certainly would not value my "ability" to make random choices! Free will is more than a limitation on predictability; it is the notion that "effects" can be "caused" by conscious beings.

Some scientists hope that a deeper grasp of the concept of free will might emerge from a more complete understanding of quantum reality. An eloquent appraisal of these issues can be found in the recent book The Fabric of Reality by David Deutsch. It's not an easy book, but then it's not an easy question!


New electron states observed by Caltech physicists

PASADENA—Caltech physicists have succeeded in forcing electrons to flow in an unusual way never previously observed in nature or in the lab.

According to James Eisenstein, professor of physics, he and his collaborators have observed electrons that, when confined to a two-dimensional plane and subjected to an intense magnetic field, can apparently tell the difference between "north-south" and "east-west" directions in their otherwise featureless environment. As such, the electrons are in a state very different from that of conventional isotropic solids, liquids, and gases.

"Electrons do bizarre and wonderful things in a magnetic field," says Eisenstein, explaining that electrons are elementary particles that naturally repel each other unless forced together.

By trapping billions of electrons on a flat surface within a semiconductor crystal wafer—and thus limiting them to two dimensions—Eisenstein's team is able to study what the electrons do at temperatures close to absolute zero and in the presence of large perpendicular magnetic fields.

Research on exotic states of electrons is relatively new, but its theoretical history goes back to the 1930s, when Eugene Wigner speculated that electrons in certain circumstances could actually form a sort of crystallized solid. It turns out that forcing electrons to lie in a two-dimensional plane increases the chances for such exotic configurations.

"They cannot get out of one another's way into the third dimension, and this actually increases the likelihood of unusual 'correlated' phases," Eisenstein says. Adding a magnetic field has a similar effect by forcing the electrons to move in tiny circular orbits rather than running unimpeded across the plane.

One of the best examples of the strange behavior of two-dimensional electron systems is the fractional quantum Hall effect, for which three American scientists won the Nobel Prize in physics last year. Electrons in such a system are essentially a liquid, and since the quantum effects of the subatomic world become a factor at such scales, the entire group takes on some unusual electrical properties.

Eisenstein's new findings are very different than the fractional quantum Hall effect. Most importantly, his group has found that a current sent one way through the flat plane of electrons tends to encounter much greater resistance than an equal current sent at a perpendicular angle. Normally, one would expect all the electrons to more or less disperse evenly across the flat plane, which would mean the same resistance for a current flowing at varying angles.

Dramatically, this "anisotropy" only sets in when the temperature of the electrons is reduced to within one-tenth of one degree above absolute zero, the lowest temperature a system can attain.

Owing to the laws of quantum mechanics, the circular orbits of the electrons exist only at discrete energies, called Landau levels. For the fractional quantum Hall effect, all of the electrons are in the lowest such level. Eisenstein's new results appear when the higher energy levels are also populated with electrons. While it appears that a minimum of three levels must be occupied, Eisenstein has seen the effects in many higher Landau levels.

"This generic aspect makes the new findings all the more important," comments Eisenstein.

One scheme that might explain the new results is that the electrons are accumulated into long ribbons. Physically, the system would somewhat resemble lines of billiard balls lying in parallel rows on a pool table. If this is what is happening, the Coulomb repulsion of the electrons is overwhelmed within the ribbons so that the electrons can cram more closely together, while in the spaces between the ribbons the number of electrons is reduced.

"There's not a good theoretical understanding of what's going on," Eisenstein says. "Some think such a 'charge-density wave' is at the heart; others think a more appropriate analogy might be the liquid crystal displays in a digital watch."

Another interesting question that could have deep underpinnings is how and why the system "chooses" its particular alignments. The alignment could have to do with the crystal substrate in the wafer, but Eisenstein says this is not clear.

Eisenstein and his collaborators are proceeding with their work, and have recently published results in the January 11 issue of the journal Physical Review Letters.

Heavily involved in the work are Mike Lilly, a Caltech postdoctoral scholar; and Ken Cooper, a Caltech graduate student in physics. Loren Pfeiffer and Ken West—both of Bell Laboratories, Lucent Technologies in Murray Hill, New Jersey—contribute the essential high-purity semiconductor wafers used in the experiments.

Robert Tindol

Caltech Question of the Month: If a lightbulb were one light-year away, how many watts would it have to be for us the see it with the naked eye?

Submitted by R. Anderson of Pomona, California, and answered by Dr. George Djorgovski, Professor of Astronomy

Star brightness is measured on a magnitude scale. The higher the magnitude, the less bright the object is. For example, Jupiter shines at about -2.5 in the night sky. The dimmest naked-eye object that we can see in the night sky (assuming we are looking someplace where it is dark, i.e., not Los Angeles) is 6th magnitude. Therefore, for the light from a lightbulb one light-year away to be 6th magnitude when it reaches Earth, the bulb would have to emit 10^27 watts of power. That is a billion, billion, billion watts.

Meanwhile, the faintest objects we can see with the Hubble Space Telescope, or the 10-meter Keck Telescopes are a few billion times fainter than what an unaided human eye (with a good vision) can see. While even these telescopes would not allow us to see a regular lightbulb placed one light-year away, they could easily detect a lightbulb on the Moon.



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