Star-watchers team up telescopes for a sharper view

October 19, 2015


What some astronomers are hailing as a glimpse of optical astronomy’s future looks decidedly unimpressive: a set of four 40-centimeter telescopes–no bigger than serious amateurs might have–mounted on steel trusses in a field near the University of Cambridge. Conduits carry light from each telescope into a steel tunnel, insulated with a thick layer of earth. But last September, this modest setup achieved a first: combining the light of separate optical telescopes to create a single image. Some of employee security best spotting scope to review around place they live

cambridge telescope

The initial images from this apparatus, dubbed COAST, for Cambridge Optical Aperture Synthesis Telescope, appear this month in Astronomy and Astrophysics. They are the first ever to distinguish the partners of the binary Star system Capella, and they reveal what all the excitement is about: From a system that cost just $1.2 million, loose change compared to the $2 billion-plus price tag of the Hubble Space Telescope, the Cambridge group has achieved a resolution five times better than Hubble’s.

“COAST is opening a window in optical astronomy,” says Ken Johnston of the U.S. Naval Observatory in Washington, D.C., which is building a similar system of its own. At the resolutions such systems could ultimately deliver, this light-combining technology should have an impact on astronomy comparable to that of the microscope in biology, he says. “All of a sudden you’re seeing two or three orders of magnitude more detail than you could see before.”

The principle, known as imaging interferometry, is nothing new to radio astronomers, who have years of experience combining signals from separate telescopes. But merging optical signals is a far more demanding task. The Cambridge group’s success may help overcome the lingering skepticism of astronomers who remember results from the early days of radio astronomy that “turned out not to be particularly reproducible,” says jasper Wall of Britain’s Royal Greenwich Observatory. It has also encouraged the half dozen other groups trying to construct similar systems. “Whatever we can learn from them we don’t have to learn the hard way ourselves,” says Oskar von der Luhe of the European Southern Observatory (ESO).

European Southern Observatory’s Headquarters in Garching near Munich Germany

Driving the rush to optical interferometry is astronomers’ hunger for better resolving power. The largest telescopes, such as the recently completed Keck 10-meter telescopes on Mauna Kea, Hawaii, still show stars as little more than bright specks. Astronomers want to see details in the specks–starspotg, flares, and the planets that may accompany stars. “Absolutely the only way is to have much bigger telescopes,” says John Baldwin, leader of the COAST group. A telescope with a 100-meter mirror could do the job. But even if such an instrument were feasible, its performance would be limited by atmospheric distortion: “One of the problems about any kind of high-resolution imaging is that the information that’s coming through the atmosphere has been very badly scrambled,” says fellow COAST scientist Craig Mackay.

Radio astronomers, however, have developed ways to cope with these problems. The long wavelength of radio waves increases the size of the telescope needed to get a particular resolution, but also eases the path to a solution: precisely merging signals from telescopes separated by many kilometers. The resulting “interferometer” has the resolution of a single telescope with a diameter equaling the separation of the smaller linked telescopes.

The key to this strategy is aperture synthesis, invented by Cambridge radio astronomer Martin Ryle in the early 1950s. When the output of two receivers surveying a pattern of light or radio emissions is combined, it yields an interference pattern that indicates the strength of a single regular component of the pattern. Aperture synthesis builds a complete image by applying the mathematics of Fourier analysis to the output of pairs of receivers twirled through the sky into different orientations by the Earth’s rotation.

Ryle’s strategy worked well for radio interferometers with baselines of no more than a few kilometers. But when separations grew larger, differences in atmospheric conditions experienced by the separate radiotelescopes scrambled the relative timing of wavefronts arriving at different receivers–the so-called phase information, which is critical to forming images. In 1958, however, the British radio astronomer Roger Jennison of the Jodrell Bank Observatory discovered that some information can be recovered in the so-called closure phase the sum of the phase differences around any closed loop of three or more detectors. (By combining aperture synthesis and closure phase, radio astronomers now routinely synthesize images from telescopes thousands of kilometers apart (Science, 22 January 1993, p. 454).

Most optical astronomers, working at the much shorter wavelengths of visible light, have been leery of all this wizardry. As Johnston puts it, “They don’t believe it will work.” The tolerances needed for combining images at visible wavelengths seemed impossibly severe, and they worried that all the processing steps between raw data and final image could create unrealistic artifacts. Until now, optical interferometry has been restricted to systems that combine light from two telescopes to measure a star’s diameter or relative position–applications that don’t require making an image. But after several proof-of-principle experiments, in which Mackay, Baldwin, and their colleagues masked the light of a single telescope to form separate beams and studied the resulting interference pattern, the COAST group was ready to try weaving light from separate telescopes into an image. The feat required fast, efficient detectors and high-precision laser control: “It was quite a nightmare getting it all done,” says Mackay.

COAST’s four telescopes, set in a 60-meter Y pattern, send their light to detectors via a system of trolley-mounted mirrors. Controlled by lasers, the trolleys move to compensate for Earth’s rotation, ensuring that by the time the four beams are combined they have traveled exactly the same distance, to within a few wavelengths of light. The trolleys also oscillate at a distinctive frequency for each beam to give its light an identifying signature.

This motion has the effect of sliding each beam back and forth relative to the others, so that when the light is merged, the resulting bright and dark interference bands sweep back and forth over the intensity detectors at a different rate for each pair of telescopes. The software can then disentangle the separate interference bands from each pair, analyze them to eliminate atmospheric distortion, and merge them to generate the image.

According to Mackay, the hardest part is getting the beams to overlap exactly, then keeping them that way. On the scale of a few wavelengths of light, he says, “all the things we are using in fact are rather wobbly and jellylike.” But it all worked well enough for COAST to make the first images ever of the two distinct stars in the Capella star system, which are about 100 million kilometers apart–closer than Earth to the sun.

“This demonstration is extremely important to show that this [technique] will do what it’s supposed to do,” says Johnston, who with his colleagues is building the Navy Prototype Optical Interferometer near Flagstaff, Arizona, where a six-beam system will generate star images by the summer of 1997. It will be joined by an array of five 1-meter telescopes slated for construction at the Mount Wilson Observatory near Pasadena, California. Still larger systems are in the offing at ESO’s Very Large Telescope in Chile, whose four 8-meter telescopes will operate part-time as an interferometer, and at the Keck.

With COAST and its successors, optical astronomy will enter a new era, say proponents of the technique. “Only interferometers have the capability for imaging the surface of stars in any way comparable to what we routinely do for the sun,” says Hal McAlister of Georgia State University, who heads the Mount Wilson project. The technology may also “Offer a view of planets around other stars (Science, 2 February, p. 588).” If these planets are pretty warm … there may be a fair chance you can image them, says von der Luhe.

Some optical astronomers are more cautious. Says Charles Jenkins of the Royal Greenwich Observatory, “The question about interferometry has to be not whether it will work, but whether it can be made to work on an interesting number of objects, and that means making it work on much fainter stars.” Faint objects require larger telescopes to gather more light, but atmospheric effects can scramble the crucial phase information across a single large mirror.

Observatoire de haute-provence

Antoine Labeyrie of the Observatory of Haute-Provence near Nice, a pioneer of optical interferometry who is currently constructing a prototype for an array of 27 telescopes, has no such doubts. “Large multitelescope systems,” he says, “are the unavoidable evolutionary path in optical astronomy.”


October 19, 2015


Search for life

RELATED ARTICLE: Join the Search for Life

You too can join the search for life in space! The SETI@home project, which was set to kick off in April, will allow anyone with a home computer and an Internet connection to analyze data received from the SERENDIP project.

Those who wish to participate in the program will start by downloading special screensaver software from SETI@home’s Web site. Anytime a participant’s computer is on but not being used, the screensaver will kick in and process data sent from SERENDIP.

SETI@home volunteers will periodically download chunks of data from SERENDIP over the Internet. When the home computer has processed one chunk, the operator sends it back to SETI. SETI will then send another chunk of unprocessed data back to the SETI@home volunteer. SETI computers are programmed to track each chunk of data and to alert a participant if his or her computer found an alien communication.

“[The project] provides a way for the public to actually and truly participate in… answering one of the most profound questions of all time: Is humanity, as a technological civilization, alone in the universe?” said Charlene Anderson, associate director of The Planetary Society in California.

As CE went to press, more than 250,000 people had already signed up to take part in SETI@home. If you’re interested (and your parents say it is okay), you can get more information at SETI@home’s Web site:

RELATED ARTICLE: Gasbags and Jellyblimps

What Kinds of Life Could Survive on Other Planets?

How do scientists know what to look for when they search the skies for alien life? Actually, they don’t. That’s probably why they are using so many programs to search for such life.

Generally, scientists assume that in order to sustain life, a planet has to have conditions similar to those found on Earth–a breathable atmosphere, plenty of water, and a temperature range warm enough to sustain life.

However, some scientists think that forms of life could exist that contradict everything we now know about life. Life may be able to exist without water or food as we know it. Or it may be able to endure temperatures that we can’t imagine any living thing withstanding.

Imagine a creature able to live on the tiny, icy planet of Pluto, nearly 3 billion miles away from the sun, with an average temperature of -370 degrees Fahrenheit. Or one that could somehow withstand Jupiter’s strong gravity. Or even some beast that would be able to thrive despite Mercury’s average daily temperature of 333 degrees Fahrenheit.

Scientists at Children’s Universe Atlas teamed up with artists to imagine just what kind of life could survive on each of our solar system’s planets. For Mars, they imagined a waterseeker, which uses a long snout to search for pockets of ice under Mars’ surface. For Venus, they came up with the Oucher-Poucher, which continually hops from one foot to the other to avoid burning its feet on Venus’s hot surface.

The picture at right shows jellyblimps and swordtails, the kinds of creatures scientists say might be able to live on Jupiter. Because of Jupiter’s strong gravity, any creature living there would have to remain in the air for its entire life. Jellyblimps would use their giant gasbags to keep afloat. Swordtails would use the strong gravity and their pointed tails to blast through their prey, the jellyblimps.

If scientists ever find life on other planets, what do you think it will be like?


October 19, 2015

P2: Other Searches

SETI scientists are already searching the skies for intelligent life in many ways:

* Project Phoenix

Project phoenixRun by SETI in Mountain View, Calif., Project Phoenix performs targeted searches for the sounds of alien civilizations. Rather than scanning the whole sky, Project Phoenix scientists direct a radio telescope only at nearby, sunlike stars. In addition, Project Phoenix scientists set the telescope to search out radio and TV signals at frequencies they say are most likely to be used for communications. Because the stars that Project Phoenix targets are similar to the sun, scientists say, they are more likely than bigger or smaller stars to have planets (like Earth) in their systems that can support life.

Project Phoenix scientists started in 1995 using a 64-meter radio telescope in Australia and continue to move to sites around the world trying to pick up signals from its chosen targets. Project scientists are currently using the 305-meter Arecibo radio telescope in Puerto Rico.

* Project Beta:

Project BetaProject Beta (The Billion-channel Extra-Terrestrial Assay) takes an approach opposite that used in Project Phoenix. Beta leader Paul Horowitz of Harvard University and his team use a radio telescope at Harvard University to sweep the entire sky over the course of a year, instead of aiming at specific targets. The team listens for a specific frequency that it believes would be used by aliens trying to be noticed.

Another project called META II is similar to BETA. In the South American country of Argentina, the Argentine Institute scans the skies in the Southern Hemisphere. (If you were looking at a globe, the Southern Hemisphere would be the half of the world south of the equator.)


SERENDIP stands for Search for Extraterrestrial Radio Emissions from Nearby Developed Intelligent Populations.

Often, SETI has to rent time on radio telescopes from astronomers using the telescopes for other purposes. The SERENDIP project finds time by “piggy-backing” on other organizations’ telescopes. At the same time as an organization is using its dish for other astronomy purposes, SERENDIP scientists can use the dish to listen for signals from space. SERENDIP’s work does not interfere with an organization’s radio astronomy work. The only downside to the project is that SERENDIP scientists cannot choose where to aim the telescope, but must just tag along on wherever the owner of the dish chooses.

Southern SERENDIP is a copy of the SERENDIP program that uses a radio telescope in Australia.

SERENDIP scientists have been very successful at collecting noise from space. In fact, they’ve been almost too successful. SERENDIP has accumulated so much data that SETI computers cannot process it all. That is why David Geyde and Dan Wertheimer came up with the idea of SETI@home, a program that will allow volunteers all over the world to download a special software program and noise data into their personal computers. The volunteers’ computers will analyze the data, and the volunteers will send the data back to SERENDIP. (See “Join the Search for Life” at right.)

What Have They Heard?

So with all of their efforts, what have scientists at SETI heard so far? Well, they haven’t heard anything–yet.

However, SETI scientists point out, the universe is so vast that there is still plenty of space that they have not yet been able to listen in on. The first contact with another life-form may not come for another 50 years, say SETI scientists. Or they emphasize, it could happen tomorrow.

“It’s a shot in the dark,” said Jack Welsh, a SETI expert and professor at the University of California-Berkeley.

Simply Not Talking?

What if there is life on other planets that simply does not communicate by radio signals? Perhaps such space aliens are no more than simple-celled creatures or fishlike creatures floating in strange seas. Perhaps they are birdlike animals soaring through unearthly skies.

Scientists are searching for such kinds of life also. NASA currently has two spacecraft exploring Mars, and two more are scheduled to land on Mars this year. (See CE 23.) Much of their work is focused on testing Martian soil for signs of life, or signs that some form of life may have once existed on Mars.

Last year, NASA sent the Cassini space probe toward Saturn to investigate the ringed planet and one of its moons, Titan. Cassini is expected to reach Saturn’s system around July 2004 and drop a probe called Huygens onto Titan’s surface. Titan is the only known moon in our solar system with a substantial atmosphere, and it may be able to support life. Huygens is programmed to test for life in the moon’s frigid oceans.

Though current missions to Mars and Titan are expected to radio information back to Earth, the Stardust spacecraft launched in February should actually collect matter and return it to Earth for analysis. Stardust is scheduled to cross within 93 miles of Comet Wild-2 in 2004.

Once near the comet, Stardust is programmed to collect just a fraction of an ounce of space dust from the comet and bring it back to Earth. Though scientists do not believe Comet Wild-2 has any life on it, they do believe that it may provide answers to how life might have begun on Earth. Some current theories contend the building blocks of life may have been deposited on Earth by comets crashing into the early Earth’s surface long ago.

There are some who believe that alien life continues to visit us here on Earth. Each year, there are numerous reports of sightings of spaceships and contacts with mysterious beings. Though it is easy to see why people are intrigued by such stories, there is no substantial scientific evidence that alien beings have ever set foot on Earth.

To find alien life, NASA, SETI, or someone else altogether will probably have to keep searching the stars. Scientists can only guess at what they will find. (See “Gasbags and Jellyblimps” below.) But unless we keep looking, scientists say, we will never know.

And so the search continues.


October 19, 2015


Radio Telescopes and Missions to Space Search the Heavens for Signs of Life and Alien Civilizations Radio Telescopes

The SETI Institute uses radio telescopes like the one illustrated here to search the skies for signs of intelligent life. Scientists at SETI hope that such devices will allow them to pick up signals from faraway civilizations.

Are we alone in the universe? Or do other beings, other civilizations, exist somewhere in the vastness of space? Those are questions that humans have puzzled over since our first ancestors looked with wonder into the night sky.

Giant Triangles and Mirrors

Throughout history, humans have thought of ways to communicate with space aliens.

* In 1820, German mathematician Carl Friedrich Gauss proposed carving a large right triangle in the Siberian forest so any aliens passing by the planet could see the symbol and recognize that intelligent life exists on Earth.

* In 1840, Austrian astronomer Joseph Von Littrow thought a group of giant flaming ditches in the Sahara would be the best way of getting the attention of possible extraterrestrials.

* In the 1860s, French inventor Charles Cros proposed building seven giant mirrors to reflect the sun’s light toward Mars. The mirrors, Cros said, should be shaped like the Big Dipper constellation to let any Martians who might be looking at Earth know that they are not alone.


Today, scientists are doing more than just proposing the building of giant mirrors or the digging of huge ditches. They are spending millions of dollars in a worldwide, high-tech search for signs of life beyond Earth.

Throughout the 1990s, scientists at the SETI (Search for Extra Terrestrial Intelligence) Institute in Berkeley, Calif., have been working to find any signs of other intelligent civilizations. SETI listens for signals from outer space through radio telescopes–telescopes that act much like giant ears, listening for the sounds generated by the universe.

Humans have been broadcasting radio and television signals for more than 60 years. Those signals don’t travel from place to place only on Earth; they go out into space as well. SETI scientists say that if alien civilizations exist, they might have developed radio and television technology, and they could be broadcasting signals of their own. Aliens might even have received and be responding to our TV and radio signals.

One of the most exciting projects at SETI is the building of its own giant radio telescope, called the One Hectare Telescope, or lhT. Rather than consisting of just one large telescope dish, the 1hT will be made up of between 500 and 1,000 small antennas, similar to backyard TV satellite dishes, spread over 1 hectare (about 100,000 square feet) of land. At that size, the lht will be many times larger than the Arecibo (Puerto Rico) telescope (a single dish telescope), currently the largest in the world.

The 1hT will also be more powerful than the Arecibo telescope. When completed in 2004, the 1hT “will have unique capabilities for observing objects from the solar system to the edge of the universe,” said Leo Blitz, director of the University of California-Berkeley Radio Lab. Because the lht will belong to SETI, scientists will be able to search space 24 hours a day, 365 days year.

Far-out jobs

October 19, 2015


NASA needs your help! The U.S. space agency wants to discover new worlds, like the ones you read about in “Alien Planets.” It needs people to fill five positions. Read the following job descriptions, and answer the questions below.

nasa blue marble


Would you love to see galaxies far, far away? Astrophysicists are astronomers who study stars, planets, and other objects in the universe. They determine how those objects were formed and what they are made of. Astrophysicists use special instruments, such as telescopes, to make observations.


Are you fascinated by the idea that there might be aliens on other planets? Astrobiologists explore the possibility of rife elsewhere in the universe. They also study rife on Earth to understand how we got here and what the future holds. Astrobiologists often conduct experiments using plants and animals.

Aerospace Engineer

Are you the kind of person who can make an awesome paper airplane? Is your model airplane seriously high-tech? Aerospace engineers design, build, and test spacecraft. Engineers determine what a spacecraft needs to be able to do, and then they try to create something that can handle that mission.


When you go hiking, are you fascinated by the different rock formations you see? Astrogeotogists try to determine the composition of planets. For example, they might analyze the surface of a planet to see whether it is made up of rock and contains water.


3, 2, 1 … blast off! Astronauts are trained to travel on space missions. Pilots are in charge of flight control. Mission specialists organize the missions. Payload specialists conduct experiments during the missions.

  1. You need to determine whether a newly discovered planet is composed mainly of gas like Neptune or of rock like Earth. You are an–.
  2. You are using data from the Kepler space telescope to try to locate Earth’s twin revolving around a distant star. You are an
  3. You heard that 54 planets can possibly sustain rife. Now you need to determine what kinds of organisms, if any, might be on those planets. You are an
  4. What does it take to become an aerospace engineer? Using the Internet, find out what kind of education and skirls are necessary for the job. Summarize your findings on a separate piece of paper.
  5. Go to NASA’s astronaut Web site at Choose one astronaut to read about. What is his or her space flight experience? Summarize it on a separate piece of paper.