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The asteroid hunter who put Croatian astronomy on the map

25 February 2020

Korado Korlević heads a small observatory that plays a key role in tracking potentially hazardous near-Earth objects.

Višnjan Observatory at Tićan.
Višnjan Observatory is located in the picturesque village of Tićan, Croatia. Credit: Višnjan Observatory

When you visit Višnjan for the first time, it is hard to connect this quiet little town of barely 2000 residents on the Croatian peninsula of Istria with anything related to astronomy. It is even harder to imagine that a small, towerlike building standing in a lovely meadow in the nearby village of Tićan houses one of the most successful asteroid-hunting operations on Earth.

For the past two years, Višnjan Observatory has helped characterize about 40% of newly discovered near-Earth objects (NEOs), the population of mostly asteroids that approach within 1.3 astronomical units of the Sun. During that time it has participated in more NEO discoveries than all but two of the more than 500 institutions globally that share data with the International Astronomical Union’s Minor Planet Center (MPC). And the small Istrian observatory does so with a 1-meter optical telescope and an annual budget of no more than €10 000 (about $11 000).

Višnjan’s productivity is not a sudden development. Since the 1980s, observers there have discovered more than 1400 asteroids, most in the main belt between Mars and Jupiter, and have helped pin down the physical and orbital parameters of thousands of NEOs. It’s a task that has become even more crucial as NASA and other international groups strive to identify as many of the asteroids that present a potential hazard to Earth as possible.

At the heart of this low-budget success story is 61-year-old astronomer Korado Korlević. A teacher by training, Korlević doesn’t have a university degree in astronomy or physics. Yet he alone has discovered 1163 asteroids, which makes him, according to the MPC, the 21st most successful minor-planet hunter of all time.

In a country with one of the smallest budgets for research and innovation among all European Union nations (see the article by Mićo Tatalović and Nenad Jarić Dauenhauer, Physics Today, August 2019, page 30), Korlević is its most ardent promoter of science. Aside from putting Croatia on the map for astronomy, he hosts a popular science radio show, runs a science summer camp for children, and has helped train dozens of students to become world-class astronomers.

Becoming an NEO powerhouse

The story of Višnjan Observatory begins in the late 1970s, when Korlević and a couple of other young teachers from the local high school founded an amateur astronomy society. They figured that offering students a closer look at the stars would get them interested in science. “It was frustrating to watch these talented kids who had passion and motivation but were born in a rural area where expectations for their future were not too ambitious,” Korlević says. After managing to secure a building from the city council, the teachers purchased a small telescope. In the years that followed, the teachers and students built telescopes by hand.

By the early 1990s, Korlević had decided to focus the observatory’s efforts on detecting NEOs. It was a niche area of study with a low barrier to entry, and he was inspired by a research trip to the site of the 1908 Tunguska meteor explosion in Siberia. “I figured it was more useful to find the dangerous objects in advance than to research the impact sites,” Korlević says.

Korado Korlević.
Korado Korlević in 2011. Credit: Korado Korlević

During the Yugoslav Wars of the 1990s, the observatory gave up both its telescopes to the military. The bigger one ended up in Sarajevo, where it was used for surveillance of mortars during the Serbian siege of the city. Bosnian astronomer Muhamed Muminović personally returned the key components of the telescope after the war. The second telescope was lost after being used by the Croatian army in its war of independence, Korlević says.

Nevertheless, Korlević and his team of students and volunteers found ways to stay active during the war-torn decade. They built a specialized 40-centimeter reflecting telescope out of glass from a nearby factory and spare parts, including motors taken from an old dot-matrix printer. The electronics were assembled by high school students, and the software was written by university undergraduates.

During the 1990s, the observatory racked up more than 1000 main-belt asteroid discoveries, holding its own among well-funded facilities sporting far larger telescopes. “I think that period clearly demonstrates what is possible with a little talent and a can-do mentality,” says Mario Jurić, a University of Washington astronomer who at the time was a physics student at the University of Zagreb.

Students at the observatory.
Students perform much of the work at the observatory. Credit: Višnjan Observatory

Jurić helped bolster the facility’s efficiency by codeveloping the Višnjan Observatory Images Database. To search for new objects, the staff had previously had to manually compare the locations of all known asteroids with those of objects identified in new pictures of the sky. Jurić and a few other students made a local database of known asteroids and then applied software algorithms to predict the objects’ locations at the time of observations. When an image from the telescope appeared on the computer, all known objects were marked, enabling the staff to quickly focus on unflagged objects. The process sped up the detection procedure significantly. “It is standard today, but it was pretty unusual at the end of the ’90s, especially for the smaller observatories like Višnjan,” Jurić says. “And it was made by a bunch of kids.”

Today Jurić is one of the world’s leading experts in Big Data projects in astronomy. He heads the data management team for the Vera C. Rubin Observatory (formerly called the Large Synoptic Survey Telescope), a facility under construction that aims to conduct the largest sky survey ever.

Modern upgrades

At the beginning of the new millennium, Višnjan Observatory received a major upgrade: a 1-meter telescope named Dagor that had been designed in the 1980s by the Italian astrophysicist Margherita Hack. The telescope was located for some time in Basovizza, near the Italy–Slovenia border, before it was given to Višnjan Observatory in 2002.

The Višnjan crew placed Dagor in a new, slightly larger facility in the nearby village of Tićan and made improvements to tailor the telescope to their needs. “It is very specialized, like a motor for a motocross motorcycle,” Korlević says. With its large field of view and high-sensitivity CCD camera, Dagor specializes in observing fast-moving, small objects—not only asteroids and comets but also human-made entities like satellites and space trash.

Though Korlević and his colleagues continue to detect new asteroids, they have become increasingly focused on tracking NEOs that are first identified by other, larger facilities. Due to its location halfway around the world from large observing stations in the southwestern US and Hawaii, the Croatian observatory can spot objects within 10 to 12 hours of discovery, ensuring that they are monitored consistently to pin down their orbital characteristics.

“Višnjan Observatory is very efficient at providing astrometric measures, which allow us to refine the orbital calculations,” says Tim Spahr, the MPC director from 2007 to 2014. “It provides critical follow-up of objects.”

Almost every night, Korlević or one of the volunteers spends hours by Dagor. There is always a list of objects, which were spotted by larger observatories, that need to be tracked. They measure the objects’ position, movement, and brightness. Once all the orbital parameters are determined, the MPC makes the discovery official and publishes information about the object, along with a list of the observatories that contributed to its detection, in a database. The MPC data are then used by multiple institutions, including the European Space Agency’s Near-Earth Object Coordination Centre and NASA/JPL Center for NEO Studies, to evaluate the degree of risk posed by individual NEOs.

Korlević acknowledges that the geographical position of the observatory is one reason for its success, as is weather that is generally better than that at other European observatory sites. “But we also have some unusual methods,” he says.

Unlike many other asteroid hunters, Korlević often continues to conduct observations in poor weather. “It is harder to work with clouds, and nobody likes to have a wet instrument in the end,” he says. “But in half of these cases it is still possible to do a good job, especially if you are exactly aware of the limitations and how to deal with them.” He was also an early adopter of now-common techniques such as synthetic tracking, which involves taking a multitude of short-exposure pictures and then summing them to compensate for suboptimal viewing conditions.

The final, crucial ingredient for success is plain passion, Korlević says. Many students and other volunteers from Croatia and abroad are happy to help track NEOs during the night shift. “They get the sense of doing something important,” he says.

Educating astronomers

Over the years, numerous high school and college students have experienced asteroid hunting firsthand by visiting and volunteering in the observatory for a day or for weeks as participants in astronomy summer schools. “We are trying to educate the next generations who will do this job,” Korlević says.

Dagor telescope.
The 1-meter Dagor telescope at Višnjan Observatory tracks hundreds of NEOs annually. L01 is the observatory’s code with the Minor Planet Center. Credit: Višnjan Observatory

Consequently, there are dozens of successful Croatian scientists scattered around the world who say that their experiences in Višnjan strongly influenced their careers. Marina Rejkuba, an astronomer who heads the European Southern Observatory User Support Department, recalls visiting Višnjan Observatory in the early 1990s, when she was a physics student at the University of Zagreb. “A group of us went to visit Višnjan, and I remember that Korado asked us which projects we planned to carry out,” Rejkuba says. “Back then we didn’t have this research-oriented mind-set. That changed after our interaction with Korado. We got the possibility to do research and at the same time learn about observational astronomy.”

Rejkuba attended Višnjan summer school several years in a row and eventually became an assistant project leader. Through friends she made at Višnjan, she got in touch with an astronomer at Asiago Observatory at the University of Padua in Italy. She carried out her undergraduate thesis work there using professional telescopes, and she was hooked for life. “Meeting Korado and getting the first taste of astronomy research in Višnjan decided my career and future life,” Rejkuba says.

“Korado’s key contribution has been to give room and ample encouragement to a bunch of kids to test how far they can get with the talents and skills they have,” says the University of Washington’s Jurić, who discovered with Korlević 125 asteroids and one comet, now named 183P/Korlević–Jurić. He encourages them to aim high, to be creative in overcoming obstacles, and to improve their skills until they reach their goals. “It is a very entrepreneurial way of thinking, which in my experience is very rarely present in Central European education,” Jurić says.

Marina Rejkuba.
Marina Rejkuba, head of the European Southern Observatory User Support Department, speaks at a 2017 press conference announcing the discovery of a neutron-star merger. Rejkuba spent several summers during her university years at Višnjan Observatory. Credit: ESO/M. Zamani

Other Višnjan alumni express similar sentiments. Former students who acknowledge their experience as a major influence include Marina Brozović, a radar scientist at NASA’s Jet Propulsion Laboratory in Pasadena, California, who works on radar observations of NEOs; Silvija Gradečak, the leader of a materials science and engineering group at MIT; and Ana Bonaca, a researcher at the Harvard–Smithsonian Center for Astrophysics who studies galaxy dynamics and dark matter.

Promoting science

Although many Croatians recognize Korlević as an astronomer and a promoter of science—devoted fans listen every week to his radio show, Explora—perhaps his biggest influence on Croatian society comes through his efforts in education. Along with the observatory, the Višnjan area also hosts the Science and Education Centre, which for the past three decades has offered summer science camps that extend far beyond astronomy.

Summer program.
Students perform a chemistry experiment as part of a summer program in Višnjan. Credit: Korado Korlević

Each year as summer vacation begins, a Višnjan school building starts to fill with some 600 children and teenagers from all over Croatia and neighboring countries. A one-week program for elementary school pupils includes workshops and experiments in biology, astronomy, physics, chemistry, and robotics. In small laboratories, children figure out the ingredients in sunscreen, compare Neanderthal teeth and jaws with their own, and assemble simple robots. They observe the Moon through telescopes and then build telescopes of their own. Kindergartners explore nature during organized walks in the woods, where they learn why rain falls and how to recognize occupied animal burrows.

“They have to learn to always feel at home, no matter where they go,” Korlević says. “It’s a very important thing for future researchers.” The education center covers half the expenses, lowering the price to €200–250 per student for some programs.

Evening program at the observatory.
The Tićan dome at night. Credit: Višnjan Observatory

Interest in Višnjan’s science workshops has grown steadily. Today the summer programs quickly reach capacity without advertising. It helps that former participants like to return and voluntarily assist in the classroom. Last summer, the center drew more than 70 volunteers from Croatia, Italy, Slovenia, Bosnia and Herzegovina, Serbia, and even Canada.

Looking ahead

Recent global efforts to prioritize NEO detection mean that the tracking work of the Istrian observatory is more important than ever. An international group of organizations, including NASA and the European Space Agency, established the International Asteroid Warning Network in 2013 to detect, track, and characterize NEOs. NASA is working to satisfy a congressional mandate to identify at least 90% of the estimated population of NEOs that are larger than 140 meters in diameter. Korlević predicts that the number of discovered objects will rise with the rapid development of telescopes and satellites. “I think there is now serious awareness about asteroid danger and a focus on solving this problem—which is possible,” he says.

But the opportunity is accompanied by challenges. In recent years, light pollution, particularly from the LED illumination used in nearby cities and tourist sites, has affected telescope observations; each year, Korlević says, the observatory loses some sensitivity. Last year Croatia enacted a fairly strict law that sets limits on light pollution, but Korlević says it is not yet being enforced. A local citizen initiative demands an addition to the law that would implement a low-light area, measuring 25 kilometers in diameter, around the observatory.

In December Korlević received a grant of almost $11 000 to purchase new components for Dagor and to reapply an aluminum coating that was damaged by humidity. The improvements will be helpful, but to stay highly productive, Višnjan will need a new, more powerful telescope. Pessimistic about receiving financial help from governmental and nongovernmental institutions in Croatia, Korlević is ready to once again get his hands dirty: “We are going to build it ourselves.”

Beyond Višnjan

Astronomski Centar Rijeka.
Rijeka Astronomical Centre features a telescope dome, a digital planetarium, and a view of Kvarner Bay. Credit: Rijeka Astronomical Centre

Although no other domestic observatory can match the scientific importance of Višnjan, the 20 or so observatories in Croatia are becoming increasingly important for the popularization of science. “We don’t have astronomy within our formal elementary and high school educational system, so observatories offer possibilities for young people to get this kind of knowledge,” says Dragan Roša, the head of Zagreb Observatory, in the Croatian capital. Established in 1903, it is one of the country’s oldest such facilities. A few other institutions have a similarly long tradition, but many are recently established. Almost all of them are the result of persistent passion and enthusiasm from local amateur astronomy societies.

In the Croatian port city of Rijeka, an astronomy center established in 2001 was the fulfillment of more than three decades of lobbying by dozens of astronomy enthusiasts. The small observatory has a spectacular location high above the city, at the site of a World War II fortress. The terrace of a rooftop café offers a stunning view of the Adriatic Sea’s Kvarner Bay: The crystalline blue water is punctuated by a couple of islands to the south, and Učka mountain and its surrounding nature park rise steeply to the west. Some 2 kilometers away, on the adjacent hill of Trsat, another 20th-century military complex is being partially converted into a large campus for the University of Rijeka.

The spectacular views of Učka and the Adriatic are not the only attractions here. Rijeka Astronomical Centre hosts the country’s only digital planetarium, a lecture hall, and exhibition and workshop spaces decorated with children’s drawings of space. Families flock here for the educational programs, while teenagers and the elderly come to chill out, literally, as the evening breeze makes it one of the few tolerable locations in the city during the heat of high summer. An area once largely off-limits has been turned into a focal point for the local population, one that mixes leisure with science and education.

Each year around 10 000 visitors pass through the center, most of them schoolchildren, says Vanesa Ujčić Ožbolt of the Rijeka Academic Astronomical Society. The most popular activity for visitors of all ages, she says, is looking at the sky through the telescope.

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