In the footsteps of Galileo

Modern astronomy in Florence

Richard Demers
November 5, 2009

In addition to being one of the world's most well known centers of art, antiquity and crafts, Florence is a scientific and technological center of excellence. The Osservatorio Astrofisico di Arcetri (OAA) is the Florence branch of the Istituto Nazionale di Astrofisica (INAF; www.inaf.it). INAF, Italy's national institute of astrophysics, headquartered in Rome, is the government-funded entity charged with conducting astronomy and astrophysics research. At INAF Florence, known as Arcetri, about 170 astronomers, physicists, students, and international visitors are conducting research in areas such as the evolution of the early universe, star formation, solar physics, dark matter, supernovae, cosmic rays and adaptive optics.

 

During 2009, declared the Year of Astronomy by UNESCO and the International Astronomical Union, the astronomy community has been offering the public much more information and many, many exhibits and events focused on historical and modern astronomy. Florence in particular has been an epicenter of activity. As part of the public outreach effort, the Arcetri Observatory has organized several events designed to remind Florentines of their scientific and astronomical heritage (http://www.arcetri.astro.it/iya09/index.html).

 

At the center of this heritage is Galileo Galilei. Galileo carried out his astronomical observations during the winter of 1609-1610 while he was professor of mathematics at Padua University. Among his significant contributions to astronomy were the discovery of the four innermost moons of Jupiter (Io, Europa, Ganymede and Callisto) and the mapping of the phases of the earth's moon. Following these discoveries, at the invitation of the Medici's in 1610, he moved to Florence to assume a tenured position with the title Mathematician and Philosopher of the Grand Duke of Tuscany.

 

Indeed, the year 2009 was chosen as the Year of Astronomy in part because it marks the 400th anniversary of the invention of Galileo's telescope. His telescopes, one of which is on display at the Museo di Storia della Scienza, were revolutionary instruments in his time. But they are crude by today's standards. Because the camera did not yet exist, all of Galileo's observations and measurements were recorded by hand in his notebook, which includes his elaborate and beautiful sketches. To demonstrate the difficulty of Galileo's measurements and the extent of his skill, an Arcetri astronomer recently built a replica of Galileo's telescope using modern materials. The Arcetri astronomer then reproduced Galileo's observations of the phases of the moon using the replica telescope and a CCD camera to record the images. A side-by-side comparison of Galileo's original sketches of the moon and the recent images taken using the Galilean replica telescope will soon appear on the Arcetri website.

 

The conflict between Galileo and the Church has its origin in his defense of the heliocentric theory of the solar system, which some members of the clergy held was in direct conflict with scripture. The conflict culminated in his trial in Rome in 1633 on suspicion of heresy. His initially severe sentence was commuted to house arrest in his villa at Arcetri for the rest of his life. This villa, named Gioiello, is owned by the Italian government and administered by the University of Florence in association with the Arcetri Observatory, and it is a short walk from the summit of the Observatory to the door of Gioiello in the Pian de' Giullari quarter.

It was here that Galileo spent the last years of his life in seclusion when he wrote Two New Sciences, a treatise on kinematics and strength of materials which was later praised by Isaac Newton and Albert Einstein. The restoration of Gioiello was recently completed, and the villa is serene and deeply inspiring. A tower at the rear offers a breathtaking view of the Arcetri hillside that is characteristic of Tuscany. From the tower one can see the convent where Galileo's daughter, Sister Maria Celeste, lived until her death in 1634. She visited and cared for her father during his house arrest as his health was declining.

 

 

The accuracy and process for mapping the night sky and the scientific understanding of the universe have advanced enormously from the time of Galileo's observations thanks in part to the advancement of instruments such as the telescope. The Arcetri Observatory is contributing in this area in one of INAFs largest and most sophisticated projects. A group of scientists and engineers at Arcetri are in the final phase of acceptance testing a pair of adaptive optics (AO) systems that will be delivered to the Large Binocular Telescope on Mt. Graham, Arizona. As the adjective binocular implies, the observatory on Mt. Graham consists of a pair of identical twin telescopes, hence the need for a pair of AO systems from Arcetri. Each AO system-consisting of a one-meter secondary mirror, a glass pyramid wave front sensor and a control system-is designed to compensate for the atmospheric turbulence that distorts the starlight that astronomers wish to observe. The AO system accomplishes this by changing the shape or figure of the secondary mirror with a frequency of a thousand times per second, adapting itself to the atmospheric conditions in real time. The wave front sensor takes the measure of the atmospheric turbulence and the control system subsequently sends a command to the secondary mirror to correct for the measured turbulence.

 

Space telescopes such as the recently repaired Hubble Space Telescope do not suffer from atmospheric distortion, and as a result have clearer images. However, the cost of building and flying a space telescope is at about 20 times greater than the cost of building a terrestrial telescope with similar capability. The technology for removing atmospheric distortions in terrestrial telescopes enables astronomers to study fainter stars and more distant galaxies at far lower cost. The Large Binocular Telescope equipped with the Arcetri AO system holds the potential to discover habitable earth-like planets beyond our solar system. It will also help to answer the question of how the universe evolved from the uniform distribution of mass in the big bang to the lumpy distribution of galaxies, stars and planets currently observed.

 

The Arcetri AO group is now carrying out tests to measure the performance of their two AO systems. To facilitate these tests the group has modified a solar tower originally built to observe the sun. The solar tower has been reconfigured such that when the AO system is mounted in the tower, the group will be able to simulate its operation as if it were installed in the binocular telescope on Mt. Graham, its ultimate destination. Once the performance of the AO system is acceptable in the solar tower, it will make the long journey from Florence to Mt. Graham, Arizona.

 

The first light for the AO system on the Large Binocular Telescope on Mt. Graham, Arizona is expected to occur sometime in 2010. It will be an important event both for the AO group at Arcetri and for the astronomical community. When it is commissioned, it will be one of the largest collecting area terrestrial telescopes with AO correction. If it performs well, it will provide further validation for the implementation of even larger terrestrial telescopes with AO systems. In addition, it will enable a new phase of discoveries in astronomy and astrophysics.

 

Year of Astronomy events in Tuscany

Pianeta Galileo runs until November 20 and includes conferences, theatre, concerts and films highlighting Tuscany's role in the sciences-past and present. For information and a schedule of events, email pianetagalileo@consiglio.regione.toscana.it or call toll-free 800 40 12 91.

 

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