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Hyper-accurate clocks - the beating heart of Galileo
May 11, 2007Travellers have relied on accurate timekeeping for navigation since the development of the marine chronometer in the eighteenth century. Galileo, Europe's twenty-first century navigation system, also relies on clocks - but they are millions of times more accurate than those earlier timepieces.
The operational Galileo satellites will carry two types of clocks - passive hydrogen masers and rubidium atomic frequency standards. Each satellite will be equipped with two hydrogen masers, one of which will be the primary reference for generating the navigation signals, with the other as a cold (non-operating) spare.
Every operational satellite will also carry two rubidium clocks, one of which will be a hot (permanently running) backup for the operational hydrogen maser, instantly taking over should the maser fail and allowing signal generation to continue uninterrupted. The second rubidium clock will act as a cold spare.
GIOVE-A, the Galileo in-orbit verification satellite that is currently in service, carries two rubidium clocks - one operational and one cold spare. GIOVE-B, which is projected to enter service later this year, will carry one hydrogen maser and two rubidium clocks, one hot and one cold spare. The GIOVE-A2 satellite, which will be ready for launch in the second half of 2008, will carry a similar timekeeping payload to GIOVE-A, but will transmit additional navigation signals.
The Galileo passive hydrogen masers will keep time with an accuracy of around one nanosecond (one one-thousand-millionth of a second) in 24 hours - equivalent to losing or gaining a second in 2.7 million years. The rubidium clocks are accurate to 10 nanoseconds per day. In comparison, an ordinary digital wristwatch has an accuracy of about one second per day.
Galileo's passive hydrogen maser clocks will be around one thousand million times more accurate than a digital wristwatch.
The need for accuracy
Conceptually, Galileo users will determine their position by measuring how much time radio waves transmitted by satellites in the Galileo constellation take to reach them. Radio waves travel at about 300 million metres per second, so they cover a distance of around 0.3 metres in one nanosecond. In order to offer navigation accuracies of the order of a metre, Galileo time measurements must therefore be performed with a precision in the nanosecond range.
As a by-product of satellite navigation's need for accurate timekeeping, Galileo will also be able to offer precision time services to be used, for example, in the time stamping of financial transactions.
Galileo is a joint initiative between ESA and the European Commission. When fully deployed in the early years of the next decade, it will be the first civilian positioning system to offer global coverage.
European Space Agency
The need for accuracy
Conceptually, Galileo users will determine their position by measuring how much time radio waves transmitted by satellites in the Galileo constellation take to reach them. Radio waves travel at about 300 million metres per second, so they cover a distance of around 0.3 metres in one nanosecond. In order to offer navigation accuracies of the order of a metre, Galileo time measurements must therefore be performed with a precision in the nanosecond range.
As a by-product of satellite navigation's need for accurate timekeeping, Galileo will also be able to offer precision time services to be used, for example, in the time stamping of financial transactions.
Galileo is a joint initiative between ESA and the European Commission. When fully deployed in the early years of the next decade, it will be the first civilian positioning system to offer global coverage.
European Space Agency
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Galileo by Bertolt Brecht (Author), Eric Bentley (Editor), Eric Bentley (Editor), Charles Laughton (Editor) Considered by many to be one of Brecht's masterpieces, Galileo explores the question of a scientist's social and ethical responsibility, as the brilliant Galileo must choose between his life and his life's work when confronted with the demands of the Inquisition. Through the dramatic characterization of the famous physicist, Brecht examines the issues of scientific morality and the difficult relationship between the intellectual and authority. This version of the play is the famous one that was brought to completion by Brecht himself, working with Charles Laughton, who played Galileo in the first two American productions (Hollywood and New York, 1947). Since then the play has become a classic in the world repertoire. "The play which most strongly stamped on my mind a sense of Brecht's... |
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Dialogue Concerning the Two Chief World Systems (Modern Library Science) by Galileo (Author), Stillman Drake (Translator), John Heilbron (Translator), Albert Einstein (Translator) Galileo’s Dialogue Concerning the Two Chief World Systems, published in Florence in 1632, was the most proximate cause of his being brought to trial before the Inquisition. Using the dialogue form, a genre common in classical philosophical works, Galileo masterfully demonstrates the truth of the Copernican system over the Ptolemaic one, proving, for the first time, that the earth revolves around the sun. Its influence is incalculable. The Dialogue is not only one of the most important scientific treatises ever written, but a work of supreme clarity and accessibility, remaining as readable now as when it was first published. This edition uses the definitive text established by the University of California Press, in Stillman Drake’s translation, and includes a Foreword by Albert... |
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The Essential Galileo by Galileo Galilei (Author), Maurice A. Finocchiaro (Editor) Spanning Galileo's entire career, this new collection presents an annotated translation of Galileo's most important writings as judged by their historical impact from the seventeenth century to the present. It thus presents not only those writings that bear most closely on key developments in physics, astronomy, epistemology, and scientific methodology, but those most relevant to general culture as well, including writings on the relationship between science and religion. |
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Along Came Galileo by Jeanne Bendick (Author), Jeanne Bendick (Illustrator) One of the most important figures to come out of the awakening world of the Renaissance was Galileo Galelei. Often referred to as the "Archimedes of his time" Galileo was forever asking questions. Is it possible to measure heat? Is it possible to weigh air? Does the earth stand still or does it move? How fast do objects fall to the earth? His questions led to some of the most important answers of the scientific world and to his contributions to astronomy, physics, and mathematics. Galileo also advanced the astronomical telescope and invented the compound microscope. He measured the rotation of the sun, invented the thermometer, a geometrical compass and the pendulum clock. He was a man of faith, a lover of art and an accomplished artist. He played the lute and enjoyed working in his... |
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NOVA - Galileo's Battle for the Heavens Starring: Stacy Keach; Peter Thomas (VI); Don Wescott Directed By: Nova At a time when heretics were burned alive for dissent, scientist Galileo Galilei risked his life to advance his revolutionary concepts of the universe. British actor Simon Callow (Shakespeare in Love, Four Weddings and a Funeral) brings Galileo to life, humanizing the great thinker’s passion, intelligence, and arrogance while depicting his frustrations with fellow philosophers and scientists, and with Roman Catholic church leaders. Based on Dava Sobel’s best-selling biography Galileo’s Daughter, this two-hour film offers a vivid re-imagining of Galileo’s incredible achievements that forever changed the way we view our place in the universe. It also investigates the momentous personal and spiritual conflicts Galileo faced- most especially in defending the controversial... |
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Discoveries and Opinions of Galileo by Galileo Galilei (Author), Stillman Drake (Translator) Directing his polemics against the pedantry of his time, Galileo, as his own popularizer, addressed his writings to contemporary laymen. His support of Copernican cosmology, against the Church's strong opposition, his development of a telescope, and his unorthodox opinions as a philosopher of science were the central concerns of his career and the subjects of four of his most important writings. Drake's introductory essay place them in their biographical and historical context. |
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Chaney Instrument Galileo Thermometer with Glass Ball Barometer by Chaney Instruments This handsome unit uses a blend of old and new technology to interpret the weather. The Galileo thermometer is filled with a clear liquid that suspends multiple colored weights. As the liquid within the weights changes temperature their density changes allowing the weights to rise or fall. The lowest weight at the very top of the Galileo reflects the temperature. The glass water barometer indicates changes in the air temperature. A low fluid level in the glass spout generally means fair weather while a higher fluid level in the glass spout means foul weather approaches. |
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Galileo's Daughter: A Historical Memoir of Science, Faith, and Love by Dava Sobel (Author) Galileo Galilei's telescopes allowed him to discover a new reality in the heavens. But for publicly declaring his astounding argument--that the earth revolves around the sun--he was accused of heresy and put under house arrest by the Holy Office of the Inquisition. Living a far different life, Galileo's daughter Virginia, a cloistered nun, proved to be her father's greatest source of strength through the difficult years of his trial and persecution. Drawing upon the remarkable surviving letters that Virginia wrote to her father, Dava Sobel has written a fascinating history of Medici--era Italy, a mesmerizing account of Galileo's scientific discoveries and his trial by Church authorities, and a touching portrayal of a father--daughter relationship. Galileo's Daughter is a profoundly... |
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Galileo in Rome: The Rise and Fall of a Troublesome Genius by William R. Shea (Author), Mariano Artigas (Author) Galileo's trial by the Inquisition is one of the most dramatic incidents in the history of science and religion. Today, we tend to see this event in black and white--Galileo all white, the Church all black. Galileo in Rome presents a much more nuanced account of Galileo's relationship with Rome. The book offers a fascinating account of the six trips Galileo made to Rome, from his first visit at age 23, as an unemployed mathematician, to his final fateful journey to face the Inquisition. The authors reveal why the theory that the Earth revolves around the Sun, set forth in Galileo's Dialogue, stirred a hornet's nest of theological issues, and they argue that, despite these issues, the Church might have accepted Copernicus if there had been solid proof. More interesting, they show how... |
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Galileo FS-80/K-800 800 x 80mm Yoke Mount Reflector Telescope by Galileo Visions, Inc The Galileo FS-80 reflector telescope is a great beginner's reflecting telescope. The large 80mm primary mirror cell collects 33% more light than a 60mm refracting telescope. 1.25 focus housing permits the use of larger higher quality 1.25 eyepieces. Yoke mount makes the telescope easy to manage through altitude / azimuth (Up & Down, Left & Right) movement, and altitude slow motion control rod for precision adjustments. Galileo Trilogy software includes instructional videos and Planetarium program to help you pinpoint any star or planet at any given time. All of these features, along with all of the included accessories, ensure that you will have all you will ever need to observer the world around you just as Galileo did with your Galileo FS-80 refLEctor telescope. |
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