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Cesium-based clocks , one kind of atomic clock, measure the passage of time much more precisely than those based on the rotation of our planet, so adding a leap second allows astronomical time to catch up to atomic time. It's something time scientists have done since , when the first leap second was instituted. In fact, researchers inserted 10 extra seconds into the world's clocks because astronomical time and atomic time were off by so much. However, there are some time experts who argue against having a leap second, partly because of all the headaches they create every time they're added.
Most of us won't notice the addition, which happens at coordinated universal time UTC , or p. ET, unless we deal in timescales shorter than a second, or if we use a computer program that crashes because it can't handle the leap second. Leap seconds occur irregularly, which makes it hard for programmers to test their fixes, he explains.
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Leap seconds don't come on a regular schedule because Earth's rotation varies, says Demetrios Matsakis, chief scientist for time services with the United States Naval Observatory in Washington D. Our planet is slowing down , but it does so in unpredictable ways. So some periods require more leap seconds than others. The ITU makes the ultimate decision on whether to add a leap second or not. The last leap second was added in , but in the early s, time scientists were adding them every year, Levine explains.
Time: From Earth Rotation to Atomic Physics : Dennis D. McCarthy :
Levine is responsible for making sure the nation's timekeepers at NIST can handle the leap second. Even if all goes well during the addition, Levine and his team are usually greeted the morning after by a deluge of emails concerning various problems. Not everyone recognizes the leap second, although Apple does so on its devices. Google mobile devices sync with internet time services that are usually tied to atomic clocks.
The book presents homogenous and fluent discussions of the key problems, rendering a portrayal of recent advances in the field together with some basic concepts and essential infrastructure in orbital mechanics. The text contains introductory material followed by a gradual development of ideas interweaved to yield a coherent presentation of advanced topics.
Fundamental Astronomy: Edition 5. Hannu Karttunen. Fundamental Astronomy gives a well-balanced and comprehensive introduction to the topics of classical and modern astronomy. While emphasizing both the astronomical concepts and the underlying physical principles, the text provides a sound basis for more profound studies in the astronomical sciences.
The fifth edition of this successful undergraduate textbook has been extensively modernized and extended in the parts dealing with the Milky Way, extragalactic astronomy and cosmology as well as with extrasolar planets and the solar system as a consequence of recent results from satellite missions and the new definition by the International Astronomical Union of planets, dwarf planets and small solar-system bodies.
Furthermore a new chapter on astrobiology has been added. Kenneth Seidelmann. Theodore Gray.
Time: From Earth Rotation to Atomic Physics
With more than 1 million copies sold worldwide, The Elements is the most entertaining, comprehensive, and visually arresting book on all elements in the periodic table. Based on seven years of research and photography by Theodore Gray and Nick Mann, The Elements presents the most complete and visually arresting representation available to the naked eye of every atom in the universe. Organized sequentially by atomic number, every element is represented by a big beautiful photograph that most closely represents it in its purest form.
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The Hipparcos Satellite has concluded its observations, and the catalog is in preparation. Preliminary results assure that the Hipparcos catalog will provide positions, parallaxes and annual proper motions for over , stars with accuracies of 1. Hardcover , pages. More Details Original Title. Other Editions 3.
Time From Earth Rotation to Atomic Physics by Dennis D. McCarthy 9781107197282
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