Skip to main content Accessibility help

We use cookies to distinguish you from other users and to provide you with a better experience on our websites. Close this message to accept cookies or find out how to manage your cookie settings.

Close cookie message
×
  1. Home
  2. Browse subjects
  3. Physics and Astronomy
  4. Observational Astronomy, Techniques and Instrumentation
  5. Content Listing

Refine search

Refine search

Access:
Content type:
Publication date:
Apply   From and To filters
Subject: Show more
Journals Show more
Publishers: Show more
Societies Show more
Series: Show more
Collections: Show more

Actions for selected content:

Select all | Deselect all
  • View selected items
  • Export citations
  • Download PDF (zip)
  • Save to Kindle
  • Save to Dropbox
  • Save to Google Drive

Save Search

You can save your searches here and later view and run them again in "My saved searches".

Please provide a title, maximum of 40 characters.
Cancel
×

957 results in Observational Astronomy, Techniques and Instrumentation

Page 11 of 48

  • 12 - Optical Atomic Standards

  • Dennis D. McCarthy, United States Naval Observatory, P. Kenneth Seidelmann, University of Virginia
  • Book:
    Time: From Earth Rotation to Atomic Physics
    Published online:
    01 October 2018
    Print publication:
    18 October 2018, pp 203-214

  • Summary

    Higher atomic transition frequencies in the optical wavelength region provide the opportunity for improved precision in comparison with microwave frequencies. One application uses a single ion with long transition lifetimes when trapped by electric fields and laser cooled. Another method uses laser-cooled atoms confined in optical lattices. The International Committee for Weights and Measures has recommended optical frequency standards for secondary representation of the second, and a number of laboratories have developed optical ion clocks and optical lattice clocks using different ions. One challenge is comparing the clocks at different locations at the accuracy of the clocks. Also at the 10-18 level, the geoid of the Earth is not well defined.

  • 9 - Dynamical and Coordinate Timescales

  • Dennis D. McCarthy, United States Naval Observatory, P. Kenneth Seidelmann, University of Virginia
  • Book:
    Time: From Earth Rotation to Atomic Physics
    Published online:
    01 October 2018
    Print publication:
    18 October 2018, pp 131-147

  • Summary

    With the recognition of the problems with Ephemeris Time and the need to make changes in the celestial reference system in 1976, improved dynamical timescales continuous with Ephemeris Time and consistent with the theory of relativity were developed. Dynamical time is understood as the time-like argument of dynamical theories and the independent variable of the equations of motion of solar system bodies. In 1976, Terrestrial Dynamical Time (TDT) and Barycentric Dynamical Time (TDB) were introduced. Problems with the definition of TDT and TDB and the need for a new reference system based on accurate observations of distant radio sources were recognized. So Terrestrial Time (TT), Geocentric Coordinate Time (TCG), and Barycentric Coordinate Time (TCB) were introduced, and TDB was redefined. Barycentric Ephemeris Time (Teph) was officially recognized. Ephemeris Time Revised is still necessary for timescales prior to 1956. Relativistic equations specify the relationships between the different timescales.

  • 19 - International Activities

  • Dennis D. McCarthy, United States Naval Observatory, P. Kenneth Seidelmann, University of Virginia
  • Book:
    Time: From Earth Rotation to Atomic Physics
    Published online:
    01 October 2018
    Print publication:
    18 October 2018, pp 316-333

  • Summary

    Time is an international standard involving many national and international organizations that deal with the aspects of time and timekeeping. The treaty of the meter in 1875 established the Bureau International des poids et mesures (BIPM), whose activities now include time. The Conférence Générale des poids et mesures (CGPM) and the Comité international des poids et mesures (CIPM) were also established at that time. Scientific unions, such as the International Astronomical Union, the International Union of Geodesy and Geophysics, and the International Telecommunications Union, promote investigations of scientific and technical problems. Service organizations, such as the International Earth Rotation and Reference Systems Service, the International VLBI Service, International Laser Ranging Service, International GNSS Service , and International DORIS Service, deal with coordination and analysis of observations related to the Earth’s orientation.

  • 10 - Clock Developments

  • Dennis D. McCarthy, United States Naval Observatory, P. Kenneth Seidelmann, University of Virginia
  • Book:
    Time: From Earth Rotation to Atomic Physics
    Published online:
    01 October 2018
    Print publication:
    18 October 2018, pp 148-170

  • Summary

    The word "clock" comes from a medieval word for bell, and the original purpose of clocks was to ring bells. The division of the day into 24 hours by the ancient Egyptians created hours of different lengths depending on the season of the year. Early devices, designed to measure time intervals, were based on the flow of water, burning candles, incense sticks, and sand flow. Mechanical clocks appeared in the latter part of the 13th century, and the development of pendulum clocks originally conceived by Galileo led to significant improvements in timekeeping. Because of the difficulty in creating clocks marking seasonal hours, however, clocks were made to display equal hours. The pendulum clock went through many developments to achieve improved accuracies. Further improvements in clock technology included the development of chronometers for navigation at sea and quartz crystal clocks. These improvements can be quantified numerically by precision, accuracy, and stability.

  • 7 - Relativity and Time

  • Dennis D. McCarthy, United States Naval Observatory, P. Kenneth Seidelmann, University of Virginia
  • Book:
    Time: From Earth Rotation to Atomic Physics
    Published online:
    01 October 2018
    Print publication:
    18 October 2018, pp 104-122

  • Summary

    Although Albert Einstein had proposed the theory of special relativity in 1905, Newtonian reference systems continued to be adequate for most practical purposes into the 1960s. Space exploration, artificial Earth satellites, and more accurate timescales, however created the requirement to distinguish between proper and coordinate time, and to include relativistic effects, such as time dilation. A relativistic framework was necessary for time transfer and time transformations between coordinate times in the solar system. General relativity metrics and the equivalence principle were considered in the definitions of Barycentric and Geocentric Celestial Reference Systems, introduced by the IAU in 2000.

  • 5 - Earth Orientation

  • Dennis D. McCarthy, United States Naval Observatory, P. Kenneth Seidelmann, University of Virginia
  • Book:
    Time: From Earth Rotation to Atomic Physics
    Published online:
    01 October 2018
    Print publication:
    18 October 2018, pp 68-87

  • Summary

    The International Celestial Reference System (ICRS) provides the models, constants, and algorithms along with the International Celestial Reference Frame (ICRF) used to describe the positions and motions of celestial objects. Similarly, the International Terrestrial Reference System (ITRS) provides the models, constants, and algorithms along with the International Terrestrial Reference Frame (ICRF) used to describe the positions and motions of locations on the Earth. Algorithms that account for precession, nutation, variations in the Earth's rotational speed, and polar motion are available to transform coordinates and time between the two systems These rely on routine astronomical observations, but systematic changes in the systems and/or the transformation procedures can occur occasionally.

Time: From Earth Rotation to Atomic Physics
  • 2nd edition
  • Dennis D. McCarthy, P. Kenneth Seidelmann
  • Published online:
    01 October 2018
    Print publication:
    18 October 2018
  • In the twenty-first century, we take the means to measure time for granted, without contemplating the sophisticated concepts on which our time scales are based. This volume presents the evolution of concepts of time and methods of time keeping up to the present day. It outlines the progression of time based on sundials, water clocks, and the Earth's rotation, to time measurement using pendulum clocks, quartz crystal clocks, and atomic frequency standards. Time scales created as a result of these improvements in technology and the development of general and special relativity are explained. This second edition has been updated throughout to describe twentieth- and twenty-first-century advances and discusses the redefinition of SI units and the future of UTC. A new chapter on time and cosmology has been added. This broad-ranging reference benefits a diverse readership, including historians, scientists, engineers, educators, and it is accessible to general readers.

  • 2 - HTRA Instrumentation I

  • Edited by Tariq Shahbaz, Instituto de Astrofísica de Canarias, Tenerife, Jorge Casares Velázquez, Instituto de Astrofísica de Canarias, Tenerife, Teodoro Muñoz Darias, Instituto de Astrofísica de Canarias, Tenerife
  • Book:
    High Time-Resolution Astrophysics
    Published online:
    31 July 2018
    Print publication:
    02 August 2018, pp 43-66
    • Chapter
      • You have access
    • PDF
    • Export citation

  • Summary

    The range in wavelength and time-resolution of current instrumentation for carrying out astrophysical studies has increased dramatically over the last five decades. Here I will give a brief historical review of time-domain astronomy, followed by a summary of the facilities available now from X-ray to near-IR wavelengths. I will then give a glimpse of various remarkable technologies under development for the next generation of ground and space-based observatories which will take such studies to unprecedented levels.

  • 6 - Incorporating Gamma-ray Data into High-Time Resolution Astrophysics

  • Edited by Tariq Shahbaz, Instituto de Astrofísica de Canarias, Tenerife, Jorge Casares Velázquez, Instituto de Astrofísica de Canarias, Tenerife, Teodoro Muñoz Darias, Instituto de Astrofísica de Canarias, Tenerife
  • Book:
    High Time-Resolution Astrophysics
    Published online:
    31 July 2018
    Print publication:
    02 August 2018, pp 169-194

  • Summary

    At high energies, high time resolution data is limited by statistics, with gamma-ray instruments like {\it Fermi}-LAT detecting fewer than a single photon per day for the average source. However, the time of arrival for each high-energy photon is known very accurately. This means that high-energy data can still be useful for sources with timing signatures, such as pulsars or galactic binaries. With it's all-sky observing strategy, the LAT also provides monitoring for sources with gamma-ray signals associated with flares or state transitions. Transitional pulsars are a prime example of these sorts of systems, as transitions between their low-mass X-ray binary and rotation-powered states appear to correlate with an offset in overall gamma-ray flux. Here we discuss the {\it Fermi} mission and instruments, the wide variety of gamma-ray sources, and details of the maximum likelihood analysis method. We also describe some recommendations for using gamma-ray data when investigating sources with time signatures that are singificantly shorter than the time separating individual gamma-ray events.

  • 3 - HTRA Instrumentation II

  • Edited by Tariq Shahbaz, Instituto de Astrofísica de Canarias, Tenerife, Jorge Casares Velázquez, Instituto de Astrofísica de Canarias, Tenerife, Teodoro Muñoz Darias, Instituto de Astrofísica de Canarias, Tenerife
  • Book:
    High Time-Resolution Astrophysics
    Published online:
    31 July 2018
    Print publication:
    02 August 2018, pp 67-96

  • Summary

    This paper is based on the lectures I gave at the XXVII Canary Islands Winter School of Astrophysics on High Time-Resolution Astrophysics (HTRA). I provide a detailed description of three instruments that have been designed to study HTRA in the optical part of the spectrum: ULTRACAM, ULTRASPEC and HiPERCAM.

  • 1 - Radiation Processes and Models

  • Edited by Tariq Shahbaz, Instituto de Astrofísica de Canarias, Tenerife, Jorge Casares Velázquez, Instituto de Astrofísica de Canarias, Tenerife, Teodoro Muñoz Darias, Instituto de Astrofísica de Canarias, Tenerife
  • Book:
    High Time-Resolution Astrophysics
    Published online:
    31 July 2018
    Print publication:
    02 August 2018, pp 1-42

  • Summary

    This is a basic introduction to the physics of compact objects in the context of High Time Resolution Astrophysics (HTRA). The main mechanisms of energy release and the properties of relevant radiation processes are briefly reviewed. As a specific example, the top models for the multi-wavelength variability of accreting black holes are unveiled.}

Page 11 of 48