Time In Astronomy Research Articles

Legacy Survey of Space and Time cadence strategy evaluations for active galactic nucleus time-series data in Wide-Fast-Deep field

ABSTRACT Machine learning is a promising tool to reconstruct time-series phenomena, such as variability of active galactic nuclei (AGNs), from sparsely sampled data. Here, we use three Continuous Autoregressive Moving Average (CARMA) representations of AGN variability – the Damped Random Walk (DRW) and (over/under)Damped Harmonic Oscillator – to simulate 10-yr AGN light curves as they would appear in the upcoming Vera Rubin Observatory Legacy Survey of Space and Time (LSST), and provide a public tool to generate these for any survey cadence. We investigate the impact on AGN science of five proposed cadence strategies for LSST’s primary Wide-Fast-Deep (WFD) survey. We apply for the first time in astronomy a novel Stochastic Recurrent Neural Network (SRNN) algorithm to reconstruct input light curves from the simulated LSST data, and provide a metric to evaluate how well SRNN can help recover the underlying CARMA parameters. We find that the light-curve reconstruction is most sensitive to the duration of gaps between observing season, and that of the proposed cadences, those that change the balance between filters, or avoid having long gaps in the g band perform better. Overall, SRNN is a promising means to reconstruct densely sampled AGN light curves and recover the long-term structure function of the DRW process (SF∞) reasonably well. However, we find that for all cadences, CARMA/SRNN models struggle to recover the decorrelation time-scale (τ) due to the long gaps in survey observations. This may indicate a major limitation in using LSST WFD data for AGN variability science.

New books & media

New books & media

Book Review: An American of Many Lives: Two Brides for Apollo: The Life of Samuel Williams, 1743–1817

AN AMERICAN OF MANY LIVES Two Brides for Apollo: The Life of Samuel Williams, 1743-1817. Robert Friend Rothschild (Universe, Inc., New York, 2009). Pp. xxx + 469. $29.95 (paperback). ISBN 978-0-595-51093-1.Samuel Williams (1743-1817) was a man of many lives: minister, astronomer, professor, journalist, naturalist, and historian. The first half of his life was lived in eastern Massachusetts in what passed for cosmopolitan surroundings in eighteenth-century New England; the second half was lived on the frontier in Vermont as a fugitive from justice. Robert Rothschild's well-written biography of Samuel Williams carefully lays out these successive careers and notes the interconnectedness of his life with that of political and religious events of the period.Williams was born in 1743 in rural Waltham, Massachusetts, the son of a Congregationalist minister and member of a distinguished Puritan family with roots back to 1638 in the colony. He was but one generation removed from the bloody Deerfield raid of 1704 in which Native Americans allied with the French murdered or captured members of his father's family. His grandfather, the Rev. John Williams, survived and wrote The redeemed captive returned to Zion (1707). Samuel Williams's own childhood was marked by peace, and he entered Harvard College in 1757. Like every Harvard student, he attended the prescribed lectures of John Winthrop, the Hollis Professor of Mathematics and Natural Philosophy. But he must have had a spark that caught Winthrop's eye, since the professor in 1 76 1 took Williams up to Newfoundland as one of his two student assistants to observe the transit of Venus. This astronomical expedition was a formative experience. When Williams returned home to prepare for the ministry, he continued his own observations with a 4-ft reflecting telescope and clock. The scientific highpoints of his later career were all related to astronomy.In 1765 Williams was elected minister of the Congregational church in Bradford, Massachusetts. He made time for astronomy between sermonizing, observing in 1769 a second transit of Venus from Newburyport. After fifteen years in Bradford, Williams was called back to Cambridge in 1780 to succeed John Winthrop as the Hollis Professor. At Harvard, Williams continued the general course of experimental lectures on scientific topics, but also expanded the curriculum with the addition of specialized courses - one on astronomy and another on comets. In 1780, he led a Harvard expedition to see a total eclipse of the Sun from Penboscot Bay, Maine (recording the phenomenon of Baily's beads fifty-six years before Baily), and in 1786, at the request of the General Court of Massachusetts, he undertook a geodetical survey of the Commonwealth's disputed border with New York. …

The Astronomer's Telegram: A Web‐based Short‐Notice Publication System for the Professional Astronomical Community

ABSTRACTThe Astronomer's Telegram (ATEL) is a web‐based short‐notice (<4000 characters) publication system for reporting and commenting on new astronomical observations, offering for the first time in astronomy effectively instantaneous distribution of time‐critical information for the entire professional community. It is designed to take advantage of the World Wide Web's simple user interface and the ability of computer programs to provide nearly all the necessary functions. This makes ATEL fast, efficient, and free. In practice, one may post a Telegram, which is instantly (<1 s) available at the web site and is distributed by e‐mail within 24 hours through the Daily Email Digest, which is tailored to the subject selections of each reader. In addition, authors reporting new outbursts of transients or coordinates of new objects (for example, gamma‐ray bursts or microlensing events) may request distribution by Instant Email Notices, which instantly (∼minutes) distributes their new Telegram by e‐mail to self‐identified workers interested in the same topic. This speed in distribution is obtained because no editing or reviewing is performed after posting—the last person to review the text before distribution is the author. Telegrams are enumerated chronologically, permanently archived, and referenceable. While ATEL will be of particular use to observers of transient objects (such as gamma‐ray bursts, microlenses, supernovae, novae, or X‐ray transients) or in fields that are rapidly evolving observationally, there are no restrictions on subject matter.

Ephemeris Time, relativity, and the problem of uniform time in astronomy

view Abstract Citations (12) References (10) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Ephemeris time, relativity, and the problem of uniform time in astronomy. Winkler, G. M. R. ; van Flandern, T. C. Abstract This paper contains a discussion of the difficult problems of time and its uniformity, with application to astronomy. The existing status of Ephemeris Time and Atomic Time is reviewed, and a view is given of the fundamental precepts governing useful time scales. Those relativistic concepts are discussed which are required for a thorough understanding of time processes, including the theoretical and practical differences between coordinate time and proper time. Finally, the IAU resolutions dealing with Ephemeris Time are described together with the background and motivations leading to a wish to replace it by a 'dynamical' time scale. Publication: The Astronomical Journal Pub Date: January 1977 DOI: 10.1086/112012 Bibcode: 1977AJ.....82...84W Keywords: Astronomy; Atomic Clocks; Ephemeris Time; Relativistic Effects; Time Measurement; Dynamic Response; Gravitation Theory; Light Speed; Relativity; Astrophysics full text sources ADS |

MEASURES OF TIME IN ASTRONOMY

ABSTRACT MEASURES OF TIME IN ASTRONOMY* J. DERRAL MULHOLLAND McDonald Observatory and Department of Astronomy, University of Texas at Austin Received 21 February 1972 "Time travels in divers paces... W. Shakespeare, A8 You Like It "The current definition of ephemeris time is philosophically repugnant, aesthetically , and completely inadequate." I.I. Shapiro, IAU Colloquium 9, 1970 August 'The time of an event given in the old scale, before the leap second, will be given as a date in the previous month, exceeding 24 hours ff necessary. The time of an event given in the scale after the step will be given as a date in the new month, with a negative time ff necessary. Trans. IAU, vol. 14B, p. 198 'The time is out ofjoint; 0 cursed spite, that ever I was born..." W. Shakespeare, Hamlet The prolfferation of time scales available to or known to the working astronomer has proceeded to the point that potentially harmful conflisions are widespread. The situation has been somewhat exacerbated by the major change recently effected in the time scale broadcast by WWV and similar services. A discussion is presented which attempts to the conceptual bases of time measures such as universal time and ephemeris time and ways in which the concepts are related to the actual determination of time. Areas of utility and obsolescence are indicated for the various kinds of clock time. Common measures of time not subject to clock-keeping are also described. Key words: time - year

BOOK AND FILM REVIEWS: Useful—But not Rigorous: Time in Astronomy

BOOK AND FILM REVIEWS: Useful—But not Rigorous: Time in Astronomy

Comparison System for Microscope Images

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