Re: computational amateur astronomy?
- From: Sam Wormley <swormley1@xxxxxxxxx>
- Date: Wed, 29 Jun 2005 21:32:11 GMT
Jonathan Bartlett wrote:
I've been thinking about getting started in amateur astronomy. However, I'm from the computer science area, and as such I love computing/calculation. I've been disappointed because most amateur astronomy books just focus on looking at things. I would also enjoy calculating things. Is it possible with amateur equipment to make any sort of meaningful calculations? Distances, speeds, anything? I imagine so, since Kepler and Newton probably had less equipment and was able to determine the laws of planetary motion. Anyway, I was curious if anyone knew of a good beginner book or website that shows how to re-make such classic calculations or do any other kind of computational astronomy.
Thanks!
Jon
ASTRONOMICAL ALGORITHMS by Jean Meeus Willmann-Bell, Inc., P.O. Box 35025, Richmond, Virginia 23235 1991 QB51.3.E43M42 1991 520-dc20 91-23501 CIP
In the Foreword, Roger W. Sinnott, of Sky & Telescope magazine writes, "People who write their own computer programs often wonder why the machine gives inaccurate planet positions, an unreal eclipse track, or a faulty Moon phase. Sometimes they insist, bewildered, 'and I used double precision, too.' Even commercial software is sometimes afflicted with gremlins, which comes as quite a shock to anyone caught up in the mystique and presumed infallibility of computers. Good techniques can help us avoid erroneous results from a flawed program or a simplistic procedure--and that's what this book is all about. "In the field of celestial calculations, Jean Meeus has enjoyed wide acclaim and respect since long before microcomputers and pocket calculators appeared on the market. When he brought out his ASTRONOMICAL FORMULAE FOR CALCULATORS in 1979, it was practically the only book of its genre. It quickly became the "source among sources," even for other writers in the field. Many of them have warmly acknowledged their debt (or should have), citing the unparalleled clarity of his instructions and the rigor of his methods.
"And now the Belgian astronomer has outdone himself yet again! Virtually every previous handbook on celestial calculations (including his own earlier work) was forced to rely on formulae for the Sun, Moon, and planets that were developed in the last century--or at least before 1920. The past 10 years, however, have seen a stunning revolution in how the world's major observatories produce their almanacs. The Jet Propulsion Laboratory in California and the U.S. Naval Observatory in Washington, D.C., have perfected powerful new machine methods for modeling the motions and interactions of bodies within the solar system. At the same time in Paris, the Bureau des Longitudes has been a beehive of activity aimed as describing these motions analytically, in the form of explicit equations.
"Yet until now the fruits of this exciting work have remained mostly out of reach of ordinary people. The details have existed mainly on reels of magnetic tape in a form comprehensible only to the largest brains, human or electronic. But ASTRONOMICAL ALGORITHMS changes all that. With his special knack for computations of all sorts, the author has made the essentials of these modern techniques available to us all.
_________________________________
EXPLANATORY SUPPLEMENT TO THE ASTRONOMICAL ALMANAC Edited by P. Kenneth Seidelmann, U.S. Naval Observatory, Washington D.C. University Science Books Mill Valley, CA 94941 1992 Library of Congress Catalog Number: 91-65331 ISBN 0-935702-68-7
"We also stand at a confusing crossroads for astronomy. In just the last few years the International Astronomical Union has introduced subtle changes in the reference frame used for the coordinates of celestial objects, both within and far beyond our solar system. So sweeping are these revisions that a highly respected work for professional astronomers, the EXPLANATORY SUPPLEMENT TO THE ASTRONOMICAL EPHEMERIS, published in 1961, is now seriously out of date. [The EXPLANATORY SUPPLEMENT TO THE ASTRONOMICAL ALMANAC, published in 1992 replaces this older work.] While the technical journals have seen a flurry of scientific papers on these issues, [Meeus' book] is the first to offer succinct and practical methods for coping with the changeover. It will be many years before astronomical data bases and catalogs are fully converted to the new system, and anyone who needs a detailed understanding of what's going on will appreciate this book's many comments about the FK4 and FK5 reference frames, 'equinox error,' and the distinction between 'J' and 'B' when placed before an epoch like 2000.0.
"Scarcely any formula is presented without a fully worked numerical example--so crucial to the debugging process. the emphasis throughout is on testing, on the proper arrangement of formulae, and on not pushing them beyond the time span over which they are valid. Chapter 2 contains much wisdom of this sort, growing out of the author's long experience with various computers and their languages. He alerts us to other pitfalls throughout the text. Anyone who tries to chart the path of a comet, for instance, soon encounters Kepler's equation. It has so vexed astronomers over the years that literally hundreds of solutions have been proposed; the striking graphs in Chapter 29 give a good idea why.
"We now live in a thrilling time for practitioners of the number-crunching art. The four-function pocket calculators that were so costly 20 years ago are now incorporated as a gimmick on certain wristwatches. The memory capacity of the 1K RAM board in the pioneering MITS Altair microcomputer is exceeded 500-fold by a single chip in some of today's laptop and notebook computers. Who knows what other marvels lie just ahead? By presenting these astronomical algorithms in standard mathematical notation, rather than in the form of program listings, the author has made them accessible to users of a wide variety of machines and computer languages--including those not yet invented".
The primary purpose of this 760 page (completely revised and rewritten to conform to the FK5 reference frame in current use) EXPLANATORY SUPPLEMENT TO THE ASTRONOMICAL ALMANAC is to provide users of THE ASTRONOMICAL ALMANAC with more complete explanations of the significance, sources, methods of computation, and use of the data given in the almanac than can be included annually in the almanac itself. The secondary purpose is to provide complementary information that doesn't change annually, such as conceptual explanations, lists of constants and other data, bibliographic references, and historical information relating to the almanac.
Many users of the almanac are not the professional astronomers for whom it is primarily designed, and so this supplement contains some explanatory material at an elementary level; it is not, however, intended for use as a basic textbook on spherical and dynamical astronomy. In some respects it does supplement such textbooks since it is concerned with new concepts or new techniques.
This supplement differs in many respects from its predecessor, the EXPLANATORY SUPPLEMENT TO THE ASTRONOMICAL EPHEMERIS AND THE AMERICAN EPHEMERIS AND NAUTICAL ALMANAC. Vector and matrix notation have been introduced and more diagrams have been provided. Simple conversion tables and tables of quantities that can be calculated directly from simple formulas have been omitted. Detailed step-by-step examples have been omitted, and approximation methods have not been given. Most of the text is new but historical material has been carried over for the convenience of those who do not have ready access to the previous supplement.
There is a tremendous amount of information and rigor in the EXPLANATORY SUPPLEMENT. The following chapters (and some sub-chapters) give a little insight into the content.
1. Introduction to Positional Astronomy
2. Time 3. Celestial Reference Systems
4. Terrestrial Coordinates and the Rotation of the Earth
The task of establishing or defining the terrestrial
coordinates of a point is inextricably linked to establishing
the rotation of the earth over time. The definition of any
terrestrial reference coordinate system is given by
establishing a celestial reference coordinate system and a
suitable transformation between them. This chapter includes
grid systems such as Longitude and Latitude, Universal
Transverse Mercator (UTM), Universal Polar Stereographic
(UPS), and so on, Geodetic Datums, and the Global Positioning
System (GPS). 5. Orbital Ephemerides of the Sun, Moon, and Planets
6. Orbital Ephemerides and Rings of Satellites 7. Physical Ephemerides of the Sun, Moon, Planets, and Satellites
8. Eclipses of the Sun and Moon9. Astronomical Phenomena 9.1 General Aspects of the Night Sky 9.2 Configurations of The Sun, Moon, and Planets 9.3 Risings, Settings, and Twilight 9.4 Occultations 9.5 Pole-Star Tables 9.6 References 10. Stars and Stellar Systems
11. Computational Techniques
11.1 Introduction to Computing Techniques
11.2 Interpolation and subtabulation
11.3 Plane and Spherical Trigonometry
11.4 Matrix and Vector Techniques
11.41 Rotation of Axis Using Matrices
11.42 Spherical Coordinates Using Vectors
11.43 Spherical Coordinate Transformations
11.5 Numerical Calculus
11.6 Statistics
11.7 References
12. Calendars
This section includes: Introduction, The Gregorian, Hebrew,
Islamic, Indian, and Chinese Calendars as well as Julian
Day Numbers and Julian Date, The Julian Calendar, Calendar
Conversion Algorithms and References.13. Historical Information 14. Related Publications 15. Reference Data
Glossary
Index
The last chapter, Reference Data, contains pages of Fundamental Constants, Time and Standard Epochs, constants relating to the Sun, Earth, and Moon, Geodetic Reference Systems, Planets: Mean Elements, Planets: Rotational Data, Planets: Physical and Photometric Data, Satellites: Orbital Data, Satellites: Physical and Photometric Data, Planetary Rings and on and on.
-Sam Wormley
http://www.edu-observatory.org/eo/algorithms.html
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