Return to Select a Calculation |
|
Return to Tutorials |
|
Return to Home |
|
Maintained by Ray Shapp Page last updated 06/23/2001 |
Path: news.compuserve.com!news-
Newsgroups: sci.astro.amateur
Subject: (FAQ) Astronomical Calculations for the Amateur
Date: Wed, 01 Dec 1999 14:36:43 GMT
Organization: Posted via Supernews, http://www.supernews.com
(FAQ) Astronomical Calculations for the Amateur
ASTRONOMICAL SOURCES
|
This FAQ is limited to questions about calculating planetary positions and related problems of spherical astronomy. Other areas of interest, such as calculations of telescope optics, are beyond the bounds of this document. Calculation of astronomical events is a vast field with literature stretching back centuries, even to ancient times. This "frequently asked questions" list is directed toward the amateur astronomer who is looking for starting points. If you become familiar with the first two books recommended below, you will be well on your way. You will, in fact, have surpassed the author of the FAQ! The author of these FAQs is unknown. Additional info is available on the Tutorials section of this website as well as in the Other Links section. (RAS) ---------------------------------------------
1. What is a good source of books and software? ------------------------------------------------------------------------ 1. What is a good source of books and software? The Willmann-Bell (http://www.willbell.com/) printed catalog has a large section on "Computational "Astronomy", as well as many other astronomy books, atlases and telescope-making supplies: Willmann-Bell Inc Monday-Friday, 9AM-5PM Eastern time If you have access to a good library, books under the subject headings "Spherical Astronomy" and "Celestial Mechanics" would be the places to start. 2. What is the best beginner's book? Astronomical Algorithms by Jean Meeus, Willmann-Bell, Second Edition 1998, $24.95. Although it requires some study, this is the closest thing to a "cookbook" approach I have seen. Better than that, it explains and makes comprehensible many difficult concepts, and has many worked examples and illustrations. It is not restricted to elementary problems, but treats many advanced topics. No calculus is required. Beginners face two obstacles before they can calculate anything useful: (1) they must learn to convert between civil and astronomical dates and times (a task made more difficult by the fact that the Earth's rate of rotation is variable), and (2) they must learn a number of translations between coordinate systems (Sun-centered to Earth-centered to location-centered, as well as ecliptic to equatorial to horizon) and the application of corrections for precession and nutation and parallax. This is why questions such as "How do I predict the location of the moon?" do not have simple answers. You must know how to do (1) and (2) before you can start on the moon. The proper order of corrections and coordinate conversions had previously been very confusing for me, but Meeus gave me everything I needed to overcome these obstacles. He covers the basics of time and coordinate transformations, corrections for precession and nutation, and for the observer's true "topocentric" location as offset from the center of the Earth. For any given time, you can predict the positions of the Sun, Moon and planets and derive all the normal phenomena of the almanac. You can derive physical ephemerides (that is, the orientation of the objects as seen through a telescope) for the Sun, Moon, Jupiter, Mars and Saturn's rings. He provides both low-precision and high-precision techniques for charting Jupiter's four largest moons. The Keplerian techniques of dealing with the orbits of new bodies such as comets and asteroids are also given. A software supplement was available for the first edition, but this is no longer the case. 3. How much computer power does it take to perform these calculations? Modern personal computers, especially those with floating point hardware, are very capable machines. Calculating the position of all the planets several different ways, using Meeus' techniques, takes my 68040 a small fraction of a second. Performance on a PowerPC or Pentium would be stunning. 4. What is a more advanced reference work? Explanatory Supplement to the Astronomical Almanac, edited by P.K. Seidelmann, University Science Books 1992, 752 pages, $65 (available from Willmann-Bell). "Completely Revised and Rewritten", so make you sure you get the 1992 edition. This explains how the data in the annual "Astronomical Almanac" is produced. It is also a high-quality spherical astronomy text with many references to the current research literature. If you've read Meeus and want "more", this is the logical next step. Note that it contains very few worked examples and the math is much more advanced than in Meeus. Some of the chapters deal with issues of the professional astronomer that will not usually concern the amateur. Examples: plate tectonic motion can cause an observing site to shift its position several centimeters per year. Ocean tidal pressure on the continental shelves, and atmospheric pressure above the continents, can cause elevation to vary by similar amounts. Note also that they use a different method of calculating planetary positions than does Meeus. 5. Are there any relevant periodicals for amateurs? Sky & Telescope magazine has an astronomical computing column. Astronomy publishes programs from time to time. Willmann-Bell sells back issues of Celestial Computing, "A Journal for Personal Computers and Celestial Mechanics", dated from 1988 through 1992, edited by David Eagle. This is no longer published. The Computing Section of the Association of Lunar and
Planetary Observers (A.L.P.O.) has a Computing Section and an
electronic journal called The Digital Lens: 6. Where are online sources of algorithms? Sky & Telescope maintains an archive of program sources which
have appeared in the magazine: Unfortunately, these consist of uncommented BASIC listings.
Pseudo-code articles would be of greater use to those trying
to understand the calculations. Astronomy magazine provides a
small set of BASIC programs: Keith Burnett (keith@xylem.demon.co.uk) maintains an
"Approximate astronomical positions" web page containing
algorithms and many links: Paul Schlyter (pausch@saaf.se) has a "Calculating Planetary
Positions" web page at: Sites listed in the next topic also have software. 7. Where are online sources of data? There are astronomical amounts of data online. Try these web sites as starting points: o Astronomical Data Center home page 8. What commercial and shareware programs are available? o The freeware ephemeris program "ephem" for PC by Elwood
Charles Downey (and VGA `Watch' plots by J.D. McDonald)
is available at: (self extracting archive.) The same site carries many other ephemeris programs also for other platforms. (Nov 15 1997) There is a Web page for the Motif version
at: o (Dec 7 1995) Dave Lane, Nova Astronomics (dlane@ap.stmarys.ca) says I have recently completed a freeware program which might interest you. It's called the "Windows Ephemeris Tool" and it calculates tables of positions (and other data) for comets and asteroids. It's available at: o Willmann-Bell sells several software supplements which
have ephemeris capabilities. See their catalog ([1]
above) for details. |
|
Return to Select a Calculation |
|
Return to Tutorials |
|
Return to Home |
|
Maintained by Ray Shapp Page last updated 06/23/2001 |