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computers in astronomy


Java Applets for Astronomy

A German schoolteacher writes astronomy programs for distribution over the Internet | By Adrian R. Ashford

   JAVA, SUN MICROSYSTEMS FLAGship programming language, has a favored status on the Internet because it is easy to learn, versatile, and "portable" _ that is, programs can run on various systems. With several computer hardware platforms and operating systems vying for market share, programmers wishing to write software that can be used by just about everyone have seen the obvious benefits of Java. These features have made it popular among those developing software for the World Wide Web.
  Most Web surfers will have encountered "applets" _ small Java-based routines embedded within Web pages _ often without realizing it (unless you notice when your Web browser pauses and the message "Starting Java" appears in a corner). These programs usually require no more than a recent browser to run. Applets bring interactivity to a Web page by combining text, graphics, animation, and sound, greatly enriching the online experience by overcoming the limited graphical capabilities of HTML. Users can access an applet with a wide variety of computer architectures and Internet browsers, assured of seeing information in essentially identical formats whether they're using Windows, MacOS, or Unix/Linux. 
   Java is relatively new and still evolving, so it lacks some features that are present in established languages such as C or Pascal. Its limited native support for complex arithmetic means many algorithms have to be written from the ground up for math-intensive functions. However, this hasn't stopped many people from generating Web-based software for scientific purposes. One of the most prolific writers of Java applets for astronomical use is Juergen Giesen, a 56-year old high-school teacher from Welver, Germany. His Web site (www.jgiesen.
de/GeoAstro/GeoAstro.htm) delivers


German high-school teacher Juergen Giesen (foreground) discusses the finer points of Java programming with his students. He is the author of an online astronomical Java applet collection. Courtesy Juergen Giesen.

a veritable cornucopia of original software of astronomical interest.
   Giesen's computing career dates back to 1965, when he programmed a Zuse Z23 in ALGOL. Subsequent work with FORTRAN on IBM and UNIVAC machines led to a thesis on the physics of metals in 1975. He started teaching highschool mathematics and physics two years later. An encounter with an Apple II in the late 1980s instilled a passion for later Macintosh personal computers that persists to this day; that, and a desire to program in Pascal.
   Realizing that the Macintosh platform and being a practitioner of Pascal placed him in a small but select group, Giesen started working with Java in a bid to extend the audience of his work. Now his prolific efforts in the field of Java applets have won him much more praise and recognition than from just his students.

 The wide-ranging appeal of his positional astronomical calculations concerning the Sun, Moon, and beyond have garnered attention from all over the world.
   A prerequisite for perusing this applet site is a Java-enabled browser such as Microsoft Internet Explorer 4, Netscape Navigator 4, iCab 2.4, or others. Even so, do ensure that Java is enabled in your software's preferences before visiting the site. The visitor can choose English or German versions of each page, which offer copious links to Giesen's other astronomical interests and those relating to physics.
   The complete set of applets may be previewed on the home page as GIF images showing typical output, or the applets themselves may be run online. Users can download a demo version of each applet or purchase a registered version for use offline. The complete GeoAstro Collection


58 June 2001 | Sky & Telescope

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