The Electric Astrolabe

The Electric Astrolabe is a fully animated planetarium program in the form of a planispheric astrolabe. The singular advantage of the astrolabe display is that it shows most of the sky, both visible and invisible, on a single screen. Unlike a static instrument, The Electric Astrolabe can be set for any location, date and time and includes accurate positions of the Sun, Moon, and planets. In addition, The Electric Astrolabe includes over 150 stars which can be displayed as constellation asterisms and all of the Messier objects. Either a north or south projection can be shown. You can also display the phase of the moon, Jupiter's moons, Saturn's rings, lunar eclipses and the phases of the planets at any time. The color of the sky above the horizon changes from blue, through twilight gray to black depending on the position of the Sun. The picture below is a screen saved from The Electric Astrolabe set for the instant Neil Armstrong first set foot on the moon as seen from the Manned Spaceflight Center in Houston.

Also included are an animated orrery showing the planetary orbits and several text screens giving accurate solar, lunar and planetary positions, a help screen and several screens for customizing the program to your location and choice of colors and making it easy to use. Text entry screens are implemented as a sort of astronomical spreadsheet. That is, changes to a value cause all related values to be updated automatically.

[Electric Astrolabe Screen]

For beginners, The Electric Astrolabe can be used as an educational tool to learn about astronomical measurements and the astrolabe display provides a very effective way to understand basic astronomy principles. The animation ability of The Electric Astrolabe provides vivid demonstrations of the motion of the Sun, retrograde motion of the planets, stellar precession and the astronomical reasons for the changing seasons. For advanced users, The Electric Astrolabe can calculate planetary and lunar positions with an accuracy close to The Astronomical Almanac including provision for dynamical time. The Electric Astrolabe can be used to plan astronomical observations, determine the exact time of astronomical events for any date and location, plan events to coincide with the phases of the moon or simply stay in touch with what is happening in the sky. The Electric Astrolabe also makes an extremely elegant astronomical clock.

The Electric Astrolabe has been described in "The Electronic Astrolabe", Interdisciplinary Science Reviews 19.1, (March, 1994) and "Updating the Astrolabe", Festschrift for the 50th anniversary of the Institute for the History of Science, Johann Wolfgang Goethe University, Franz Steiner Verlag, Stuttgart (1994). It is on public display in the astrolabe collection at the Frankfurt, Germany City Museum.

It is a DOS program, but has been tested and runs very nicely under all versions of Windows (but see below for Vista and 7). It has been reported that The Electric Astrolabe can be run under Mac OSX using DOSBox (see below). An Intel 386 or later processor with a math coprocessor is required. VGA and SVGA graphics are supported using either direct hardware control or VESA. It is written entirely in assembler language (about 30,000 lines of code). This program was written a long time ago and some of the astronomical references may seem a bit dated. A few of the hundreds of new users have reported some details that needed attention. I am fixing them as they are reported. Please let me know if you have any problems with either the program or the documentation and I will try to make needed modifications.

The Electric Astrolabe has been used by thousands of individuals and schools around the world and, as far as I know, has never caused a computer related problem. It is very easy to install and use, but it does incorporate some rather sophisticated facilities related to time and planetary positions. It has been proven to be a very effective learning tool for astrolabes, positional astronomy and the principles of timekeeping, but experience has shown that it actually helps to read the user's guide. I would appreciate a note if you use The Electric Astrolabe in a public display, school or mention it in a newsletter or other publication. There is no charge for any use, but I like to keep track of where and how it is used.

You can download The Electric Astrolabe and documentation if you want to try it out (last updated July 24, 2013). You can also download just the executable file ( to get the latest version if you already have the user's guide. The latest updates include higher precision display of Delta-T and a change to make manual mode date and time display better under DOSBox. The program is very stable and will no longer be updated.

No support assistance is available (please see the note on the home page). If you need help, you might try an Internet search. We honestly don't know what you'll find.

The Electric Astrolabe is completely free, not shareware, and is distributed as a courtesy with no warranty of any kind. The download file ( is a .zip file of about 920 Kb. is about 72Kb. Installation is trivial. Simply copy the downloaded file to a new folder and unzip the file. will expand into the executable program (astro.exe), the user's guide (using.pdf) and several other files that are described in the installation instructions (eainstall.doc). The user's guide is 115 pages. Unzipping will result in the executable program (astro.exe). You can run the program from this file, but you will find it to be a bit difficult to use without the user's guide.


DOSBox is a free DOS emulator that allows you to run DOS programs under Windows, Linux, Mac OSX, Windows Vista, Windows 7 and possibly other platforms.

You cannot run The Electric Astrolabe natively under Windows Vista or 7, which probably makes sense to Microsoft but not to me. It seems to work fine with DOSBox under Vista and 7. You can download DOSBox from

It is very easy to use. Instructions for setting up The Electric Astrolabe with DOSBox are in the User's Guide.  Be sure you have the latest DOSBox version (0.74 at this writing) and refer to the dosbox.cnfg file in the Electric Astrolabe distribution file ( for installation options.  The Electric Astrolabe User's Guide has the details.

Following are some hints to make it easier to operate The Electric Astrolabe to its full potential under DOSBox.

# Lines in this section will be run at startup.
mount c c:\astrot (Use the path of your folder with EA)



The "cycles" entry tells DOSBox how much is executed in each cycle.  I found 20000 works fine on my 2.5 GHz laptop and 16000 is better on my bigger and faster system.  You will have to experiment to see what works for your computer.  cycleup and cycledown are the increments to use with Ctl+ F11 and F12.

The name "The Electric Astrolabe" is derived from the Tom Swift stories that were popular in America around the turn of the 20th century. Tom Swift was a creative boy who used the latest technology (for the time) to solve crimes. Many of the stories had titles such as, Tom Swift and his Electric Locomotive or Tom Swift and his Electric Compass. I'm sure that Tom Swift would have had an electric astrolabe if he had thought about it.