Keith Powell's Astrolabe home page

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Please note that to see the Astrolabe you will need any version of Internet Explorer and Java up to version 8

If you can see this message you will not be able to run the Java Applets on this page

If you had a Java-enabled browser, you would see an image map allowing you to jump to pages having my applets. You can enable Java Applets for this website if you are using Internet Explorer 11 (or below) - you need to use the Java Console to set this site up on the 'Exception Site List' - instructions are here

Keith's Astrolabes

The java applet provided by this page displays modern versions of four types of medieval astrolabe. You can explore the many features of these on your computer where the menu and buttons allow you to select different features. You can also construct the astrolabes after printing out the components on paper and film.

The Java applet was originally written in 1999 to 2002, after which version v74 was displayed here. It was updated in February 2012 to correct errors concerning the planets, particularly the moon, when the version was adjusted to v74xx.

You need a Java-enabled browser to see Java applets. See top of page for instructions. If you had a java-enabled browser, you could see: my representations of four types of astrolabe.

Information files

If you want to read my astrolabe information files, start by looking at the: information file index.

The information files explain how to use the different astrolabes supported by this program, and provide information on various aspects of astrolabes. They also explain how to print and construct 'paper' versions.

About Keith's Astrolabes

In medieval times, astrolabes were used to measure the position of the Sun or a star and thence to find the time. They were also used to find precisely where the Sun and certain stars were located at any date and time throughout the year. However, a skilled operator could use an astrolabe to discover a great deal more.

My original purpose in writing the program which displays the java applet was to use it to explore the many facilities which medieval astrolabes provided. I hope you will now want to use itto do the same.

Before you start to experiment freely with the buttons, menu and keyboard keys, I recommend that you increase the size of the astrolabe window to make it as large as possible. Note that the 'Reset' button on the button panel allows you to reset all of the settings to their initial values.

The program shows freely adapted versions of four types of medieval astrolabe:

  • a conventional astrolabe
  • an equinoctial astrolabe
  • a spherical astrolabe
  • a universal astrolabe

Many of the features of these astrolabes can be varied. For instance, the conventional and equinoctial astrolabes can be set to suit almost any latitude in the Northern and Southern hemispheres.

As the centuries are changed by holding down the year +++ or --- buttons, you will see the stars precess, or the position of the offset calendar scale on the back of the astrolabe move as it is affected by the slow rotation of the earth's perigee. (Only the Gregorian calendar is currently supported.)

Another Astrolabe Web Site

In my opinion, the best site on the internet concerned with astrolabes is James E Morrison's web site at

As well as details of an astrolabe you can purchase and a PC DOS program you can download, you will find pages covering many aspects of astrolabes, including:

  • Collections,
  • History,
  • The Stereographic Projection,
  • The Parts of an Astrolabe,
  • Uses of the Astrolabe,
  • The Astrolabe Quadrant,
  • and the less common types of astrolabe.

Links and References are at

You can email me at (Sorry, you can't click on this.)