Janus is proud to announce publication of The Astrolabe.

The Astrolabe book cover

The astrolabe was the most popular and useful astronomical instrument from its introduction in the ancient world through the Renaissance. No device has ever matched the astrolabe's intuitive presentation of the sky and value for solving astronomical problems without calculation. An astrolabe is as an astronomical computer, an observation instrument, a star finder, a handy reference of celestial positions and a tool for astronomy education. Its rich history flows from Greek Antiquity through the Islamic world and into Medieval and Renaissance Europe.

The Astrolabe (Soft cover, 438 pp.) is the most complete astrolabe treatise available. It includes the description, history, use, theory and design of all types of astrolabes and several related devices, updated to modern methods and terminology. Application of computers to astrolabe design and practical advice on making an inexpensive working astrolabe are included.

The Astrolabe is an invaluable reference for anyone with an interest in the history of science and astronomy, the use and history of scientific instruments and, of course, astrolabes. It is an introduction to pre-telescopic instruments for the novice, a reference for teachers and professionals, a guide for designing reproductions and a source for researchers.

The Astrolabe is not a book about specific instruments. It covers the principles and design details of each instrument type. A few pictures of old instruments are included, but only to show how the principles are applied. There are many sources of pictures of historical instruments in books and on the web.

See below for ordering information.


The intent of The Astrolabe is to be clear, accurate and complete. Each topic is introduced in very basic terms and expanded with technical details as needed for more sophisticated subjects and applications. A summary of the latest historical research for each instrument and type of instrument is included.

Quadrans NovusAstrolabes are visual instruments and are best learned with a visual reference. There are more than 250 figures showing the details of each instrument and scale discussed.

The material on applications of computers to astrolabe design is unique. Most of the figures are computer produced and serve as examples of modern astrolabe design.

Also included are figures of the astrolabe components that can be copied and made into a working instrument.

If you like, you can download a PDF of a sample chapter. This chapter covers Gunter's Quadrant and illustrates the level of the overall content, the topics covered and the type of figures included. Keep in mind that the material in this chapter uses terms and ideas covered earlier in the book. Juergen Giesen used this sample chapter to create a unique interactive Gunter's Quadrant at http://www.GeoAstro.de/gunter/.


What is unique about The Astrolabe?

  1. It is the only astrolabe treatise to cover the design of all types of astrolabes completely.
  2. It contains the first complete discussion of astrolabe related quadrants in modern terms.
  3. It is the first publication that covers the differences between European and Islamic astrolabes in detail.
  4. It is the only book that describes how to make astrolabes for southern latitudes.
  5. It is the first publication to discuss the application of computers to astrolabe design and making a reproduction.
  6. It is the first astrolabe treatise to include both analytic and graphical methods for designing astrolabe related instruments and the only source having derivations of the layout equations.

What background is needed to understand The Astrolabe?

The astrolabe is an astronomical instrument, so a basic understanding of astronomy terms, such as declination, is helpful but not strictly required as the needed definitions are included. The mathematics of astrolabes is covered at the level of high school trigonometry, with a little basic analytic geometry (such as the equation of a circle). The math is included because it is needed to design an astrolabe. The math can be skipped if you don't want to make an instrument and returned to when needed. The computer related material ranges from very basic to some rather sophisticated programming examples. This material is intended to be useful to anyone who wants to design an astrolabe on a computer. Just ignore it if you don't.

Who are the intended readers?

Based on my experience with The Personal Astrolabe, most readers will be ordinary educated people with an interest in astronomy and its history who have become interested in non-telescopic instruments, such as sundials. I cannot describe a "typical" user of The Personal Astrolabe. Some have technical backgrounds. Many don't. As one might suspect, it is popular with amateur astronomers, medieval recreationists, planetariums and astronomy students. Many sailors have an interest in celestial navigation, which draws them to the old instruments. It seems to be particularly popular with physicians and many users have sailing and/or amateur radio as hobbies. My best guess is that such people just like gadgets, and few gadgets are more engrossing than astrolabes.

Another audience is teachers, particularly those who teach science, medieval history, basic astronomy and the history of science and need reference material in their personal libraries. Clearly, students of the history of astronomy should be familiar with the contents. I assume most scholars are familiar with much of the material, but they may find The Astrolabe to be a useful reference.

Comments from reviewers

Dr. Bruce Stephenson, Curator, Webster Institute for the History of Astronomy, Adler Planetarium & Astronomy Museum

Jim Morrison's wonderful book explains everything that can be said about the astrolabe and related instruments, including all the details of their construction and use. It is animated throughout by a cheerful faith that this preeminent tool of astronomers past can still play a role in 21st-century scientific education and practical life. If you have ever wondered "how an astrolabe works" (at any level of detail), this is the book that will tell you.

Dr. François Charette, historian of Islamic science and author of Mathematical instrumentation in fourteenth-century Egypt and Syria (Brill: 2007).

In The Astrolabe, Jim Morrison treats the noblest instrument of ancient and medieval astronomy with an enthusiasm and respect that is on a par with that of the great medieval scholars who wrote exhaustive treatises on its construction and use. There is no comparable book in the English language. It will be of interest to enthusiast laypersons, but I am also certain students and historians of pre- and early-modern astronomy will enjoy it as well.

John Lamprey - author of Hartmann's Practika (2002), and co-author of Stoeffler's Elucidatio (2007).

The Astrolabe by Jim Morrison promises to be THE STANDARD on the subject for years to come. Jim has been a reliable resource for me for many years in my studies and work in the field of astrolabes. Anyone that wants to look into all of the nooks and crannies of this fascinating subject will have to have his book.

Malcolm Barnfield. Sundial Maker, Johannesburg, South Africa

The Astrolabe is an exhaustive examination of the astrolabe, quadrants and other stereographic instruments, covering their history, theory, construction (including the mathematics), practice and usage. Following its precise instruction, I have successfully constructed a universal astrolabe and a double sundial. Projects I had never attempted before and I gained valuable trigonometric knowledge and understanding in the process.

I thoroughly recommend it to the novice and expert enthusiast alike.

Dr. Edward S. Popko, Woodstock, NY

The astrolabe is one of the most significant scientific instruments of all times. What other instrument has been in continuous use for nearly 2000 years? It solved the critical problems of its day and continues to be admired for its ingenuity and usefulness.

The Astrolabe focuses on the instrument itself. Morrison retraces the astrolabe's evolution over the ages and shows how their designs changed and their inscriptions evolved to serve its users. He even hints at its astrological uses where one's fate might rest with the rising or setting of a lucky star.

Morrison fast forwards the astrolabe to modern times. He shows how, with dedication, you can make your own surprisingly accurate and beautiful astrolabe. Everything is included: modern star positions, formulas for making graphics and examples of recently crafted instruments.

Anyone interested in the history of science or fields like astronomy, navigation or surveying will be astonished at the variety, beauty and utility of the astrolabe.

Morrison's book is beautifully illustrated, and supported by a series of useful and instructive appendices.

Col. Keith E. Brandt, M.D., ASAF Flight Surgeon at NASA's Johnson Space Flight Center.

I have read the majority of the books on western astrolabes and there is more packed into this volume than I've seen in a whole shelf-full of all the other astrolabe books. I don't just want to know about the historical instrument, I want one that I can use in the medieval way, but with accurate results. The Astrolabe is a treasure trove for making historically accurate instruments with full modern functionality. Not only astrolabes, but a whole host of other instruments I've never seen mentioned.

Ordering The Astrolabe

The Astrolabe is available on Amazon.com or directly from the publisher. If Amazon is out of stock or you would like a signed copy at a slightly reduced price, send a note to Janus at janus.astrolabe@verizon.net to make arrangements.

Contact the publisher, Janus at janus.astrolabe@verizon.net, for information on discounts

A hard cover edition published by Classical Science Press is now available. See http://www.classicalsciencepress.com/index.html for information and pricing. This edition will not be available on Amazon.

A few small details have been identified and fixed since the initial printing. Errata pages are available. Just send me the printing date of your copy, which is on the copyright page in small print toward the bottom of the page, and I would be happy to send any applicable corrections as a small PDF.

Very few books were produced in the first printing in order to provide a basis for any needed refinements.  The initial printing used a "perfect" binding which proved to be awkward and all copies printed since have a "lay flat" binding, which works much better for such a thick book. We have six copies left from the first printing that we are making aviailable to students and teachers in the US for the cost of postage - $8 US ( $9 US if payment is through PayPal). This offering does not apply to non-US readers because international postage for such a big book is quite expensive. The content of the book has not changed much but a few errors and some formating issues have been resolved.   The books will be shipped "as is" but including all errata.  All you have to do to get a copy is assure me that you are either a student or a teacher and figure out how to get your mailing address and the postage cost to me.

Here is the Table of Contents with a few of the figures from the book:


Astrolabe front Chapter 1 - The Astrolabe

What is an Astrolabe?

An Instrument with a Past and a Future

The Principle of the Astrolabe

The Parts of the Astrolabe


The Front of the Astrolabe

The Rete and Rule

The Back of the Astrolabe


An Illustrated Example

Types of Astrolabes


The Spherical Astrolabe

The Planispheric Astrolabe

Universal Astrolabes

Astrolabe Quadrants

Horizontal Instruments


Astrolabe Clocks

Computer Astrolabes

Chapter 2 - A Concise History of the Astrolabe

Foundations of the Astrolabe

Development of the Astrolabe


Prayer Times



Refinement of the Astrolabe

Decline of Astrolabe Popularity

Chapter 3 - The Stereographic Projection

Why the Astrolabe Works

Principles of the Stereographic Projection

Application of the Stereographic Projection to the Planispheric Astrolabe

The Half Angle Theorem

Stereographic Projection Proofs

Chapter 4 -The Planispheric Astrolabe Front

The Mater and Throne

The Limb

The Plate


Plate Interior

Twilight Arcs

Unequal Hours

Other Hour Arcs

Houses of Heaven�


Some Special Plates


The Plate of Horizons

Plate for 0 and 90

Plate of Ecliptic Coordinates

Chapter 5 - Drawing the Astrolabe Plate

The Equator and Tropic of Cancer

Horizon and Almucantar Projection


Graphical Horizon Construction

Altitude Circle (almucantar)Pprojections

Almucantar Center Projection

Graphical Altitude Circle (almucantar)Pprojections

Almucantar Alignment with Meridian

Almucantar Separation


Azimuth Arc Projections


Graphical Azimuth Arc Construction


Unequal Hour Arcs

Islamic Prayer Times

Equal Hour Arcs

Houses of Heaven

Other Graphical Layout Methods


The Dastur

Hartmann's Method

Chapter 6 - The Rete

The Ecliptic

Dividing the Ecliptic

Star Positions




A Modern Rete

A Celestial Navigator's Rete

Chapter 7 - The Rule

Making the Rule

Astrolabe back

Chapter 8 - The Astrolabe Back

The Back of European Astrolabes


The Altitude Scale

The Solar Longitude Scale

The Calendar

Eccentric Calendar

Drawing the Eccentric Calendar

Concentric Calendar

Making a Concentric Calendar

The Shadow Square

Drawing the Shadow Square

The Diagram of Unequal Hours

Using the Unequal Hours Diagram

Equal Hour Scale

Equal / Unequal Hour Conversion Scale

Using the Equal / Unequal Hour Scale

Drawing the Equal / Unequal Hour Scale


Islamic astrolabe back

The Back of Islamic Astrolabes


Shadow Scales

The Sine/Cosine Scale

Using the Sine/Cosine Scale

Making the Sine/Cosine Scale

The Cotangent Scale

Using the Cotangent Scale

Drawing the Cotangent Scale

The Arcs of the Signs

Drawing the Arcs of the Signs

Drawing the Sun's Noon Altitude Curves

The Graph of the Azimuth of the qibla

Drawing the Graph of the qibla

Other Scales on the Backs of Islamic Astrolabes

Lunar Mansions


Astrological Scales


A Modern Astrolabe Back


Using the Modern Astrolabe Back

Making the Modern Astrolabe Back

Chapter 9 - Sample Problems

Chapter 10 - The Astrolabe for Southern Latitudes

The Plate

The Rete

The Rule

Chapter 11 - Calculation Summary






How Accurate is an Astrolabe?

Chapter 12 - Universal Astrolabes

Saphea Universal Astrolabe

Chapter 13 - The Saphea Arzachelis

The Saphea Universal Astrolabe


Saphea Scales


Polar Arcs

The Regula and Brachiolus

Uses of the saphea

The Planispheric Astrolabe


Making the Saphea

The Lamina Universal and the "Mathematical Jewell"

Peter Apian's "Meteoroscope"

The Quadratum Nauticum

Chapter 14 - Orthographic Astrolabes

Rojas Astrolabe

The Orthographic Projection

The Organum Ptolemei

The Orthographic Astrolabe


The Origins of the Rojas Astrolabe


The Rojas Astrolabe


Using the Rojas Astrolabe

Making the Rojas Astrolabe


The Regula and Cursor

Chapter 15 - De la Hire's Astrolabe

Using the de la Hire Astrolabe

Making the de la Hire Astrolabe

Calculation Example

Chapter 16 - Quadrants


The Horary Quadrant (quadrans vetus)


History of the Horary Quadrant

Making a Horary Quadrant

Accuracy of the Horary Quadrant

Astrolabe Quadrand

Chapter 17 - The Astrolabe Quadrant


Introduction to the Astrolabe Quadrant

The quadrans novus

The quadrans novus arcs and scales


The quadrans novus Interior



Right Ascension


Using the quadrans novus

Position-Related Problems

Time-Related Problems

Making the quadrans novus

Gunter's Quadrant

Chapter 18 - The Prophatius Quadrant

Using the Prophatius Quadrant

Making the Prophatius Quadrant

Chapter 19 - Gunter's Quadrant



Using Gunter's Quadrant

Making Gunter's Quadrant

Sutton's Quadrant

Chapter 20 - Sutton's Quadrant



Using Sutton's Quadrant

Using Sutton's Quadrant

Making Sutton's Quadrant

Sutton's "Small Quadrant"

Chapter 21 - Horizontal Instruments



Hartmann's "Compast"

Time Measurement with the Horizontal Instrument

Oughtred's Double Dial

Using the Horizontal Instrument

Using the Double Dial

Making the Horizontal Instrument

The Horizontal Projection Quadrant


Chapter 22 - Astrolabe Variations

van Maelcote's Astrolabe

Using van Maelcote's astrolabe

Making van Maelcote's Astrolabe

The Linear Astrolabe of al-Tūsī

Islamic Astrolabe Variations


Making a Planisphere

Other Astrolabe Related Devices

Chapter 23 - Astrolabe Clocks

Monumental Astrolabe Clocks

Personal Clocks with Astrolabe Dials

The Ulysse-Nardin "Astrolabium Galileo Galilei"

Chapter 24 - Astronomical Background

The Celestial Sphere


Equatorial Coordinates

Ecliptic Coordinates



The Sun's Position


Telling time

Sidereal Time

Chapter 25 - Astronomical Calculations

Tranformation of Coordinates

Time in Astronomical Calculations

The Sun's Position

Stellar Precession

The Equation of Time

Calculating Time

Chapter 26 - Computers and Astrolabes


Simple Astrolabe Programs

Some useful routines


Chapter 27 - Design, Layout and Fabrication


The Back

Fabrication Alternatives

Appendix - Star Positions

Appendix - Solar Data






There was almost nothing available about astrolabes when I first became interested in them more than 30 years ago. At first, all I wanted was a reference that explained how and why astrolabes work and a guide to understanding the scales on old instruments. I quickly moved on to wanting to understand how to draw the astrolabe scales, but there was nothing available. I went so far as to translate Henri Michel's Traité de l'Astrolabe into English in an attempt to get what I needed. It was an interesting and rewarding challenge, especially since my French is not all that good, but the result was still short of what I felt I needed, particularly in the analytic design details, so I had to do it myself. It was frustrating but fun to work out the math to design an astrolabe and to write programs that would draw a working instrument. I was fortunate that my work required frequent trips to Europe and I was able to establish relationships with some of the scholars who have studied the evolution and history of pre-telescopic instruments and, through them, began to tap into to the historical literature.

Then, as they say, one thing led to another, and I devoted myself to learning all I could about all types of astrolabes and their history. The lack of readily available information about astrolabes led to starting this web site and offering The Personal Astrolabe and The Electric Astrolabe in an ongoing attempt to make astrolabe information more accessible.

I wanted to produce the book that I wished had been available when I was getting starting and would be interesting and useful to any educated person with an interest in astrolabes, regardless of background.

The Astrolabe is the culmination of that effort.