Details
Participants are invited to recreate the figures of the constellations adhering to (at a minimum) the descriptions and coordinates given in the critical editions of the Almagest. This means that the positions of the stars should be rendered accurately from the given coordinates and the figure drawn on top of/around it.
We encourage participants to engage in research beyond this starting point and incorporate elements from other period sources (provided they still adhere to Ptolemy’s descriptions for the positions of the stars within the figure) such as other period descriptions of the constellations, illuminations from astronomical/astrological manual, murals, mosaics, etc….
Entries may be done in any visual medium.
Timeline
To help establish structure for the project, we will be following the zodiac signs throughout the annual cycle, beginning with the vernal equinox on March 20, 2024. Participants will have one month to complete each constellation before the next one in the cycle begins.
The list of constellations and their date ranges is as follows:
Aries (March 20 – April 19)
Taurus (April 20 – May 20)
Gemini (May 21 – June 20)
Cancer (June 21 – July 22)
Leo (July 23 – August 22)
Virgo (August 23 – September 22)
Libra (September 23 – October 22)
Scorpio (October 23 – November 21)
Sagittarius (November 22 – December 21)
Capricorn (December 22 – January 19)
Aquarius (January 20 – February 18)
Pisces (February 19 – March 20)
Submissions are due by the last day of each zodialogical month. Later submissions will be accepted.
A drawing of the constellations depicted in a copy of the Almagest from 1532.
Necessary Information
The Short Version
The necessary descriptions of the stellar positions and coordinates can be found here. You will need to plot the star positions either using a computer or by hand. To do so, use the ecliptic longitude as your x-axis and the ecliptic latitude as your y-axis. More details on the variations of the different columns for longitude and latitude is below.
WARNING
Ecliptic longitude runs right-to-left instead of left-to-right (i.e., 0 should be on the right and the maximum of 360º should be on the left).
If you are starting by plotting the data in Excel, you can reverse the x-axis following the instructions here.
Begin with the stars laid out following these coordinates and use the descriptions of where each star is in the figure of the constellation to form your imagining of the constellation appropriately.
As you're working, take note of any stars that you feel are especially difficult to work into your drawing based on the description. The identity of some stars is uncertain (especially faint ones) and the star may have been misidentified (I've highlighted the instances in which authors disagree) and thus have the wrong coordinates (or I entered them incorrectly)! We will discuss these sorts of findings as the project progresses.
The More Detailed Version
The coordinates are given in ecliptic longitude and latitude. These work precisely the same way as latitude and longitude on the Earth with the exception that the fundamental dividing line between north and south is the sun’s annual path around the celestial sphere (the ecliptic) instead of the equator and we start on that line from the position of the sun on the vernal equinox instead of Greenwich.
The information here comes from a variety of sources. The translations of Ptolemy's descriptions come from Toomer's 2nd edition translation of the Almagest (1998). The coordinates are based on Gerd Grasshoff's History of Ptolemy's Star Catalogue (1990). However, these are not the coordinates from Ptolemy's star catalog (as those are known to have some significant errors even beyond the textual corruption). Rather, these are the calculated positions of the stars Grasshoff believes to be the ones to which Ptolemy was referring. These positions were calculated using modern astronomical theory and should give the best representation of what the sky actually looked like.
However, Grasshoff gave the coordinates for 128 BCE as the main topic of his book was investigating whether or not the data in Ptolemy's catalog was original or stolen from an earlier astronomer, Hipparchus, who lived in that time. Since these coordinates are not correct for Ptolemy's time, I have updated them accordingly for 137 CE, which is the year Ptolemy gives for his catalog.
Column Information
For the ecliptic longitude, I give the values in three different forms.
Sign & Sexagesimal Degrees
Ptolemy divided the ecliptic into 12 equal parts of 30º each - one for each sign. He would then list which sign the star was in and how far into that sign (a maximum of 30º at which point it would become 0º into the next sign). Thus, to know exactly where this is in the ecliptic, you'll need to know the order of the zodiac.
However, the portion of the value that is not a whole number is expressed in sixtieths (sexagesimal) instead of base-10 (decimal). These portions are denoted by the use of a semi-colon (;) to separate the whole number from the first division, known as the “minutes.” Unsurprisingly, this is the same way we measure time. Ex: 10;30º (10 degrees and 30 minutes) is the same thing as 10.5º. (ten and a half degrees).
Sexagesimal Degrees
For ease of use, I have added a column which removes the sign, instead giving the position as number of degrees out of the full 360º circle of the ecliptic but still in sexagesimal.
Decimal Degrees
To make the data easier to ingest with a computer (if you'd like to graph things out digitally to get started) I've also converted them to decimal, again in terms of the full 360º circle instead of each sign.
This value is given again in sexagesimal as well as decimal (see longitude section of explanation). The value can be either north of the ecliptic (which will be given a positive sign) or south (negative).
The magnitude is the brightness of the star. Here, 1 is the brightest and 7 is the faintest capable of being seen with the unaided eye. Ptolemy claims the catalog is a complete listing of all stars visible from Alexandria, Egypt where he worked, down to 6th magnitude, but this is not true as many are excluded.
WARNING
Some values have a > or < symbol. These are meant to indicate that the star is brighter than or less bright than the listed magnitude, but not as bright or faint as the next one. While I have adopted this formalism from the authors, I personally find it confusing as the symbols are applied to the magnitudes (which get larger as the stars get fainter) but are describing the brightness. Thus >4 would indicate a star brighter than 4th magnitude such as 3.7, opposite of what the symbol would seem to indicate.
HISTORY TIP
Modern star maps use different size dots to represent the brightness of stars with larger dots being brighter. Ptolemy instructs readers to do precisely this in his instructions for building a celestial globe, but it is not always done in all period drawings. Thus, if you are attempting to mimic a particular period depiction, you may wish to consider whether yours did or not!
For completeness, I have included the modern designations for each star based on the opinions of two different authors understanding of which they were intended to be. The first identification is by Grasshoff and is the one on which the calculated coordinates are based. For comparison, I also offer the identifications from Toomer to allow for easy identification of identifications which are highly uncertain in the event that things don't want to fit well.
HISTORY TIP
In modern astronomy, stars are often named using a catalog designation. Where possible I have given the identification of the stars using the Bayer designation. This system of identifying stars came from John Bayer's Uranometria which was published in 1603 and was based on data from Tycho Brahe, produced in period using pre-telescopic instruments! These designations always start with a Greek letter followed by an abbreviation for the constellation.
Sometimes, the star in question didn't have a Bayer designation in which case I try to use the Flamsteed designation. You can tell which ones these are because they start with a number followed by an abbreviation for the constellation.
Occasionally, you may also see a star designation beginning with BSC which indicates the designation is based on the Yale Bright Star Catalog.
Lastly, if an object stars with "M" followed by a number, this its designation in the Messier Catalog. This was a list of objects compiled in the 18th century by French astronomer Charles Messier who was hunting for comets. Because it's hard to distinguish between a fuzzy comet and other fuzzy things in the sky (like galaxies and nebulae) the way to tell the difference is to see if they move with respect to the background stars from night to night. If they do, it's a comet. Messier kept a list of things that weren't comets so he wouldn't get confused. Ironically, he became more famous for his "not-a-comet" list than he did for any comets he discovered because this list is full of fun deep sky objects easily accessible to beginners.
For those interested, a more complete version of the star catalog, comparing different historical manuscripts as well as modern critical editions can be found here (NOTE: The additional information found in this catalog will not be helpful for this project, but is provided for those interested in the history).