A Precise and Customizable Planisphere

This project generates a precise, customizable planisphere as two PDF files (a star chart and a transparency). The two files are then printed on a high-resolution printer, and the results are attached together in the center with a rivet. One file is meant for printing on card stock, and the other as a transparency. The transparency rotates around a central rivet or pin.

The source code is here.

The planisphere uses the stereographic projection, which is appropriate only for latitudes outside the tropics. (That is the main defect of this projection.)

The output is configured using a config.ini text file. A number of minor settings, which most people would not want to change, are hard-coded.

How To Make The Planisphere

Generate the PDF files using a form on the web (which uses this project's code): Or, if you download this project's source code, you can generate the PDF files using a stand-alone program, from the command line:


Cut, puncture, and attach:

Verify the centering. Examine the intersection of the celestial equator with the horizon. As you rotate the transparency 360 degrees, the intersection point of the celestial equator with the horizon should always coincide with the east-west point.

Design Goals

The main design goals of this planisphere are:

For years other than that for which the planisphere was generated, the precision will of course be significantly reduced.

Planispheres are seldom expected to be precise. Nevertheless, it's always interesting to push an instrument to its limits, to see how far you can go. That said, many people will be perfectly content with planispheres having significantly lower precision.

What's Included

The planisphere's star chart includes (example PDF, with the star chart on page 2):

The tables for the Moon and bright planets are used to get approximate positions for those objects over the course of the configured year.

The planisphere's transparency goes on top of the star chart. The transparency includes (example PDF):

Higher Precision

An effort has been made to make the planisphere as precise as possible:


There are two small discontinuities in the planisphere (by design), which bear witness to the astronomical reality:


Notes about the implementation:

Tools Used

Items used in building this tool:

What I Learned

Things I learned while building this tool:

Things I'd like to have:

Explorations Over Long Time-Scales

Movement of the Poles

The motion of the poles of both the equator and the ecliptic can be robustly demonstrated with this code, since it uses a robust algorithm for long-term precession, published in 2011. (See the BuildPolePrecession class.)

Here are examples of the motion of the poles going back into the past 38,000 years, in steps of 200 years at a time. Note how both poles move. The ecliptic pole is the smaller, darker arc near the center.

(Note that the above charts don't include proper motion of the stars. See below for charts that include proper motion.)

Most images meant to demonstrate long-term precession are mediocre for two reasons: they show a closed loop, and they neglect altogether the motion of the ecliptic pole.

Year of Closest Approach to the Equatorial Pole

These are the raw results rounded to the nearest arcminute, using data from Hipparcos-2 astrometry, with full 3D kinematics for proper motion. The error bars in the underlying data are not used in these calculations.

See the underlying paper (Figure 11) for estimates of the accuracy of the precession algorithm over long time scales.

This data was generated using the ClosestApproachToPole class.

For the years -100,000..+100,000 in the northern sky:

 Star  Year   Separation
α Lyr +89851  0°18' Vega
α Cyg -40834  2°52' Deneb
α UMi -74968  0°00' Polaris 
β UMi -27240  2°09' Kochab
α Cep +58105  0°05' Alderamin
λ Cep -44141  0°15' 
α Dra - 2796  0°06' Thuban
τ Her - 7607  0°32' 
On the time-scale of +/-100,000 years, the error of the precession algorithm is about 300 arcseconds (5 arcminutes).

For the years -100,000..+100,000 in the southern sky:

  Star  Year   Separation
α  Dor -32064  4°05' 
γ  Dor -31862  0°40' 
α  Eri +73449  3°50' Achernar
γ  Cha -22453  0°12' 
α  Car +91325  5°25' Canopus
ω  Car -71400  0°06' 
δ  Vel + 9245  0°10' Alsephina
γ2 Vel +36629  0°08' Regor
σ  Pup -14093  0°23' 

For the years -15,000..+15,000 in the northern sky:

 Star  Year   Separation
α Lyr -12049  3°26' Vega      chart
α Cyg +10202  7°27' Deneb     chart
α UMi + 2102  0°28' Polaris
β UMi - 1059  6°32' Kochab    chart
α Cep + 7539  1°55' Alderamin chart
λ Cep + 7319  4°55' 
α Dra - 2796  0°06' Thuban    chart
τ Her - 7607  0°32'           chart
On the time-scale of +/-15,000 years, the error of the precession algorithm is about 50 arcseconds.

For the years -15,000..+15,000 in the southern sky:

 Star  Year    Separation
α Dor  - 6963  9°08' 
γ Dor  - 6869  4°58' 
α Eri  - 3360  6°59' Achernar
γ Cha  + 4125  1°32'           chart  
α Car  +13844  7°27' Canopus   chart  
ω Car  + 5788  0°46'           chart
δ Vel  + 9245  0°10' Alsephina chart
γ2 Vel -15000  2°33' Regor
σ Pup  -14093  0°23'           chart

Times in History

 Year   Description                Chart
+ 150   Ptolemy of Alexandria     chart
-2796   Egypt (Thuban at pole)    chart
- 590   Thales of Miletus         chart
-8000   Neolithic revolution      north, south  
Interesting: Orion isn't visible in mid-northern latitudes, in the year -8000.