Zodiacal constellation boundaries

The heliocentric ecliptic coordinate system of the Human Orrery provides an introduction to astronomical frames of reference. When we designed the exhibit, we wanted the zodiacal constellations to be indicated. However, whereas the Orrery is laid out in the ecliptic plane, constellations are defined in B1875 equatorial coordinates. Therefore for each adjacent pair of zodiacal constellations, we calculated the point at which the J2000 ecliptic intersects the boundary between the two constellations. This point is given in the table, in both B1875 equatorial and J2000 ecliptic coordinates (ecliptic longitude only, since the latitude is zero). All values are in decimal degrees. We see that the largest (in this sense) zodiacal constellation is Virgo, at 44 degrees (its boundary with Leo being at 173.851 and with Libra at 217.810).

Calculations by David Asher with a program that made use of SLALIB subroutine libraries.

B1875 J2000
RA dec Longitude
Pisces numbers plot image 
  25.0   
  10.381 
    28.687

Aries numbers plot image 
  49.25  
  18.181 
    53.417

Taurus numbers plot image 
  88.25  
  23.430 
    90.140

Gemini numbers plot image 
 118.25  
  20.903 
   117.988

Cancer numbers plot image 
 138.75  
  15.955 
   138.038

Leo numbers plot image 
 172.75  
   3.134 
   173.851

Virgo numbers plot image 
 213.75  
 -13.541 
   217.810

Libra numbers plot image 
 237.092 
 -20.0   
   241.047

Scorpius numbers plot image 
 244.0   
 -21.289 
   247.638

Ophiuchus numbers plot image 
 264.0   
 -23.324 
   266.238

Sagittarius numbers plot image 
 300.0   
 -20.580 
   299.656

Capricornus numbers plot image 
 328.0   
 -12.941 
   327.488

Aquarius numbers plot image 
 350.723 
  -4.0   
   351.650

Pisces numbers plot image

Strasbourg: constellation boundaries
Jim Kaler: constellations

Last Revised: 2020 August 1st