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: 2015 February 27th