# 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.

 Pisces Aries Taurus B1875 J2000 RA dec Longitude numbers plot image ` 25.0 ` ` 10.381 ` ` 28.687 ` numbers plot image ` 49.25 ` ` 18.181 ` ` 53.417 ` numbers plot image ` 88.25 ` ` 23.430 ` ` 90.140 ` numbers plot image ` 118.25 ` ` 20.903 ` ` 117.988 ` numbers plot image ` 138.75 ` ` 15.955 ` ` 138.038 ` numbers plot image ` 172.75 ` ` 3.134 ` ` 173.851 ` numbers plot image ` 213.75 ` ` -13.541 ` ` 217.810 ` numbers plot image ` 237.092 ` ` -20.0 ` ` 241.047 ` numbers plot image ` 244.0 ` ` -21.289 ` ` 247.638 ` numbers plot image ` 264.0 ` ` -23.324 ` ` 266.238 ` numbers plot image ` 300.0 ` ` -20.580 ` ` 299.656 ` numbers plot image ` 328.0 ` ` -12.941 ` ` 327.488 ` numbers plot image ` 350.723 ` ` -4.0 ` ` 351.650 ` numbers plot image

Strasbourg: constellation boundaries
Jim Kaler: constellations

 Last Revised: 2015 February 27th