Rho, Omicron & Pi Capricorni -- Multiple Star Systems in Capricornus
A Cow in the Sea Goat
In small telescopes an impressive trio of bright double-stars occurs in the constellation of the
Sea Goat (Capricornus). Designated by their Greek letters of Rho, Pi and Omicron, in
ancient times these three stars were referred to as Bos (Latin for Cow). Today, the name
Bos refers just to the star Rho, but I like the old way of looking at it so all three stars forming this
triangle of naked-eye stars are included in the name.
In the telescope, at low power, Rho appears as a wide double, Omicron as having a
moderate separation and Pi as a tight double. The literature is mixed as to what constitutes
the star system for Rho. It ranges from two stars (eclipsing binary) to six stars including the
wide distinctive pair appearing in the eyepiece. Omicron is a double star, while Pi is a triple
star system, the third star is a spectroscopic binary which is beyond the range of amateur
Unless you have a stable atmosphere the separation of Pi (3.4 arcseconds) might require a
bit more magnification to cleanly split. I was able to see Pi split at the magnification of
37x used for the drawing, but I also used 164x to obtain a less painful view of this pretty double.