Who would have thought it? In the middle of galaxy season, there is a seldom observed small asterism that has been called “a stellar diamond in Virgo”. Jaakko Saloranta, an observer from Finland states that “what makes this asterism curious and stand out is the diamond or square-shape and its tiny size (50″).” The separation between the stars is – on average – only 30″. Good seeing conditions and higher magnification is required to resolve the four main components into individual stars. Seeing the 5th star on a less than average night, may require a telescope with a larger aperture than the typical backyard telescope.
As reported in the May 1993 issue of Sky and Telescope Magazine, page 110, Noah Brosch of the Tel Aviv University, Israel, discusses his investigation of a newly discovered asterism in the December 1991 Monthly Notices of the Royal Astronomical Society. In summary he states that this is a system of five stars arranged in the form of a diamond. The stars have similar spectral types and radial velocities, indicating that the system is probably an evaporating small cluster in the Galactic halo.
Roger Ivester, an observer from North Carolina, said that on his first observation in his 10-inch Newtonian that he was surprised by how small the diamond appeared. Sue French, an observer from New York, states that with her 4-inch (105mm/610mm) the northern most star was easy but the other three are very faint at 122x. With her 10-inch Newtonian she could see all five stars at 213x. This year at the Winter Star Party, she could see all five stars with her 5-inch (130mm/819mm APO) at 164x. Several other people have seen all five stars with larger instruments.
Have I got you interested yet? This is a great challenge object that is a very nice break in the middle of galaxy season. With small telescopes this asterism will require dark skies with good seeing and good transparency. To help you I have prepared a sketch of this asterism from available information. It is located between Gamma (Porrima) and Eta (Zaniah) Virginis at R.A. = 12h 32.8m and Dec. = -00d 42m. The brightest star in the group is the 10.7 magnitude star TYC 4948-53-1.
and below is a photograph of the Diamond by Don Olive. This is , of course, not to be taken for the Great Diamond of Virgo. The four stars that form the Diamond of Virgo are Cor Caroli (in Canes Venatici), Denebola (in Leo), Spica (in Virgo), and Arcturus (in Bootes).