Constellation of Virgo

Spica: Sixteenth brightest star in the heavens at magnitude 0.98 and a spectroscopic binary. Both components are hot “B” type giants and the system is 262 light years from us. Porrima: Very famous double star with virtually equal yellow-white 3rd magnitude components. Unfortunately the two stars are currently at the closest point to each other (“periastron”) in their 170 year orbit and therefore will not be easily split by Earth-bound telescopes for another few years.

The Virgo Galaxy Cluster: The closest “supercluster” of galaxies to Earth, containing several thousand members, of which several dozen are visible in modest telescopes. The above diagram shows just the eleven catalogued by Charles Messier within Virgo itself .A number of the other prominent galaxies in the cluster lie north of the border of Virgo with Coma Berenices.The star chart image is of that drawn by Messier, cropped from a larger chart he published with his observations of the comet of 1779 (all 16 Messier objects are marked in this drawing).

                                   The Virgo Cluster

               Messier's star chart

                   M104, The Sombrero Galaxy

Sombrero Galaxy M104: Considered to be one of the outlying members of the Virgo cluster, M104 lies on Virgo’s southern border with the constellation of Corvus. It is one of the most recognisable galaxies because of its prominent dust lane (although this does not show up well in amateur telescopes). It is also famous for being one of the first galaxies shown to have a large red-shift. It is receding from us at 700 miles per second. When in the 1920’s many other galaxies were also shown to have large red-shifts, this led Edwin Hubble to the discovery of the expansion of the Universe.

Furthest Backyard Object: What is the most distant object that can be seen through a typical amateur telescope (say 200mm – 250mm aperture)? The thirteenth magnitude quasar 3C 273 in Virgo has a fair claim at around two billion light years – 50 times further away than the Virgo cluster. Quasars were very mysterious objects when they were discovered in the 1960’s. It is now thought that their enormous luminosities are due to active super-massive black holes in their centres.