COTM: Virgo

Ross Gould

Virgo is one of the zodiacal constellations, the figure as usually drawn with a sheaf of wheat representing an ancient fertility goddess far pre-dating the Ceres of the Greeks – its origins lost in the pre-literate religions of the ancient Middle East. For the deep-sky observer the main interest is in the multitudes of galaxies found here. There are also many double stars, including the showpiece Gamma Virginis, and a globular cluster.

Doubles

Gamma Virginis (1241.7, -0127) is a fine bright yellow binary with a very elongated orbit. It is presently closing, and will be very difficult until the end of the present decade. Hartung and other older books quote a period of 171 years, but a revised orbit by Heintz in 1990 suggests that the orbital period is slightly shorter (168.7 years) than previously calculated.

This was only the second binary to have an orbit calculated (in this case, by John Herschel in 1833). The ephemeris here is from Heintz’s orbit (separation and PA):

2004  0.59”  209
2005  0.37”  154
2006  0.49”  080
2007  0.78”  050
2008  1.04”  036 

As can be seen, the PA changes very rapidly near minimum separation, and the pair widens quickly after 2006. At present it forms a test of seeing as well as optics, given the bright components (both mag 3.5).

When I first observed Gamma Vir forty years ago it was an easy pair in a 6-inch Newtonian, at nearly 5” separation; in 1993 at 2.35” it was a neat pair in a 7-inch refractor at 100x. At its closest in 1836 John Herschel found the pair unresolvable in his 18-inch reflector.

Among (many) other doubles of interest are:

Theta Vir (1309.9, -0532) stars of mags 4.4 and 9.4 at 7” make an easy pair – there is also a wide 10th mag companion. The main pair is white and yellow.

54 Vir (1313.4, -1850) a slightly uneven pair of 7th mag yellowish stars, at an easy 5” separation.

84 Vir (1343.1, +0332) The primary is orange, its less bright companion pale yellow – mags are 5.5 and 7.9 at a not too hard 3”. A nice double in steady seeing.

Galaxies

There are so many galaxies in Virgo within reach of moderate apertures – even Messier lists 11 - that no more than a small sample can be given here. Virgo is at the heart of the Coma-Virgo supercluster, and one could spend many nights exploring these regions without exhausting the accessible objects. In the May 2002 Southern Cross Jenni Kay described 20 galaxies in the M61 area alone, as seen with an 8-inch telescope. That is only one small part of this region, and limited by the 8-inch aperture – a bigger scope greatly increases the riches available.

My choice of the best showpiece galaxy in Virgo is M104 (1240.0, -1147), the ‘Sombrero’ galaxy. Small telescopes show the sombrero effect, which is simply the major part of the galaxy seen as a ‘hat’ - but a little more aperture brings the fainter side of the galaxy into view, providing a clear view of the dust lane cutting across the near edge-on galaxy. I’ve found both sections of galaxy visible with a 7-inch refractor, the excellent contrast of the optics showing the effect well on moonless nights despite a suburban location.

Among the many other galaxies, the following will prove of interest. I have avoided here the giant elliptical galaxies, impressive in AAT or Hubble photos, but featureless blobs in the usual backyard telescope.

One of the concentrated fields of galaxies is the group NGC 4270-73-81 (etc). The DSS photo shows the group nicely – the brighter members are visible in a 20cm scope. Hartung mentions 5 galaxies here in a 12’ field, the brightest NGC 4281. Positions are: NGC 4270 (1219.8, +0528); NGC 4273 (1219.9, +0521); NGC 4281 (1220.4, +0523).

NGC 4303, M61, (1221.9, +0428) is a bright face-on spiral – 18cm shows a bright nucleus with an uneven haze surrounding it. Large amateur scopes (16-inch and up) reportedly make the spiral arms visible from dark sites.

NGC 4535 (1234.3, +0812) is another face-on spiral – a faint diffuse patch with brighter centre in an 18cm scope, the multi-armed spiral is striking in photographs. Another example of the limitations of visual observing…

NGC 4536 (1234.5, +0211) is a faint diffuse haze in smaller scopes, though showing something of its true form in larger scopes.

NGC 5574-76-77 (5576 is at 1421.2, +0316): three galaxies in a small field, though 25-30cm may be required to make them easy.

NGC 5746 (1444.9, +0157) is an easy edge-on spiral with a dust lane: the galaxy is easy with 18cm, showing a central bulge, but the dust lane probably needs at least twice this aperture.

NGC 5774-75 (5775 is at 1454.0, +0333). Two contrasting galaxies, both visible with 18cm, but the face-on spiral 5774 is only a very faint blur.

Globular Cluster

NGC 5634 (1429.6, -0559). A fairly easy but small and (in 18cm) unresolved globular. Hartung claims some resolution into stars with 30cm, but other observers find it only granular with 14-18-inch scopes.

See also May 1997