The Virgo Cluster
Virgo, the second largest constellation and the sixth of the zodiacal constellations can be found high in the northern sky in the month of April. Virgo measures more than 30 degrees (three fist widths) in both directions and lies on either side of the equator.
In mythology Virgo stood for several young innocent maidens, one was the goddess of harvest with Spica (alpha Virginis) representing the ear of wheat in the goddesses hand. In another myth she was Justina or Astraea the goddess of justice where she weighed truth and innocence on the scales of Libra lying to the east.
Spica – α Virginis the blue/white star marking the south-eastern corner of the constellation lies almost on the ecliptic, and it is the brightest star in the constellation at magnitude 1.0 . It is a spectroscopic binary which means that they are not visually separable and are determined to be two stars due to the observation of their light spectrum.
γ (gamma) Vir is a 2.8 mag. double star, the pair of yellow – white stars are 3.5 mag. each and orbit each other every 169 years. These stars were at their closest in 2005 and now are moving apart allowing the observer to distinguish their profiles with an average telescope. By 2010 a 100mm scope will split them.
δ (delta) Vir is a 3.4 mag red giant
ε (epsilon) Vir is a 2.8 mag yellow giant
ζ (zeta) Vir is 3.4 mag
Alpha, gamma, zeta and delta form the distinct pattern of Virgo in the northern sky.
Virgo is the galaxy observer’s paradise – it contains the nearest galaxy cluster to us at 40 – 50 million ly away. The Virgo Cluster of Galaxies located in the north-western sector of the constellation, North West of Epsilon Vir. contains around 3000 members. The cluster spreads into the neighbouring constellation Coma Berenices. A few dozen can be seen with 150mm apertures as small hazy patches of light. With 78mm apertures some of the galaxies can be seen, however they are very small fuzzy streaks. The region is so rich in galaxies it is sometimes difficult to determine which you are observing. It is best to use your star charts and search for pairs or groups of galaxies and from these you will be able to identify more.
M49 (NGC 4472) magnitude 8.4 elliptical galaxy is one of the brightest galaxies in the cluster – visible in 78mm as a round glow. It is slightly bigger and brighter than M87. North of M49 approximately 20 galaxies of 10 mag. or brighter can be found in a 10 degree area.
M87 (NGC 4486, above) giant elliptical galaxy one of the largest in the cluster, about 1 magnitude greater than M84 / M86. A jet of gas streams from this galaxy thought to be from energetic gas swirling around a black hole. The jet is 5000 light years long and emits an eerie blue light from its spiral.
A group of eight galaxies in the Virgo Cluster extending into Coma Berenices is known as the Markarian’s Chain (see photo on map above – note this photo taken in the northern hemisphere is upside down to how we see it ). This is probably the most photographed region of the Virgo Cluster. It is named after a Russian astrophysicist Benjamin E. Markarian. The 8 members are M84, M86, NGC 4435, 4438, 4458, 4461 and 4473 & 4477 in Coma Ber.
M84 (NGC 4374) mag 9.3 and M86 (NGC 4406) slightly, larger but slightly dimmer than M84 at mag 9.2 form an equilateral triangle with NGC 4388 to the south. In the centre of the triangle is the faint NGC 4387. In photos this group resembles a funny face. East of M86 lying almost in the centre of the Markarian Chain is the pair of galaxies “The Eyes” NGC 4438 – mag 10.1& NGC4435 –mag 10.9. These galaxies were all visible in the same field of view with the C8 (200mm) using the 27mm Panoptic eyepiece with a 68◦ field of view at 75 x magnification and a 17mm Nagler with 82◦ field of view at 119 x magnification. They were all visible with my 78mm Takahashi except the central N4387. I could get the eyes and M86 in one field but had to move these out of view to see the other galaxies and they were all very faint streaks with 78mm, more impressive in the C8.
M104 The Sombrero Galaxy is near the border of Corvus. At mag. 8 it is one of the brightest Messier galaxies and is easily found by locating delta Corvi, then using your binoculars or finder scope, find a triangle of stars below this which points down to a close bar of three stars; M104 is just below this. In the 78mm refractor it appears as a faint fuzzy streak. With the 20mm Celestron a dark lane is visible across the centre of the spiral galaxy.
The Siamese Twins, mag 10.8, NGC 4567 & 4568, is another pair to locate, you will need at least a 200mm (8 inch) telescope. They are east of the Markarian Chain.
Sources: Collins Stars & Planets, Hartung’s Astronomical Objects for Southern Telescopes by Malin & Frew 1995 and The Southern Sky Guide second edition by David Ellyard & Wil Tirion.