One of the best challenges of a beginning Deep Sky observer and the completion of the Messier List is the conquest of the Virgo Cluster of galaxies.
First we'll discuss the historical perspective behind the discovery and composition of the Virgo Cluster and then move on to specific Tips on Observing the Virgo Cluster.
This giant agglomeration of galaxies is the nearest big cluster of galaxies, the largest proven structure in our intergalactic neighborhood, and the most remote cosmic objects with a physical connection to our own small group of galaxies, the Local Group, including our Milky Way galaxy. This structure is another discovery by Charles Messier, who noted behind his entry for M91 (here quoted from Kenneth Glyn Jones' book):
Together with his later entries, 98, 99, and 100, Messier had cataloged 16 members of the Virgo cluster which he viewed as a 'cluster of nebulae'. Pierre Méchain, in a letter of 1783, stated that he had seen even more "Nebulae" in this region which "Messier had not seen;" unfortunately, no records are known indicating which galaxies this may have been.
The image shows the central portion of the Virgo Cluster of Galaxies, and is centered on the giant elliptical galaxy M87 which is considered to be the dominant galaxy of the whole giant cluster, situated close to its physical center. The two bright galaxies on the right (west) are (right-to-left) M84 and M86; starting from these two, a chain of galaxies ("Markarian's chain") stretches well to the upper (northern) middle of our image (and beyond, well to M88 which is slightly outside above the sky area photographed our image). The appealing group around these two giant lenticulars is described with M84, and in our collection of images with M84 and M86; we also have images of M87 together with Markarian's chain around M84 and M86. To the left (east) of M87, the considerably bright elliptical (type E0) M89 occurs (on roughly the same declination as M87), above it and slightly more left is the inclined and conspicuous spiral M90, while below (south) and left of M89 there is M58, sitting just on the edge of the image.
The Virgo Cluster with its some 2000 member galaxies dominates our intergalactic neighborhood, as it represents the physical center of our Local Supercluster (also called Virgo or Coma-Virgo Supercluster), and influences all the galaxies and galaxy groups by the gravitational attraction of its enormous mass. It has slowed down the escape velocities (due to cosmic expansion, the `Hubble effect') of all the galaxies and galaxy groups around it, thus causing an effective matter flow towards itself (the so-called Virgo-centric flow). Eventually many of these galaxies have fallen, or will fall in the future, into this giant cluster which will increase in size due to this effect. Our Local Group has experienced a speed-up of 100 to 400 km/sec towards the Virgo cluster. Current data on the mass and velocity of the Virgo cluster indicate that the Local Group is probably not off far enough to escape, so that its recession from Virgo will probably be halted at one time, and then it will fall and merge into, or be eaten by the cluster.
Because of the Virgo Cluster's enormous mass, its strong gravity accelerates the member galaxies to considerably high peculiar velocities, up to over 1500 km/sec, with respect to the cluster's center of mass. Investigations over the past decades have revealed a quite complex dynamic structure of this huge irregular aggregate of galaxies. The Virgo cluster is close enough that some of its galaxies, which happen to move fast through the cluster in our direction, exhibit the highest blue-shifts (instead of cosmological redshifts) measured for any galaxies, i.e. are moving toward us: The record stands for IC 3258, which is approaching us at 517 km/sec. As the cluster is receding from us at about 1,100 km/sec, this galaxy must move with over 1,600 km/sec through the Virgo Cluster's central region. Analogously, those galaxies which happen to move fastest away from us through the cluster, are receding at more than double redshift than the cluster's center of mass: The record is held by NGC 4388 at 2535 km/sec, so that this galaxy moves peculiarly in the direction away from us at over 1,400 km/sec.
You will need a good plan to wind your way through the Virgo Cluster, comprised of 14 galaxies in Virgo and Coma Berenices. I recommend you follow the order suggested in the "Marathon Order" as listed on the sheet you can find Here. The path starts in the eastern edge at Epsilon Virginis and goes toward the west rather than following the west to east, right ascension order from the list works well with most of the other objects. If you get halfway through and get lost, don't panic. Start over again and the second time you will be able to quickly get back to the last galaxy you had observed...
By: "Tony Cecce, Corning, NY"
Successfully navigating the Virgo cluster is the biggest challenge in the Messier Catalogue, and is affectionately known as "Heartbreak Ridge" to marathoners. What makes the Virgo cluster such a challenge is the closeness of the Messier objects to each other, and the large number of other galaxies in this region. It is easy to become lost among the galaxies, and not be able to tell which one you are looking at. Here are several tips that can be of use as you navigate your way through the cluster.
- Get a good chart of the region that shows not only the M objects, but also the brighter NGC galaxies. You should also have pictures of the objects in the region to help in confirmation of a sighting.
- Use low power while searching. When you find an object you can switch to higher powers to see more detail.
- Avoid large aperture scopes. Small telescopes 6"-8" in size make finding the M-objects easier. Large scopes will show many of the other faint galaxies and may help you become disoriented. Same is true for sky darkness. Minimal light pollution will also help to "filter out" the dimmer galaxies from the brighter Messier objects. In my moderately light polluted back yard with an 8" scope I can find the Messier objects easily, but can barely see the other galaxies. Of course to really enjoy and get the most out of any galaxy you want the largest scope and darkest skies you can find.
- Plot your paths through the cluster, including a "home base". Your home base should be an easily recognizable M-object or field in the cluster. This will be the starting point for any excursions you plan, and a place to return to should you become lost. I use M84, M86 as my home base. I can find this pair of galaxies easily by pointing my accurately aligned telrad on the midpoint of a straight line from Denebola (Beta Leonis) to Vindemiatrix (Epsilon Virginis). This matched pair of small fuzzy balls will both be within a low power field of view every time I do this. I've heard of other people using M87 as their home reference because of it's brightness.
The paths I like to use are:
M84, M86 -> M87 -> M89, M90 -> M91 -> M88
|----> M87 -> M89 -> M58 -> M59, M60
|----> M99 -> M98 -> M100
- As you move from an identified object in search of a new object keep track of how far you have traveled. At low power the most you should have to move between objects is 3 or 4 fields of view. If you go much farther than that go back to your last object or all the way back to home.
- Have patience and keep trying. Getting to know this area of sky is very rewarding. Under dark skies and with a large scope I can easily get seven galaxies into the same field of view. An amazing sight to behold.
- Remember, you are looking for light that left it's source about 70 million years ago. Most of these objects at low power are not much more than dim, fuzzy, out of focus looking stars. Allow your eyes to become fully dark adapted and take your time looking at each field. When done with this challenge be sure to swing over to M3 or M13 to let your photon starved retinas feast on a real meal.
Practice and patience payoff in the Virgo Cluster. The suggested observing order for objects in Coma Berenices and Virgo is as follows:
More Observing Tips
Rich Neuschaefer at firstname.lastname@example.org