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Virgo Galaxy Cluster

Virgo Cluster, Virgo I, Virgo Galaxy Cluster

RA: 12h 26m 32.1s
Dec: +12° 43′ 23″

Con: Virgo
Ch: MSA:725, U2:193, SA:13

Ref: SIMBAD

(reference key)

Type: galaxy cluster

Mag: B=?, V=?

Size: ?
PA: ?

Published comments

Photo index

by Jim Lucyk: Sky & Tel. 6/82 p550, Sky & Tel. 1/88 p16, Astronomy mag. 11/79 p19, Deep Sky #3 Su83 p31, Burnhams V3 p2077

de Vaucouleurs, G. (1975)

de Vaucouleurs, G. (1975) Nearby groups of galaxies. In: Kuiper, G. (ed) Stars and Stellar Systems. Volume 9: Galaxies and the Universe. Chapter 14, p557.

Modern observations

Mark Wagner

Date: Tue, 30 May 1995 11:15:26 -0700 (PDT) From: "mgw@resource-intl.com

Subject: Observing: May 28-29, 1995. To: Astronomy List [astro@mindspring.com]

Humility and Illumination... the Virgo Cluster.

By Mark Wagner

Sunday May 28, Dean Linebarger, Alan Nelms and I took advantage of a clear and warm night at Fremont Peak to work the Virgo portion of the Herschel 400 list on the 30" Challenger telescope.

As the Earth's shadow rose in the east, and the breeze began to subside, the sky revealed very steady and transparent conditions. Having been at Grant Ranch the night before, we could tell that the fog settling in over the city lights would provide a significantly darker sky.

Alan brought a 75MHz laptop loaded with The Sky. With a fast processor, the program was an invaluable observing aid. We decided on the 35mm Panoptic for wide-field, and a 20mm Nagler for detail.

Our first objects were easy targets. NGC4030, an elongated dusty galaxy some 4.5" x 3.3" shown clearly at mag 12.00, with marvelous detail. We all felt this would be an exciting and productive evening. Next on to NGC4179, a mag 10.90 dusty edge-on 4.0" x 1.1". Other IC and NGC's were found close to these two bright Herschels. Both galaxies were mostly alone, and in easily identifiable fields near bright guide stars.

Things changed. We entered a dense portion of the Virgo Cluster. I found that the 30" is a great for sucking up phaint-photons, but also complicates the field of view! Arguments ensued over whether we were in the correct field. We all used different methods of naked-eye star-hopping, finding hard won success. Many targets were packed closely with other galaxies, distant sardines with no close-by guide stars. The Sky began paid dividends now, zooming in and out, check relative sizes and position angles. When unsure of our eyepiece view, we'd move to nearby clusters to verify on computer. One field held nine galaxies without trying. Dense clusters were unavoidable. Messier Marathoners know Virgo is time consuming and difficult. Hershel's list multiplies the challenge. Too many galaxies... I began longing for sparser fields of my 10" scope!

The Hershel highlight was NGC4216, a 10th mag edge-on with bright core at 7.3" x 1.7". The same 35mm field held NGC4206 and NGC4222, edge-ons at mag 12.09 10" x 5.3" and mag 14 3.2" x 0.6". All lay in nearly the same position angle.

Crowded fields, calculations, star-hopping and verification became wearing. We'd barely dented the list as Virgo began to set. The wet and cloudy spring succeeded in moving most of Virgo to my 1996 calendar.

To relax, we looked at highlights. M51, M13, M22, M17, Veil, Dumbell, Lagoon, Barnard 86. The Eagle's with dark areas shown very clearly, and the Triffid's three very clearly defined dark lanes were outstanding.

Just past 2 a.m., facing north taling with Dean at the eyepiece, the entire observatory was illuminated with halogen-like bright white light.

Startled, we immediately looked to locate the source when I saw the bright blue-green trail of a meteor fading, extending from north of Deneb into Cepheus. Never have I seen a meteor cast shadows or have a such brilliance. It was an unforgettable sight.

By 3:20 fatigue set in. We had a very good observing evening. After a fast pack up we headed home. I closed my eyes to sleep as the dawn was breaking.

Todd Slisher

Date: Tue, 30 May 95 17:50:23 EDT

From: Todd Slisher [D700071@univscvm.csd.scarolina.edu]

Subject: Re: Observing...

To: astro@FLUX.MINDSPRING.COM

Mark,

I too challenged the Virgo Cluster back on May 21. I had a beautiful night to work with, with a limiting magnitude of around 6-6.1. Although not trying for the Herschel 400, I was on a quest of my own, trying to make sure I observed and sketched all 110 M objects. Working with a 8" SCT, I managed to sketch most of the Messiers and observed about 20 of the NGCs. Quite a successful night, especially from SC.

One thing that helped immensely was a chart published in Sky & Tel in the April or May, 1994 issue. It plots stars to 11.0 mag and galaxies to 12.5 mag. It also contains a route for star-hopping and several photos of particularly dense regions. I agree with you that the density of galaxies in this region, coupled with the lack of bright stars makes it a challenge, but if anyone else out there is thinking of going after the Virgo cluster I highly recommend they get a copy of this chart.

Todd Slisher Columbia, SC

S. Waldee

Observing report:

Dipping An Eyepiece Into the Coma & Virgo Clusters: A Guide to Finding & Observing the Messier Galaxies, by. S. Waldee

A recent post to the newsgroup sci.astro.amateur from a beginning observer with a 4.5" aperture Newtonian telescope complained of the frustration of sweeping through the highly-touted Virgo cluster of galaxies and seeing nothing but 'specks' and stars.

As a amateur observer who has practiced regularly with a good- sized telescope each new moon for at least the past 22 years, this writer can sympathize. In fact, it has been about 5 years since our last systematic survey of the Coma - Virgo galaxy cluster, because the effort required for acquisition and identification of the numerous galaxies -- bright though many of them may be -- is so much like WORK! Yet nothing this satisfying can be easily gained.

What Is the Coma/Virgo Galaxy Cluster?

"We have noted the tendency of stars to associate with companions and to form multiple systems of various sizes; we have also observed how all these star systems are bound together in great conglomerates called galaxies. In an apparently universal plan characterized by stellar systems of ever increasing dimensions, galaxies also combine gravitationally to form their own supersystems; each of these may contain anywhere from a dozen to thousands of galactic members," write Motz and Nathanson in their work The Constellations: An Enthusiast's Guide to the Night Sky.

The ancient constellation Coma Berenices (Berenice's Hair) was first charted by the great Renaissance visual observer Tycho Brahe. The faint stars (barely naked- eye- visible in a near- urban sky) probably reminded early skywatchers of long, flowing tresses: indeed, the Coma Star Cluster (Melotte 111) is a naked- eye 5- degree dense nebular patch that resolves into a myriad of sparklers with the most modest optical aid. Had Tycho access to a telescope like Galileo's, the 80 stars of the cluster would have astonished him with their richness. However, modern observers are admonished to use their binoculars, finderscope, or widest possible richfield instrument to appreciate the clustering effect, which is lost at narrower fields and higher magnifications.

There are two galaxy clusters in Coma. According to Motz and Nathanson, the rich cluster in the northeast corner of the constellation, which extends into adjacent Virgo, is far from our Local Group of galaxies. Our former estimate of 400 million light years recently has been pushed farther by means of CCD imagery and redshift analysis, to a distantly- receding 5 to 9 billion light years! Truly, a telescope is a time- machine as it peers halfway across the known distance of the universe to this vast territory. The galaxies in this group are much fainter -- and invisible to small urban telescopes -- than the relatively nearby Coma-Virgo cluster, extending mostly from northeastern Virgo into Coma at a distance now determined to be from 42 million to 78 million light years, depending on whose authoritative calculation is accepted. 2,500 or more galaxies are found in this region -- the nearest galaxy cluster from our Local Group -- having a diameter of 120 square degrees and irregular distribution without any central condensation of galaxies. Charles Messier found 16 galaxies ('nebulae') in the Coma- Virgo cluster: according to Robert Burnham, Jr. (writing over 20 years ago in his Celestial Handbook) there are probably some 100 galaxies in this cluster that are within reach of an 8-inch aperture scope! One assumes that today's amateur observers have far exceeded this number, especially with CCD imaging capabilities.

According to its absolute magnitude of -21, M-100 is the brightest of the galaxies in the group; its visual magnitude rating is 9.4, which is very slightly fainter than the bright pair M-84, 86 (at 9.3 and 9.2, respectively.) The gigantic elliptical galaxy M-87 (now believed to contain evidence of a black hole) is nearly as brilliant as M-100; yet it is visually dimmer than M-84 & 86.

Burnham succinctly describes the experience of exploring this region by eye: "In small telescopes none of the members of this galaxy cluster are visually impressive; they appear mainly as pale little patches of light, round, elongated, and irregular; even the brightest members are not brilliant or striking objects." As usual, his recommendations for minimum scope aperture are somewhat conservative, suggesting a 6" or larger instrument. Yet John Mallas used a 4" achromat refractor, more efficient than Charles Messier's discovery instrument, for the drawings and eyepiece descriptions in the Mallas & Kreimer book The Messier Album from Sky Publishing.

In most instances, the sharp-eyed Mallas discerned fine shadings and details, even in the elliptical galaxies of the cluster, though this author finds his renderings to be peculiarly stylized and generally unreliable. Rather than showing 'closeups' of high contrast (per Mallas), this author prefers to present eyepiece drawings that attempt to duplicate an actual ocular field of view at low to moderate magnifications. In such views, the image scale and palette of color and shading used to replicate the galaxies will be limited in size and contrast range, evoking the "pale little patches" as they are generally seen. However, the Mallas book is an invaluable reference work with excellent photos by Kreimer, convenient data and descriptions, and Owen Gingerich's superb historical essay on Messier and his "comet-like" object discoveries.

Finding the Virgo-Coma Galaxy Cluster

On the helpful series of naked- eye finder charts by Brent Watson of Sky Spot (see references below for purchasing information), the Virgo cluster is described as being "packed with more galaxies than any other area. It is so congested that differentiating between galaxies is difficult without a means of telling them apart...the best way to find this celestial gathering is to look at the midpoint of a line drawn between [Vindemiatrix in Virgo and Denebola in Leo]. M84 and m86 will be the brightest galaxies seen in this field." If very accurately- calibrated telescope setting circles are not available for hunting down the galaxies, we recommend using an upright, corrected finderscope (using a Porro prism so that the views agree precisely with a star catalog) and then carefully "hopping" using the detailed charts in the Uranometria atlas, perhaps augmented with wider- field constellation views in Tirion's Bright Star Atlas, both available from Willman-Bell Publishing. In addition, an excellent WWW site is available with information and photographs of these objects: The SEDS Messier Database. For a series of on- line deep- sky charts and constellation information, consult The Hawaiian Astronomical Society and its Deep-Sky Atlas.

We of course cannot replicate the copyright chart by Brent Watson, so instead the image above was prepared from a chart of the region produced by the software program GUIDE 3.0 CD-ROM, with some additions and interpolations to clarify the labelling. As you can see, 47-Epsilon Virginis (Vindemiatrix) is on the left: a 2.8 magnitude bright star, spectral type K0 (hot, bluish color); 18 degrees away (a little over 2 hours earlier in Right Ascension) is 94-Beta Leonis (Denebola), an A2 type (cooler, reddish) star of magnitude 2.1. Along the line between the stars are arrayed many of the galaxies of the Coma- Virgo cluster, of which the Messier objects are just a tiny handful.

Of course, there are numerous galaxies discovered after the time of Messier, by the Herschels and later visual observers, that may be scrutinized in this region. For the purposes of this article, however, we shall concentrate on the "nebular specks" discovered by Messier in the late 1770s and early 1780s, and include also the famous "Siamese Twins" galaxies (NGC-4567 & 4568) that should pose no special difficulty once the somewhat brighter Messier objects have been identified.

Sweeping Up the Galaxies: The First Three

Is there a "best way" to observe the grouping? Probably not. Burnham suggests starting with the crowded region of M-84 & 86; however, this author was working against the clock, as the constellations sank into the western horizon, and so began east of Denebola with M-98, M-99, and M-100. First, the finder charts for the grouping. M-98 is about two and a half degrees from M-100, so the observer will sweep more than 1 typical eyepiece field to maneuver among these 3 galaxies.

In the field of view for galaxy M-100, observers with sufficient telescope light-gathering and dark skies may be able to detect the galaxy NGC-4312, an 11.7- magnitude spiral of dimensions 3.8 x 0.9 arcminutes. Though its rated surface brightness is almost exactly that of M-100, the galaxy is so much smaller in angular diameter that it is rated at 2.4 magnitudes dimmer visually, and thus appears only a fraction of the brightness of M-100 (the actual difference depending greatly on the scope aperture and observer sensitivity.) Luginbuhl and Skiff (in OBSERVING HANDBOOK AND CATALOGUE OF DEEP-SKY OBJECTS) find that it is "faintly visible" in a 6-inch aperture scope.

M-98: Dreyer Summary (NGC): Bright, Very Large, Very Much Extended Along Position Angle 152 Degrees; Very Suddenly Very Much Brighter Toward the Middle. John Sanford description: "...a large spiral seen almost edge- on, about 3 by 9 arcminutes in size and of 10th magnitude. It is easily located about a half a degree west of the star 6 Comae." In our notes for the eyepiece view at 85x, we saw "an edge-on galaxy with nuclear region slightly offcenter toward the East, especially noticeable at 220x."

M-99: Dreyer Summary (NGC): Very Remarkable. Bright, Large, Round, Gradually Brighter in the Middle, Mottled - Not Resolved. 3-Branched Spiral. John Sanford description: "...a wide-open, face-on with two prominent arms which become evident in a 16-inch (40-cm) telescope." In our 8-inch scope's eyepiece view using 125x, which provided a true field of 30 arcminutes, we saw "a hint of spiral arm shape with averted vision."

M-100: Dreyer Summary (NGC): Very Remarkable. Pretty Faint, Very Large, Round. Very Gradually, Then Pretty Suddenly Brighter Toward the Middle, Mottled Nucleus. 2-Branched Spiral. John Sanford description: "M100 (NGC 4321) has been called the brightest galaxy in the Virgo cluster. It appears as a large haze 6.9 by 6.2 arcminutes across, with a bright nucleus. In 14-inch (35-cm) or larger aperture telescopes, two major arms are seen wrapped around the nucleus." Our notes for the above eyepiece drawing recorded of M-100 that "at 125x a bright nucleus was detected in an uneven disk; with wider field, NGC 4312 was clearly seen. Galaxy NGC 4328 [not shown in drawing] was faintly visible 6 arcmin from M-100, using averted vision, at a magnification of 220x." We did not record spotting faint galaxy NGC 4322, 5 arcminutes to the north of M-100.

M-85: Elliptical or Spiral Galaxy? Described as an "elliptical" galaxy (a type, according Edwin Hubble's classification system, that features a more amorphous shape than a spiral galaxy like our Milky Way system) in the Mallas & Kreimer book The Messier Album and in the Sky Catalogue 2000.0 (which designates it as an Ep: only somewhat flattened), M-85 is categorized as being an SA(s)0+ pec in The Deep-Sky Field Guide to Uranometria 2000.0: a peculiar tightly-wound spiral featuring an extremely bright nucleus. The late John Mallas' drawing on p. 160 of his book captures an uneven shape that differs from the Kreimer photograph on the facing page. According to Luginbuhl & Skiff, a 12" aperture scope shows it to be "very well concentrated, appearing like an unresolved globular cluster." Our eyepiece drawing and notes about the galaxy will be included below, with the bright pair M-84 and M-86.

The Bright Pair M-84 & M-86 and Giant M-87 Brent Watson's naked- eye "Telrad" (tm) charts aptly describe this beautiful pair of notable Messier elliptical galaxies in the Virgo cluster as "bright, nearly round luminous spots." Mallas finds "this beautiful sight an easy target for the 4-inch and is even visible in the refractor's 10x 40mm finder" (though it was only just barely detected in the larger finder of this author's scope.)

M-86, according to Mallas, "drops off [in brightness] from the center to a rather sharp edge"; he depicts a bland-looking oval shape in his drawing.

M-84: Dreyer Summary (NGC): Very Bright, Pretty Large, Round, Pretty Suddenly Bright Nucleus; Mottled - Not Resolved. John Sanford description: "M84 and M86 are almost twin elliptical galaxies located at the heart or nucleus of the Virgo Cluster [the great cluster of galaxies in Virgo known by Hubble's term "The Realm of the Nebulae" -- today, galaxies -- for its rich assortment of such objects]. M84 is the westernmost of the two, and is a round, bright diffuse object, rising strongly to the center." The original code used by Dreyer in the 1888 New General Catalog for this object reads: vB, pL, R, psbM, r; = M84 It should be pointed out in our parsing and translation of Dr. Dreyer's code, we regard "r" to be a designation for 'resolvable or mottled but not actually resolved'; during the pre-photographic era of visual observation, many objects that were indistinctly seen were believed to be eventually resolvable into discrete shapes or clusters; most were not resolved, as they were too far away for Earth-based instruments to be able to clearly detect any stellar components. Our notes for the 85x view with a 45' true field record that "four galaxies were clearly seen in this one field." We drew M-84 as being a bit brighter and more conspicuous than M-86, which tends to confirm most descriptions.

M-85: Dreyer Summary (NGC): Very Bright, Pretty Large, Round, Bright Middle, Star North Preceding. John Sanford reports in OBSERVING THE CONSTELLATIONS that "about 30 galaxies in the Coma cluster (adjoining the Virgo galactic realm) may be seen in an 8-inch telescope. M85 is a bright elliptical which telescopically outshines M88, M99, M91, and M100 in the same region." Our note for the drawing made with the 8" f5.2 scope recorded that galaxy NGC 4394 -- a spiral seen nearly face-on, shining at 10.9 magnitude at an angular diameter of 3 arcminutes -- "was also seen using 125x and an exit pupil of 1.6 mm."

M-86: Dreyer Summary (NGC): Very Bright, Large, Round, Gradually Brighter in the Middle Toward Nucleus; Mottled - Not Resolved. John Sanford description: "...slightly elliptical, but also has the smooth brightening towards the center typical of ellipticals. M86 has another elliptical companion within its halo, which I estimate to be about 15th magnitude, on the northern side. " In our eyepiece drawing, there was only a slight brightness or size difference recorded between the galaxies M-84 and M-86; the fainter edge-on spiral NGC-4387 (12th magnitude; less than 1 arcminute on its narrow axis) is clearly seen (faintly stretching east/west with a somewhat brighter central nuclear core); NGC-4388 (11th magnitude and a larger 5.7x1.6 arcminutes) is shown in the southwest region of the field, near the top.

M-87: Dreyer Summary (NGC): Very Bright, Very Large, Round, Much Brighter in Middle, 3rd of Three [objects, now known to be galaxies, in the field]. John Sanford description: "The huge ball of stars M87 possesses many more stars than the Andromeda Galaxy, or the Milky Way... Something very strange is going on in the nucleus of M87. It emits strong radio signals (Virgo A). There is a very blue jet of unusual matter emerging from the center...Owners of 16-inch (40-cm) and larger telescopes might want to look for the jet, which is on the northwest side and is 20 arcseconds long and 2 arcseconds wide. A nebular filter might help you see it by suppressing the continuum from the galaxy's stars."

One of the galaxies that are of great interest to current astrophysicists, studies of M-87 and its black hole and erupting jet by the Hubble Space Telescope are breaking new grounds for science. Sadly, typical amateur- sized scopes less than about 15-17" aperture probably cannot reveal the jet of matter that first showed up on early photos taken by Heber Curtis as long ago as around the time of World War I by the Lick Observatory 36- inch Crossley reflector (the present author examined the original Lick Observatory publication in 1990 and found that though the picture was printed with rather low contrast, the object was recognizable as being similar to modern images.) Luginbuhl and Skiff find that despite the fact that M-87 is "one of the brightest galaxies in the Virgo cluster" that "the 45" core is of very high surface brightness; there is no distinct nucleus, but a central stellaring may be discerned with difficulty [in a 10" aperture scope] at high power." Our notes for a view with the 8" f5.2 scope indicate that some trace of this was seen: the galaxy was found to be "roundish, with slightly offcenter nuclear region toward the south. With 220x magnification, an almost stellar brightening observed; was there a faint star a few arcmin to the southwest?"

On reconsidering this description, it would appear that the author spotted NGC-4478, an 11.9 magnitude E2 galaxy, 1.7x1.4 arcminutes diameter, 8 minutes to the southwest of M-87, described as having an "extremely bright center" in the Uranometria; thus, at the image scale of the 8" scope, this probably appeared quite star-like. Thus, it was fun for the author to note his own little "discovery" after the fact, of an object very well known to others but never identified before by the observer. This event illustrates the effectiveness of taking notes while observing, no matter how cursory they may be!

The "jet" of matter from M-87, described by Sanford as being "on the northwest side" and "20 arcseconds long and 2 arcseconds wide" was not seen in the 8" scope (no surprise there!) On 6.6.97, using a 17.5" f4.5 Dobsonian telescope under excellent dark sky conditions, we re- surveyed the galaxy. At high magnification, our colleague Dr. Douglas Hudgins was not able to verify Sanford's description of the jet, but felt rather that Heber Curtis' description was more apt: in 1918 the Lick astronomer found in his photograph that a "curious straight ray" lay in a "gap in the nebulosity..." Hudgins could detect the gap as a generalized darker region in the bright surface, but could not discern the ray. In the 17.5" scope, numerous stellarings were noted: if not actually M-87's globular clusters themselves, perhaps they were the brightenings of regions which contained some of them.

One of the companion galaxies of M-87, NGC-4486A, was apparently spotted by this author in the 8" scope, according to the drawing. The Uranometria description of "Very compact. Star mag. 11.7 plus galaxy 14" seemed borne out by the sketch.

Mallas finds the slightly on-edge spiral galaxy M-88 to be "visually one of the more rewarding galaxies in the Coma-Virgo region. It resembles the Andromeda nebula [galaxy M-31] as depicted on a very small-scale photograph"; in Kreimer's fine image, it does indeed! A "grand" sight in Mallas' 4-inch refractor, he draws it with strange bright interior lumps and an offcenter stellar core. However, Luginbuhl & Skiff find with a 6" scope in a dark sky that "little detail is visible" though the galaxy is bright.

M-88: Dreyer Summary (NGC): Bright, Very Large, Very Much Extended. John Sanford description: "...another compact spiral similar in structure to the Great Galaxy in Andromeda, M31. It appears as a grey-coloured ellipse with no structure apparent until it is seen in very large telescopes. There is a wide double star just to the south and also a closer pair seen against the southern part of the galaxy with larger telescopes." The author's drawing (an inverted, reversed view made while viewing with an 8" Newtonian telescope at moderate power) does not magnify the galaxy to the scale portrayed by Mallas (how that writer - illustrator managed to use effectively such high magnifications with a mere 4 inches of aperture on faint extended galaxies is a great mystery!) The present author's graphical rendering shows a very much smudged ovoid shape, details lost at the scale -- and with the light-gathering -- utilized. There is a slight central density increase, and what appears to be a small brightening to the east of the nucleus.

M-89: Dreyer Summary (NGC): Pretty Bright, Pretty Small, Round, Gradually Much Brighter Toward Middle. The authoritative Alan Dyer reports that M89 resembles M87, but is smaller in diameter. Robert Burnham finds it about 1 magnitude fainter than M87 in the eyepiece; but the generally accepted estimate of integrated visual magnitude is one-half magnitude fainter. The variable nature of this specification indicates that it does not define adequately the surface-brightness of an object. The galaxy was found in a low-power, wide angle field of view as we swept our scope from M-90 down to M-58. Sadly, after concluding our observing sessions for the purpose of this article, the present author discovered that he had neglected to make a specific eyepiece drawing of M-89! So on 6.6.97, using the same telescope, we went back to the Coma-Virgo cluster and produced the drawing above with the 8" f5.2 Newtonian. In his Telrad(tm) charts, Brent Watson aptly describes M-89 as being "like a small fuzzy star". We found that at magnifications from 85x to 220x, a faint halo about 2 or 3 arcminutes in diameter circled a brighter center region of about 1 arcminute, without a sharp boundary leading to the core. A faint star was seen at 125x about 4 arcminutes to the east of the galaxy.

M-90 & M-91 We sweep our telescope a little less than one degree to the east in Right Ascension, and move from M-88 to the large spiral galaxy M-90, appearing in photographs to be oriented slightly narrower in its angle toward the Earth than is M-88. Our finder chart shows several interesting objects worth a dalliance: sadly, we have prepared this AFTER our long 2-night trek through the region, and did not have the opportunity to verify the objects displayed. The double star ADS-8616 (SAO 100195) is shown at the top, to the left (east) of M-91. It looks to be a not-difficult object, stars of 8.1 and 10.2 magnitudes, separated by a fairly wide 7.1 arcseconds. Even the smallest of amateur scopes should not be challenged by this pair. At the top of the chart, galaxy NGC-4548 is just outside the "Aperture" of 1.5 d (90 arcminutes) representing a low-power eyepiece "finding" field. After preparing this chart with the computer program GUIDE 3.0, we had a surprise! That program's compiler and author did not consider Messier 91 to be the "usual suspect", NGC 4548, but instead designated the smaller and fainter galaxy NGC-4571 (inside the "aperture") to be M-91, as given in the original New General Catalog, and so plotted and labelled it. When we were preparing the article, we noted this discrepancy: most modern authorities feel that M-91 is the galaxy shown at the upper right (northwest edge) of the chart. We corrected and relabelled the chart to agree with our own conclusion that M-91 is indeed the bright galaxy shown at the top right (shown in our eyepiece drawing below, with a further explanation of the confusion regarding the galaxy's identity.) The bright spiral galaxy M-90 is shown near the bottom (south) end of the eyepiece field; to the north is the much fainter (and tinier in diameter) IC-3583, which should be relatively easy in scopes larger than 8 inches of aperture.

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