Description

Uranometria 2000.0's "Close-up Charts"

• North American Nebula/Pelican Nebula
• Galaxy Cluster Abell 194
• Gamma Cygni Region
• M11/Scutum Star Cloud
• Galaxy Clusters Abell 2197/2199
• Virgo Galaxy Cluster
• Perseus Cluster, Abell 426
• Galaxy Cluster Abell 194
• Galaxy Cluster Abell 779
• Trifid Nebula/Lagoon Nebula
• Galaxy Cluster Abell 262
• Galaxy Clustr Abell 3574
• Galaxy Clusters in Andromeda/Pisces
• Hydra I Cluster, Abell 1060
• Coma Cluster, Abell 1656
• M6, Butterfly Cluster/M7
• Hercules Galaxy Cluster, A 2151
• Galaxy Cluster in Hydra/Centaurus
• Galaxy Clustes in Coma Berenices/Leo
• Zeta Scorpii Region
• Galaxy Cluster Abell 1367
• Centaurus Cluster, Abell 3526
• M45, Pleiades Large Magellanic Cloud (two page spread)
• Virgo/ Coma Galaxy Cluster
• Tarantula Nebula
• M11/ Scutum Star Cloud
• Small Magellanic Cloud
• Virgo Galaxy Cluster

Uranometria 2000.0’s Galaxy Database

Uranometria 2000.0 plots 25,895 galaxies. They are shown as open ovals, with objects larger than 5' drawn to scale. Galaxies with a major axis less than 5' are binned into one of three groups, using symbols to represent the following size ranges: 5'–2', 2'–1', and less than 1'. On the 2× close-up maps, galaxies larger than 2.5' are plotted to scale, and those smaller than 2.5' are binned as follows: 2.5'–1', 1'–0.5', and smaller than 0.5'. On the 3× close-up maps, if larger than 1.7' they are plotted to scale while those that are 1.7' or smaller are binned as follows: 1.7'–0.6', 0.6'–0.3', and less than 0.3'. For all galaxies other than those that have equal major and minor axes, the symbol is oriented on the chart in the direction of the major axis.

Most galaxies have been listed in more than one of the “standard” catalogs. In this work we have adopted the following labeling precedence: New General Catalogue (NGC), Index Catalogue (IC) Uppsala General Catalogue (UGC), European Southern Observatory (ESO), Morphological Catalogue of Galaxies (MCG), Catalogue of Galaxies and Clusters of Galaxies (CGCG), and Catalogue of Principal Galaxies (PGC). Galaxies are complete star systems. A typical one is composed of billions of stars, while the largest can easily exceed a trillion stars. For the most part, clusters and nebulae in other galaxies are well out of visual range. Amateurs equipped with large scopes will be able to observe detail in only a few hundred of the brightest examples.

For this work galaxies were selected that have a B magnitude of 15 or brighter, or a major axis of 1.5 arcminutes or larger. As noted before, all NGC objects are included regardless of magnitude or size. Positions, dimensions, and position angles were confirmed, or modified where necessary, by visual inspection using Digitized Sky Survey images. There are undoubtedly still some identification and positional problems in the resulting galaxy database, but we believe that the procedures we have followed have greatly reduced their number.

Position angles (PA) are given for noticeably elongated galaxies and were obtained directly from a visual inspection of the DSS. Obviously, position angles do not apply to circular objects. These angles, expressed in degrees, are measured from north through east. A value of 0º implies a north-south elongation. A PA of 90º indicates an east-west elongation. After a further quarter-turn counterclockwise, the object is oriented.

Uranometria 2000.0’s Galaxy Cluster Database

This atlas contains 671 galaxy clusters derived from George Abell's 1958 catalog based upon photographs from Mt. Palomar Observatory. In 1980 Abell issued a revision to this catalog, and in 1984 he died while engaged on a southern extension of it using photographs taken at the Anglo-Australian observatory. This work was expanded upon and subsequently completed in 1989 by Harold Corwin and Ronald Olowin. Objects from the 1958 catalog are designated herein with an "A," while those from the 1989 extension bear an "AS" prefix.

Diameters for "A" objects are taken directly from Abell’s revised catalog. Similar data was not available for the "AS" clusters so the diameters were estimated based upon the distance class. For all "A" objects having the same distance class, mean diameters were computed, and those values were applied to the "AS" clusters. Therefore, these dimensions are indicative only, not precisely measured.

Until the advent of very large amateur telescopes and CCD imaging these objects were well beyond the reach of the amateur community.

Uranometria 2000.0's Open Cluster Database

This atlas plots 1,617 open clusters, including those in the Magellanic Clouds. They are shown as dotted open circles, with objects larger than 5' drawn to scale on the main charts.

True open clusters are relatively young objects scattered throughout the disk of the Galaxy. A familiar example is the Pleiades, found on Chart 78. These objects are also known as Galactic clusters, since all but those nearest the Earth are found near the plane of our Galaxy (Chart 8 shows twenty-seven). Over time many objects cataloged as clusters have been proven to be just chance groupings or apparent groupings of unrelated stars. Many of these objects have NGC or IC designations and are well established in the literature. We have chosen to include them as clusters here. The companion DSFG provides specifics.

In the very youngest cases, the remnants of the gas from which they formed are visible as nebulae in the surrounding field. In fact, a small number (78) of open clusters share a single designation with their nebulae. An example is IC 1396 on Chart 19, which is listed as both an open cluster and a bright nebula in the respective sections, has two separate symbols on the chart, and is listed twice in the Index.

The number of stars in these objects ranges from only a few to thousands. In appearance they vary from rich, compact, easily distinguished objects, to a few stars so loosely grouped that they are hardly discernible from the surrounding star field. Many of the latter require experimentation with different apertures and magnifications to be seen. Small telescope users will probably be able to view a larger percentage of open clusters than other types of deep-sky objects.

The principal source used for data on these objects is the book Star Clusters by Brent Archinal and Steven Hynes, in press, to be published by Willmann-Bell. This atlas uses a subset of that data which was selected by a review of the entire catalog by direct inspection of the DSS images by DSFG co-author, Murray Cragin. His criteria were general visibility and the likelihood that the object could be seen by amateurs.

Uranometria 2000.0’s Globular Cluster Database

Some 170 globular clusters, including both Milky Way and Magellanic Cloud objects; are contained in this atlas. They are shown as a continuous- line open circle with an internal cross. On the main charts globulars larger than 5' are drawn to scale; on the 2× close-up maps they are to scale if their diameter is larger than 2.5', and on the 3× maps, if they are larger than 1.7'.

While open clusters have irregular outlines, globulars are strongly circular, and their stars are much more numerous, and densely packed toward the center. They are among the oldest objects to be found in galaxies, with ages near 13 billion years. The number of stars comprising them can range from 10,000 to over 100,000. While open clusters are found strictly in the Galactic plane, globulars are grouped into two regions: around the “hub” at the center of our Milky Way and in its extended Galactic halo. All are gravitationally bound to our Galaxy even though a few are twice as far from its center as the Magellanic Clouds! Globulars are most numerous in the direction of the Galactic center (Chart 146 shows 22 of them), although many of these are greatly dimmed by interstellar dust (the non-NGC globulars listed for Chart 145 are examples).

Uranometria 2000.0's Star Cloud Database

We have chosen to plot 14 star clouds. These objects are composed of countless stars and often span vast stretches of the night sky. When viewed at low power the nebulosity is often overlaid with sparkling stars which often do not show up in photographs. Usually star clouds are so vast that they cannot be plotted on a large-scale atlas however Chart 164 plots 7: NGC 6360, 6415, 6421, 6437, 6455, 6476 and 6480. Another, M24 on Chart 145 is a visually striking star cloud that contains a number of other observable objects. Because there are so few of these plotted objects we have not included them in the legend but have assigned a special symbol and annotated the name with “(star cloud)” to aid in their identification. The symbol sizing is the same as that used for open clusters.

Uranometria 2000.0's Bright Nebulae Database

We draw to scale 377 bright nebulae with a solid outline if larger than 10'. Objects smaller than 10' are drawn as solid-line square boxes in two sizes (10' to 5' and less than 5'). On the 2× close-up maps they are plotted to scale if larger than 2.5'; on the 3× maps, if larger than 1.7'. These objects, also called diffuse or Galactic nebulae, occur in two main classes depending on their source of illumination: emission and reflection, although they occasionally are a combination of the two. Much less common is a third type of bright nebula, the supernova remnant (SNR).

Emission nebulae are clouds of dust and glowing hydrogen gas, sometimes referred to as H II (“H-two”) regions. The atoms in the cloud are ionized by nearby hot stars, and when the excited electrons fall back to their previous energy state, the process releases energy in the form of visible light. A well-known example is the Lagoon Nebula, found on Charts 145 and 146. Since most of the light visible from emission objects comes from just the three lines produced by hydrogen (Hß at 4861Å) and oxygen ([OIII] at 5007Å and 4959Å), the use of narrow band "nebula" filters can be helpful in viewing them.

Reflection nebulae have the same composition as emission objects but lack stars sufficiently hot to cause the gas comprising them to fluoresce; therefore, they shine merely by the dust in the nebulae scattering starlight (the gas does not actually reflect any light). Good examples are the nebulosities surrounding the Pleiades star cluster (Chart 78) and M78 in Orion (Chart 116). Because these objects scatter starlight of all colors, filters are not generally helpful in viewing them.

A supernova remnant is the remains of a catastrophic stellar explosion, wherein much of a star’s material is ejected, often as a highly-structured cloud. Examples are the Veil Nebula in Cygnus (Chart 47) and the Crab Nebula (M1) in Taurus (Chart 77). These objects have strong emission lines similar to H II regions, hence also benefit from the application of nebula filters.

Uranometria 2000.0’s Dark Nebulae Database

This atlas contains 367 dark nebulae, which are drawn to scale with a dashed outline if larger than 10'. Objects smaller than 10' are drawn as dashed-line square boxes in two sizes (10' to 5' and less than 5'). On the 2× close-up maps they are plotted to scale if larger than 2.5', on the 3× maps, if larger than 1.7'.

Dark nebulae are composed of clouds of dust and gas sufficiently dense as to become opaque. They are detectable if positioned between the observer and a bright nebula or a very dense star field, against which they can be seen silhouetted. Observationally, dark nebulae are among the most difficult deep-sky objects. The Coalsack, near the Southern Cross (Charts 198 and 209), is an example clearly visible to the unaided eye because it happens to lie in front of the rich, starry background of the Milky Way. On the other hand, the well-known Horsehead Nebula (cataloged as Barnard 33 on Chart 116) is much more typical. It is a difficult object because of its small size and because it lies in front of a rather faint background object, emission nebula IC 434. In this case the resulting contrast between the dark nebula and background is very low, making it difficult to distinguish. Dark nebulae are usually seen best with wide-field, low-power eyepieces, which provide a large, bright surrounding field. While these objects emit no light of their own, nebula filters may help increase the contrast if the background is an emission nebula.

Uranometria 2000.0's Planetary Nebulae Database

1,144 planetary nebulae are plotted, shown as open circles with four protruding lines, in four sizes representing the following categories: those having diameters greater than 30?, 30? to 10?, 10? to 5? and less than 5?. On the close-up charts two additional symbols are used: greater than 60? and 60? to 30?.

Planetary nebulae are shells of gas thrown off by stars having approximately the Sun’s mass, that are nearing the end of their evolutionary cycle following the red-giant stage. The shell gradually expands, until after perhaps 100,000 years it becomes undetectably thin and all that remains is the central star. Some of the earliest such objects discovered (e.g., NGC 3242 on Chart 151, and NGC 6210 on Chart 68) were found by William Herschel, who noted the resemblance of their well-defined disks to those of planets, and gave them the name “planetary nebulae”, but of course they have nothing to do with planets.

The brightest planetaries have a substantial disk, typically 30 arcseconds across, but the majority listed here are stellar (or nearly so) and can be identified at the eyepiece only with a nebula filter or direct-vision prism. Chart 164 lists over 100 such objects, hardly any of which are larger than a few arcseconds in diameter. A few of the oldest and nearest examples are so distended as to be practically invisible against the background sky. Between these two extremes are planetaries that come in about as many shapes as there are objects, including the aptly-named Ring Nebula on Chart 49 and the complex southern object NGC 5189 on Chart 208.

Invisible light, planetary nebulae shine predominantly at the two wavelengths emitted by doubly-ionized oxygen, denoted by the symbol [OIII]. Typically, 90% of the visually-detectable light comes from the [OIII] lines at 5007Å and 4959Å in the blue-green part of the spectrum. As a result, when an [OIII] filter is placed between the eye and the eyepiece, stars are dimmed by as much as three magnitudes (the night-sky light even more), while light from a planetary passes through virtually unchanged. By rapidly passing an [OIII] filter between the eye and eyepiece and out again while examining the field, a planetary will usually appear to “blink” as the stars are dimmed, and the nebula maintains its brightness. There are a few planetaries that have weak [OIII] emission (a bright example is PN G64.7+5.0, Campbell’s Hydrogen Star, on Chart 48), and these are best viewed either directly or with an Hß filter, which passes the line that is brightest in these cases.

Uranometria 2000.0's Radio Source Database

Radio Sources - These objects are shown as open triangles when the source is invisible or below the chart’s limit. There are about 260 of them plotted in this atlas. About 100 additional sources are both radio and quasi-stellar objects or x-ray emitters. Where the visible source is plotted, as in the case of a bright star (e.g. d Cas) or a galaxy, the special symbol does not appear. In order of preference they are identified by their designation from the Third Cambridge Catalogue of Radio Sources (3C), the 4C number and then PKS without prefix formed by concatenating the hours and minutes of R.A. with declination truncated to tenths of a degree.

Uranometria 2000.0's X-Ray Source Database

These are shown with an open centered "X" in cases where the source is invisible or below the chart's limit. About 35 of them are included herein. Where the visible source is plotted, the special symbol does not appear. Objects are generally labeled by common name (e.g. M82, NGC 1815, LMC S-2 [Large Magellanic Cloud], or ? Cas).