The Sharpless Catalog

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Sh 2-41

Coordinates: (12.72°, -0.68°)
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Sh 2-41 is a large diffuse nebula and a major component of Messier 24, the Small Sagittarius Star Cloud. Although Messier 24 is not a real object (being made up of many objects at different distances), Sh 2-41 is a real HII region surrounding the Sgr OB4 association, which includes the multiple O7 III giant HD 167771. You can see an image of the entire Messier 24 region here.

Sh 2-42

Coordinates: (13.34°, 1.16°)
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Sh 2-42 is believed to be the planetary nebula PN G013.3+01.1.

Sh 2-43

Coordinates: (13.52°, -0.4°)
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This faint diffuse nebula is close in direction to the suspected supernova remnant GAL 013.1-00.5 and appears to be located in an empty region bordered by the OB regions Sgr OB1, Sgr OB7 and Sct OB3.

Avedisova places Sh 2-43 / RCW 156 into star formation region SFR 13.62-0.76 along with two infrared sources and many molecular clouds.

No ionising star for Sh 2-43 has been identified in the scientific literature and no ionising star in this direction appears in the Reed catalog or SIMBAD either. The bright star in this image is the K2 III giant HD 167720.

Sh 2-44

Coordinates: (14.2°, -0.1°)
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This huge almost circular nebula is very prominent in hydrogen-alpha as can be seen in this SuperCOSMOS image.

Avedisova concludes that it is ionised by the O6 V star HD 167633. Humphreys places this star in the Ser OB1 association in the Sagittarius arm.

However, several other sources give larger distance estimates, placing this nebula in the Centaurus arm, where it may be part of the Scutum supershell.

Sh 2-45

Coordinates: (15.1°, -0.7°)
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This is M 17, the Omega nebula, also called W 38, the Swan nebula, and the Lobster nebula among other names. This nebula is found in the Ser OB1 association.

M 17 is ionised by an O4V-O4V double star system (Kleinmann's star) at the core of the massive young cluster NGC 6618 (about one million years old), which contains over 800 stars, including 2 O5V star systems and 100 stars hotter than B9 (by comparison, the Orion nebula contains 8 stars hotter than B9). The total ultraviolet flux is about 25 times higher than for the Orion nebula.

A large part of the nebula is hidden by a dark dust lane that runs near the central cluster and splits the main visible nebula (Gum 81a) from two attached nebulae on the other side of the dust lane (Gum 81b - IC 4706 and IC 4707).

M 17 is a blister on the side of a much larger giant molecular cloud and star formation region (M 17SW) that contains 30 thousand solar masses of molecular hydrogen.

You can see a more detailed image of part of this massive star formation region and view a good overview of this entire region.

Sh 2-46

Coordinates: (15.18°, 3.33°)
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This isolated nebula is located well above the galactic plane.

Avedisova concludes that it is ionised by the potential runaway O9.5 Iab supergiant HD 165319, which may have been ejected from NGC 6611, the central star cluster of M 16, the Eagle nebula, about 1.8 million years ago.

Sh 2-47

Coordinates: (15.24°, 0.16°)
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According to Avedisova, the ionising star for this small nebula is probably the B0.5 III giant star [L85] S47 3.

Sh 2-48

Coordinates: (16.6°, -0.3°)
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This nebula may be associated with the Scutum supershell in the Centaurus arm.

Avedisova places it in star formation region SFR 16.65-0.34 along with the molecular clouds SYCSW 164, SYCSW 164A and SRBY 52. She concludes that Sh 2-48 is ionised by the O8 V multiple star ADS 11285.

The newly discovered dense star cluster Kronberger 25 appears in the same direction as Sh 2-48, although a tentative distance estimate for this cluster of about 2000 parsecs suggests that it may be a foreground object.

Sh 2-49

Coordinates: (16.8°, 0.75°)
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This is M 16, the Eagle Nebula. It is part of the W 37 molecular cloud and is ionized by the NGC 6611 star cluster, which is part of the Ser OB1 association in the Sagittarius arm. NGC 6611 is dominated by the massive and superhot O3.5V+O7.5V class multiple star HD 168076, which has 75-80 solar masses and provides about half the ionising radiation for the nebula.

There is a much better image of the Eagle nebula here. A region of M 16 was the subject of perhaps the most famous Hubble space telescope image, the 1995 Pillars of Creation.

Sh 2-50

Coordinates: (16.93°, -1.07°)
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Sh 2-50 appears in the direction of the Sct OB3 association and the star cluster Dolidze 28, which has the Wolf-Rayet star WR 115 as its central star.

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Stewart Sharpless published the second and final version of his famous nebula catalog in 1959. Although astronomers publish articles referring to the Sharpless nebulae almost every month, there seems to be few places on the Internet that bring together information on these nebulae as a whole - unlike, for example, the Messier catalog. This is most likely because the Messier objects are visible to anyone with a pair of binoculars or a small telescope. Most of the Sharpless objects are clearly visible only in CCD images or in photographic plates taken by large telescopes. Fortunately some of these plates have now been digitally scanned and made publicly available.

Many of the brightest and most beautiful Milky Way star formation regions visible from the northern hemisphere are in the Sharpless catalog so the 313 objects it contains are well worth examining carefully. (In fact there are more than 313 objects as subsequent research has shown that some of the Sharpless nebulae consist of more than one object.) Although the Sharpless catalog is only intended to be complete for objects visible north of declination -27 degrees, a similar catalog covering the southern hemisphere was published by Alex Rodgers, Colin Campbell, and John Whiteoak in 1960, which is largely an expansion of Colin Gum's earlier catalog. You can visit a gallery of these RCW nebulae here. At least 50 objects in the Sharpless catalog are also in the RCW catalog and I have noted this in the descriptions of these objects.

Most of the images used to illustrate the Sharpless catalog were created using the POSS-II/UKSTU data of the Digitized Sky Survey, or, where available, the more detailed SuperCOSMOS Sky Survey. In both cases, green = UKST Infrared. Because green represents infrared, the images are not quite the same as would be seen at purely visual frequencies. Green in these images usually reveals warm dust or red giant stars.

These images were created using the POSS-II/UKSTU data of the Digitized Sky Survey and SuperCOSMOS using the process described here.

According to my correspondence with the Royal Observatory Edinburgh and the Space Telescope Science Institute, I am allowed to use the POSS-II/UKSTU data to create and display images for non-commercial purposes so long as I include this fine print for the SuperCOSMOS data:

Use of these images is courtesy of the UK Schmidt Telescope (copyright in which is owned by the Particle Physics and Astronomy Research Council of the UK and the Anglo-Australian Telescope Board) and the Southern Sky Survey as created by the SuperCOSMOS measuring machine and are reproduced here with permission from the Royal Observatory Edinburgh.

and this acknowledgement taken from the DSS site:

The Digitized Sky Surveys were produced at the Space Telescope Science Institute under U.S. Government grant NAG W-2166. The images of these surveys are based on photographic data obtained using the Oschin Schmidt Telescope on Palomar Mountain and the UK Schmidt Telescope. The plates were processed into the present compressed digital form with the permission of these institutions.

The Second Palomar Observatory Sky Survey (POSS-II) was made by the California Institute of Technology with funds from the National Science Foundation, the National Geographic Society, the Sloan Foundation, the Samuel Oschin Foundation, and the Eastman Kodak Corporation.

The UK Schmidt Telescope was operated by the Royal Observatory Edinburgh, with funding from the UK Science and Engineering Research Council (later the UK Particle Physics and Astronomy Research Council), until 1988 June, and thereafter by the Anglo-Australian Observatory. The blue plates of the southern Sky Atlas and its Equatorial Extension (together known as the SERC-J), as well as the Equatorial Red (ER), and the Second Epoch [red] Survey (SES) were all taken with the UK Schmidt.

The "Second Epoch Survey" of the southern sky was made by the Anglo-Australian Observatory (AAO) with the UK Schmidt Telescope. Plates from this survey have been digitized and compressed by the ST ScI. The digitized images are copyright © 1993-5 by the Anglo-Australian Observatory Board, and are distributed herein by agreement.

The "Equatorial Red Atlas" of the southern sky was made with the UK Schmidt Telescope. Plates from this survey have been digitized and compressed by the ST ScI. The digitized images are copyright © 1992-5, jointly by the UK SERC/PPARC (Particle Physics and Astronomy Research Council, formerly Science and Engineering Research Council) and the Anglo-Australian Telescope Board, and are distributed herein by agreement.

The compressed files of the "Palomar Observatory - Space Telescope Science Institute Digital Sky Survey" of the northern sky, based on scans of the Second Palomar Sky Survey are copyright © 1993-1995 by the California Institute of Technology and are distributed herein by agreement. The compressed files of the "Palomar Observatory - Space Telescope Science Institute Digital Sky Survey" of the northern sky, based on scans of the Second Palomar Sky Survey are copyright © 1993-1995 by the California Institute of Technology and are distributed herein by agreement.