The Sharpless Catalog

Click on the small images to see larger ones.

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Sh 2-21

Coordinates: (0.59°, -0.86°)
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This HII region is located in the galactic bar below the galactic plane and is associated with the infrared star clusters [DB2000] 7, [DB2000] 10, [DB2000] 11 and [DB2000] 12.

Sh 2-22

Coordinates: (4.28°, 0.55°)
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This is a ring nebula surrounding the O8 III giant 63 Ophiuchi (HD 162978), which lies at the edge of the Sgr OB1 association in the Sagittarius arm.

You can see the full extent of this huge object in this SuperCOSMOS image.

Sh 2-23

Coordinates: (4.32°, 29.6°)
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There is nothing significant on this nebula in the scientific literature. It is close to the A4V star 16 Scorpii and may possibly be a faint reflection nebula.

Dean Salman has a good image of this object on his Sharpless nebula website.

Both Sh 2-23 and Sh 2-24 can be seen together in this IRAS infrared image. Sh 2-24 is the bright ellipse and Sh 2-23 is the much fainter squiggle below and to the right.

Sh 2-24

Coordinates: (5.1°, 30.85°)
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The eerie blue glow of MBM 57 is at a distance stretching between 50 and 240 pc, making it one of the closest known molecular clouds.

Dean Salman has a good image of this object on his Sharpless nebula website.

Both Sh 2-23 and Sh 2-24 can be seen together in this IRAS infrared image. Sh 2-24 is the bright ellipse and Sh 2-23 is the much fainter squiggle below and to the right.

Sh 2-25

Coordinates: (6.09°, -1.29°)
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The Lagoon nebula (M8 = NGC 6523-NGC 6530) is
a large HII region mainly ionized by two O-class stars, the ultrahot O4V class 9 Sagittarii and the binary HD 165052 (O6.5V + O7.5V). Sharpless also lists 12 B-stars that may also ionise the nebula. It also includes the radio source W 29.

The Lagoon nebula is a major feature of the Sgr OB1 association in the Sagittarius arm. It is embedded within a molecular cloud which extends to the star cluster NGC 6530. The Hourglass nebula lies within M8’s core. This is a blister-type HII region which has been produced by the O7.5V star Herschel 36.

There is a good image of the the Lagoon nebula here and an amazing wide angle image of the whole region that includes the entire RCW 146 complex and the Trifid nebula.

Sh 2-26

Coordinates: (6.19°, 0.35°)
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This diffuse nebula is part of the large region of nebulosity near the Trifid nebula that includes RCW 145.

No ionising stars for Sh 2-26 are listed in the scientific literature but the nebula clearly surrounds the O9 III giant LS 4511 so this may be the ionising star.

Sh 2-27

Coordinates: (6.28°, 23.59°)
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This is an extended HII region around the nearby O9 V star Zeta Ophiuchi. The spectacular bow shock caused by this star as it ploughs through dense dust clouds near the Sco OB2 association can be seen in this infra-red image from the Milky Way Explorer.

Sh 2-28

Coordinates: (6.6°, 0.1°)
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This large faint HII region next to the Trifid nebula is ionised by the O9Ib supergiant LS 4551 and the O-class LS 4538, It lies in the direction of the supernova remnant SNR G006.4-00.1 (W 28).

You can view a SuperCOSMOS hydrogen-alpha image.

Sh 2-29

Coordinates: (7.0°, -2.16°)
[ See details ]

Sh 2-29, Sh 2-31, and Sh 2-32 are a group of three nebulae next to the much larger Lagoon nebula. Sh 2-29 is the largest of the three. This group is combined together in the RCW (RCW 146c) and Gum (Gum 75) catalogs.

Avedisova concludes that Sh 2-29 is ionised by the O9 IV subgiant HD 165921.

Sh 2-30

Coordinates: (7.0°, -0.2°)
[ See details ]

The Trifid nebula, M 20, is an HII region ionised by the O7.5 class multiple star HD 164492 (with seven known components), which is a member of the star cluster NGC 6514. It is divided into three parts by dust lanes. A blue reflection nebula surrounds the HII region.

The Trifid nebula is usually assumed to be part of the Sgr OB1 association in the Sagittarius arm, along with the Lagoon nebula. However, the surprisingly large range of distance estimates for the nebula leaves open the possibility that it lies much further away in the Centaurus arm.

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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.