Per Dreyer, NGC 6500 is "very faint, very small, southwestern of 2", the other being NGC 6501. Based on a recessional velocity of 3005 km/sec, NGC 6500 is about 140 million light years away. Given that and its apparent size of 2.2 by 1.6 arcmin, it is about 90 thousand light years across. Since they are in nearly the same direction and at nearly identical distances, NGC 6500 and 6501 are almost certainly a physical pair.

Per Dreyer, NGC 6500 is "very faint, very small, northeastern of 2", the other being NGC 6500. Based on a recessional velocity of 3070 km/sec, NGC 6501 is about 145 million light years away. Given that and its apparent size of 2.0 by 1.8 arcmin, it is about 85 thousand light years across. Since they are in nearly the same direction and at nearly identical distances, NGC 6500 and 6501 are almost certainly a physical pair.

Apparent size 1.3 by 1.1 arcmin

The second IC adds "is bright or pretty bright". Apparent size 7.0 by 2.5 arcmin. Approximately 30 thousand light years across and 17 million light years away, the dwarf spiral lies in solitary splendor just inside the Local Void, a nearly empty region of space several tens of millions of light years across bounded by our Local Group, the Hercules Cluster and the Coma Cluster.

Apparent size 2.2 by 0.5 arcmin

Apparent size 1.1 by 1.0 arcmin

Apparent size 7.0 arcmin

Apparent size 1.3 by 1.3 arcmin

Apparent size 1.6 by 1.2 arcmin

Per Dreyer, NGC 6510 is "most extremely faint, pretty small, a little extended, very difficult." (this entry to contain only historical information; for physical data and images see NGC 6511)

Per Dreyer, NGC 6511 is "faint, pretty large, brighter middle, (? = last one)", the last comment indicating that Dreyer thought it might be the same as NGC 6510, which turned out to be the case. However, the second IC listed a corrected RA (per Bigourdan) of 17 53 06, and added "6510 is 44 seconds to the west", so the suspected identity of the two listings was (incorrectly) abandoned. Apparent size 1.0 by 0.6 arcmin.

Apparent size 0.5 by 0.4 arcmin

Apparent size 1.2 by 0.9 arcmin

The name of the nebula refers to the way that dust lanes lying in front of it seem to divide it into three lobes. It consists of emission and reflection nebulae energized and lit up by hot, bright young stars recently formed from the gas and dust in the nebula, and actively heating and eating away at the remaining gas. The Trifid Nebula is probably around 6000 light years away, but distance estimates range from 3000 to 9000 light years, so the actual distance is very uncertain. If at 6000 light years distance, the 20 arcmin apparent size of the nebula would correspond to about 100 light years.

Apparent size 1.6 by 1.0 arcmin

Apparent size 0.5 by 0.2 arcmin

Apparent size 4.0 arcmin

Apparent size 0.4 by 0.4 arcmin

Apparent size 5.0 arcmin

Based on a recessional velocity of 8235 km/sec, NGC 6521 is about 380 million light years away. Given that and its apparent size of 1.6 by 1.3 arcmin, it is about 180 thousand light years across. It is a Seyfert galaxy (type Sy1.9).

Based on a recessional velocity of 7685 km/sec, PGC 61141 is about 360 million light years away. Given that and its apparent size of 0.8 by 0.25 arcmin, it is about 85 thousand light years across. The difference in the radial velocities of PGC 61141 and NGC 6521 suggests that they are merely an optical double. Even in the unlikely event that they are at the same distance and their different radial velocities represent a peculiar (non-Hubble expansion) relative velocity, the magnitude of the difference means they cannot be gravitationally bound.

Per Dreyer, NGC 6523 (= Lacaille III 13, Messier 8, 1860 RA 17 55 06, NPD 114 22.8) is "a magnificent object (!!!), very bright, extremely large, extremely irregular figure, with large cluster". (Dreyer's ignoring Le Gentil's observation in favor of Lacaille's of 1751 is the least of many unkind fates visited upon Le Gentil during and after his eleven year expedition to observe the transits of Venus.) The position precesses to RA 18 03 41.1, Dec -24 22 56, dead center on the brightest part of the Lagoon Nebula, so the identification is certain. The only question is how the numerical listings should be used. It should be kept in mind that in Dreyer's day, "The Lagoon Nebula" only referred to the brighter regions visible with the eye (admittedly, with the aid of a telescope). The much larger luminous structure visible with modern photographic technology, which has usurped the title, was not part of the original Lagoon; so although the Lagoon is often referred to as NGC 6523 or M8, neither of those terms included the fainter regions which make up the modern Lagoon. Instead, several NGC/IC listings refer to various parts of what is now referred to as "M8", "NGC 6523", or "The Lagoon Nebula":
     The brightest part of the nebula, to the northwest of its historical center, is NGC 6523. The fainter region to the southeast is NGC 6526. The combination of those two regions is William Herschel's NGC 6533, and in Dreyer's day would have been considered the entire Lagoon Nebula. In fact the open cluster NGC 6530 was listed as being to the east of M8, despite being more nearly in the center of the "modern" Lagoon. (The labeled image below shows the three distinct structures, but does not indicate the identity of NGC 6533, which see for further discussion. Additional "objects" located still further to the east, IC 1271 and 4678, are not labeled in the current version of the image but will be added when the entries for the Lagoon are finalized.)

Below, a HST closeup of the region near the "Hourglass" (shown in the upper left corner of the image), the brightest part of the Lagoon Nebula. The reddish star near the Hourglass is actually a very hot bluish-white star seen through clouds of obscuring dust. The star is heating up the surrounding gas, evaporating and blowing it away, and apparently contorting it into "twisters" (at the far upper left); but whether the gas in the twisters is actually spiraling as in an earthly tornado or is simply evaporating in what appears to be a twisted shape remains to be determined by a future generation of telescopes. (Image Credits: A. Caulet (ST-ECF, ESA) and NASA)

Apparent size 1.4 by 1.0 arcmin

Apparent size 4.0 arcmin

Per Dreyer, NGC 6526 (= John Herschel's GC 4363, 1860 RA 17 55 40, NPD 113 27.5) is "faint, large, extremely extended". The second IC added (per Howe) "Only very faint stars". The position precesses to RA 18 04 11.5, Dec -23 27 31, a degree north of the proper place; but (per Corwin) although not mentioned in the NGC, Dreyer (later) wrote a separate paper about Herschel's observations, in which he noted a one degree error in Caroline Herschel's reduction of her brother's data for this object, so the identification is certain (presuming an error of exactly one degree, a corrected precessed position would be RA 18 04 15.4, Dec -24 27 31, well within the region considered to be NGC 6526). As noted at NGC 6523, there are several NGC/IC listings for the "modern" Lagoon Nebula. NGC 6526 is the moderately bright region between NGC 6523, the brightest part of the nebula, and NGC 6530, an open cluster recently formed from the gas and dust surrounding it. The labeled image below shows their relative positions.

Below, a cropped Misti Mountain image of M8 shows NGC 6526 at bottom right, NGC 6530 at top left, and the "Southern Cliff" stretching across the bottom of the cutout (Image Credits and © Jim Misti, Misti Mountain Observatory; used by permission)

Apparent size 1.4 by 1.0 arcmin

Apparent size 5.0 arcmin. Located within Baade's Window, a region of the Milky Way relatively unobscured by dust.

(See Giovanni Hodierna for a discussion of why none of his discoveries were credited in the NGC/IC catalogs.) Per Dreyer, NGC 6530 (= John Herschel's GC 4366, 1860 RA 17 56 06, NPD 114 20.0) is a "cluster, bright, large, pretty rich, to the east of M8", meaning to the east of the brighter regions of the Lagoon Nebula, listed as NGC 6523 and 6526. The position precesses to RA 18 04 40.9, Dec -24 19 55, which is well within the bounds of the cluster; but even if it were not, the description of the location makes the identification certain. The cluster has an apparent size of 15 arcmin. As noted at NGC 6523, there are several NGC/IC listings for the "modern" Lagoon Nebula. NGC 6523 and NGC 6526 comprise the historical definition of the Lagoon, while NGC 6530 lies to their east, as noted by Dreyer. The labeled image below shows their relative positions.

Above, a labeled image of the Lagoon Nebula, showing NGC 6523 (which see for credits), 6526, and 6530. Note that although NGC 6530 is to the east of the "original" Lagoon, the much larger luminous region which is now called the Lagoon Nebula fills most of this image, and extends well to the east of the cluster and well to the west of the brighter regions which used to hold that title. Below, an image of the historical Lagoon and NGC 6530 (Image Credits and © Jim Misti, Misti Mountain Observatory; used by permission)

M21 is a tightly compacted cluster of about 60 stars, scattered across a region 16 arcmin wide. Most of the stars in the cluster are relatively faint, but there is a central concentration of B-type giants. The true brightness of these giants is uncertain, and as a result the distance of the cluster is uncertain, with estimates ranging from just over 2000 light-years to more than 4000 light-years. The lifetimes of such blue giants are only about 1/1000th of the age of the Solar System, so the cluster must have been formed no more than 4 to 5 million years ago.

The second IC lists a corrected RA (per Bigourdan) of 17 56 43. Apparent size 1.8 by 0.9 arcmin.

Per Dreyer, NGC 6533 (= John Herschel's GC 4368 = V 13, 1860 RA 17 56 32, NPD 114 53.4) is "extremely large, extremely irregular figure, star following". (Note: V 13 is in Dreyer's column for "other observers", and as a result is listed as such in some references, such as the NGC/IC Project. However, it is a printing error, and actually refers to William Herschel's list V#13.) Why Dreyer did not give credit to the earlier observations by Le Gentil and Messier (as he did for NGC 6523) is unknown; but as noted in other places, the NGC was an updating of the GC, and in many cases only lists John and William Herschel's observations. Aside from that, NGC 6533 refers to the combined region also cataloged as NGC 6523 and 6526, so Dreyer may have been noting that Herschel was the first to assign a position to the overall structure. The position listed in the NGC precesses to RA 18 05 09.1, Dec -24 53 14, which is half a degree south of the correct position; but a detailed drawing of the region by John Herschel and the description provided in Dreyer's catalog make the identification certain (per Corwin, the error can be reduced to zero by assuming that Herschel misidentified the comparison star as 5 Sgr instead of 4 Sgr). The only question is, as noted for the other NGC listings corresponding to the Lagoon Nebula, which numbers apply to which regions. As shown in the labeled drawing below (and at the individual listings), NGC 6523 applies to the brightest part of the Lagoon, which is the western portion of Herschel's nebula. NGC 6526 applies to the fainter region to its east, which is the eastern portion of Herschel's nebula. NGC 6350 is the cluster of stars to their east, which with visual observations appears to be to the east of the Lagoon; but in the photographic images shown below, the Lagoon is a much larger structure than anything visible with the eye, and as a result, the cluster is more nearly in the center of the "modern" Lagoon. Two IC listings also apply to fainter regions off to the east, as shown in the very wide field image at the end of this entry.
     The Lagoon Nebula lies about 5000 light-years from the Earth, in the direction of the constellation of Sagittarius (and hence, toward the center of our galaxy). It is best seen telescopically at very low power, as its 100 light-year span is nearly three times the half-degree diameter of the Moon (although the part referred to as NGC 6533 is only about 45 by 30 arcmin, or half again the size of the Moon). Its visual appearance is of a ghostly gray cloud spread across the starry background formed by stars lying between us and it, and within its star-forming regions. As shown by the varying appearance of the images below, its photographic appearance depends upon the artistic whims of the the person who chooses the colors representing different wavelengths inside or outside the visible spectrum.

Below, a comparison of part of the visible-light image above to an infrared view of the same region, showing the stars hidden within and behind the Lagoon, and clouds of dark dusty material which are normally lost in the glow of the emission nebula (Image Credits: ESO/VVV, Acknowledgment: Cambridge Astronomical Survey Unit)

The second IC added "is large, 1 or 2 arcmin diameter, not very small". Apparent size 3.4 arcmin.

Apparent size 1.2 by 1.1 arcmin

Apparent size 0.17 arcmin

Apparent size 1.0 by 0.5 arcmin

Apparent size 7.9 arcmin

This object looks like a small group of just a few slightly brighter stars surrounded by the multitudinous background of Milky Way stars in any reasonable size telescope, and was therefore misclassified as an open cluster until the late 1900's. However, it is actually a globular cluster. A color-magnitude diagram indicates that the cluster is about 11 thousand light years from the Sun, and its direction places it almost exactly halfway between the Sun and the center of our Galaxy. Given that and its apparent size of 1.5 by 1.0 arcmin, the cluster is about 5 light years across, which is very small in comparison to most globulars. Its irregular shape is also unusual, and has been suggested as being due to the merger of two smaller clusters.

Apparent size 15 arcmin

Apparent size 1.3 by 0.4 arcmin

The Cat's Eye nebula has long been recognized as one of the most complex planetary nebulae known. Aside from the spectacular lobes and arcs near its center, it is surrounded by a series of concentric spherical shells (ring-like structures, as seen from our point of view) which indicate fairly regular ejections of mass into space. Based on the size and rate of expansion of the shells, it is estimated that they were ejected at 1500 year intervals, with about 1% of a solar mass (or a mass equal to that of all the planets in our Solar System) thrown into space with each ejection. Still further out, but not visible in closeups of the nebula, is a 3 light year wide "outer halo" of chaotically dispersed gas which testifies to a still earlier stage of mass loss. The Cat's Eye was the first planetary nebula in which the central star was observed, and the first to reveal its nature as a cloud of rarefied gas; and its multilayered structure still makes it an object of intense interest and continued study. (Per Steinicke, the main structure is about 0.33 arcmin across.)

Above, an HST image in visible light reveals the complex structure of the nebula. (Image Credits: J. P. Harrington (U. Maryland) & K. J. Borkowski (NCSU) HST, NASA). Below, a Chandra X-ray image (in blue) is superimposed on the visible structure. (Image Credits: X-ray: UIUC/Y.Chu et al., Optical: HST, NASA)

Apparent size 9.2 arcmin

Apparent size 1.1 by 0.9 arcmin

Apparent size 15 arcmin

Apparent size 1.3 by 0.4 arcmin

The second IC states (erroneously) "6548 = 6550, Swift in Cat. XI.". An optical double with NGC 6549 (which is over three times further away), and historically often confused with NGC 6550 due to more than a century of mistaken identity (for a discussion of that, see NGC 6550). Because of the confusion between the various identifications, which data applies to which galaxy is hard to determine. (For instance, the HyperLeda database lists the recessional velocity of NGC 6548 as 2190 km/sec, while the NASA/IPAC NED database lists a recessional velocity of 2210 km/sec, but lists the galaxy as NGC 6550, although the image and position are those shown in the data above and the images below for NGC 6548.) In any event, based on a presumably accurate recessional velocity of 2200 km/sec, the Hubble expansion distance is about 100 million light years, in which case the apparent size of 3.0 by 2.8 arcmins would correspond to a diameter of 90 thousand light years.

An optical double with NGC 6548 (which is over three times closer), and identical to NGC 6550, which see for a discussion of the more than a century of mistaken identity involving the NGC listings for NGC 6548, 6549 and 6550. HyperLeda lists the recessional velocity of NGC 6549 as 6670 km/sec, while NED lists a recessional velocity of 6705 km/sec, but incorrectly identifies the galaxy as NGC 6548, despite using an image and position identical to those shown here for NGC 6549. Using an intermediate recessional velocity of 6690 km/sec, the Hubble expansion distance is about 310 million light years, in which case the apparent size of 1.4 by 0.4 arcmins would correspond to a diameter of 125 thousand light years.