2.1 by 1.1 arcmin

2.0 by 1.5 arcmin

1.3 by 0.6 arcmin

1.1 by 0.2 arcmin

(0.47 arcmin wide?)

(6.7 arcmin wide?)

2.0 by 1.3 arcmin

1.5 by 1.3 arcmin

(3 arcmin wide?)

(0.63 arcmin wide?) (Steinicke notes not a planetary nebula)

(5 arcmin wide?)

1.3 by 0.8 arcmin

3.0 by 2.0 arcmin

1.3 by 0.6 arcmin

1.2 by 0.3 arcmin

1.2 by 0.5 arcmin

2.1 by 0.7 arcmin

1.4 by 0.3 arcmin

1.6 by 0.3 arcmin

1.6 by 1.3 arcmin

Over 100 light years across, and 60 to 100 thousand light years away (6.8 arcmin wide?)

0.8 by 0.6 arcmin

(7 arcmin wide?)

2.0 by 0.7 arcmin

3.6 by 2.8 arcmin

1.6 by 1.3 arcmin

2.6 by 1.3 arcmin

(30 arcmin wide?)

6.0 by 1.5 arcmin

(14 arcmin wide?)

(7 arcmin wide?)

The second IC adds "7th magnitude star 3 arcmin to southwest, not northeast (DeLisle Stewart). h. in Cape Obs. has southeast". 2.4 by 1.4 arcmin

2.7 by 0.4 arcmin

2.7 by 2.4 arcmin (? does not agree with Steinicke type ?)

Listed here because sometimes called NGC 6876A; but more appropriately called IC 4945, which see

1.1 by 0.6 arcmin (? does not agree with Steinicke type ?)

1.6 by 1.3 arcmin

1.8 by 0.8 arcmin

Per Dreyer, NGC 6879 (= Pickering (HN 55), Copeland, 1860 RA 20 04 04, NPD 73 29.3) is a "planetary, stellar, equivalent to 10th-magnitude star". The position precesses to RA 20 10 26.6, Dec +16 55 22, dead center on the star in question, so the identification is certain. As in the case of Pickering's other "stellar" planetaries, NGC 6879 is only a few arcsec across, and appears almost perfectly stellar even under high magnification; however, using a filter (such as an OIII filter) which blocks out all radiation save that emitted by clouds of interstellar gas, it is possible to "blink" the object. Switching the filter in and out causes stars, which emit only a small portion of their light at the wavelengths passed by the filter, look markedly fainter when the filter is in place, while nebulae look nearly as bright with the filter as without.

2.0 by 0.9 arcmin

Per Dreyer, NGC 6881 (= Pickering (HN 44), 1860 RA 20 05 43, NPD 53 00) is a "planetary, stellar". The position precesses to RA 20 10 52.9, Dec +37 24 50, within 0.1 arcmin of the star in question, so the identification is certain. As in the case of Pickering's other "stellar" planetaries (such as NGC 6879), NGC 6881 is only a few arcsec across, and appears almost perfectly stellar even under high magnification; however, using a filter (such as an OIII filter) which blocks out all radiation save that emitted by clouds of interstellar gas, it is possible to "blink" the object. Switching the filter in and out causes stars, which emit only a small portion of their light at the wavelengths passed by the filter, look markedly fainter when the filter is in place, while nebulae look nearly as bright with the filter as without.

(see NGC 6885 for physical data)

(35 arcmin wide?)

Per Dreyer, NGC 6884 (= Copeland, 1860 RA 20 05 59, NPD 43 57.2) is a "planetary nebula, stellar". The position precesses to RA 20 10 23.6, Dec +46 27 37, dead on the star in question, so the identification is certain. (For a discussion of the double listing, and of Pickering's ingenious way of detecting "stellar" planetaries, see NGC 6766.) As for many of the "stellar" planetaries discovered by Pickering and Copeland, NGC 6884 is hardly discernible from an ordinary star save with the use of filters. A "blink" comparison, in which a filter which blocks out light not given off by clouds of interstellar gas, is the easiest way for an amateur observer to tell which of the numerous stars in the region is the planetary nebula. When using such a filter (an OIII filter is the one most commonly used) stars appear noticeably fainter, while nebulous objects are nearly as bright as without the filter; so switching back and forth, the observer looks for objects which "blink" brighter than their neighbors when using the filter. However, as shown in the images below, NGC 6884 does exhibit a nebular ring around the central star. The ring is so much fainter than the star that it would not be visible either visually, or in photographs taken with most amateur telescopes. The "normal" planetary nebula (such as imaged by the HST in the last image below) is part of the stellar object at the center of the ring, and I have yet to find any reference to the ring in the literature. This does not mean that it does not exist, and is merely an "artifact"; it is probably a roughly spherical cloud of material ejected by the central star a few thousand years ago, now faded to insignificance. If so, it represents the eventual fate of all planetary nebulae -- to become so large, so rarefied, and so poorly illuminated that they fade and disappear, even as they continue to expand into interstellar space. The distance of objects such as NGC 6884 is typically more a matter of guesswork than direct observation, as the stars at their center are not Main Sequence stars, and have no "standard candle" to help us determine how bright they really are, and from that how far away they might be. In this case, studies of the expansion of the nebula (using HST images) by Palen et al yield distance estimates of 4 to 8 thousand light years; not a terribly precise value, but still better than nothing. Given that and the approximately 1.2 arcmin size of the outer ring, that structure is about 2 light years across; while the few arcsec apparent size of the "stellar" planetary corresponds to about a tenth of that value.

(20 arcmin wide?)

Per Dreyer, NGC 6886 (= Copeland, 1860 RA 20 06 29, NPD 70 25.7) is a "planetary nebula, stellar, equivalent to 10th magnitude". The position precesses to RA 20 12 42.5, Dec +19 59 22, dead on the star in question, so the identification is certain. Like most of Copeland's stellar planetaries, NGC 6886 is essentially indistinguishable from an ordinary star using ordinary methods of observation; but see NGC 6884 for a discussion of the "blink" method used by amateur observers to identify such objects, or NGC 6766 for a discussion of the spectroscopic method used by observers of the day.

3.2 by 1.3 arcmin

The second IC lists a corrected 1860 RA (per Bigourdan) of 20 07 01. The Crescent Nebula is an emission nebula caused by the collision of two waves of gaseous emissions by the "bright" (7th-magnitude) star near its center, WR 136. The star is an approximately 4.5 million year old Wolf-Rayet star of perhaps 40 to 80 solar masses. Wolf-Rayet stars are very massive, extremely hot stars (originally O-type Main Sequence stars) which are near the end of their lives. A few hundred thousand years ago the star swelled up to become a red super-giant, and ejected a few tenths of a solar mass of gas at about 20 thousand miles per hour. About 200 thousand years later, it heated up to several hundred thousand degrees, and began ejecting about a solar mass of super-heated gas per ten thousand years, at nearly 1% the speed of light (3 to 4 million miles per hour). As the faster moving, hotter gas reached the shower-moving, cooler gas previously released, it created a supersonic shock wave, causing the nebula to emit visible (primarily red H‘) light, as well as ultraviolet and X-radiation. The complex filamentary structure of the nebula is real, but its spherical structure is tissue-thin in comparison to its size. Only the surface of the structure is glowing; the hot gas streaming away from the star is essentially invisible. Within a few thousand years the current nebula will fade away, as its gas disperses into the surrounding space; but within a hundred thousand years, a new and even more spectacular nebula will form when the star supernovas. WR 136 and its nebula are about 4700 light years away. Given that and the approximately 18 by 12 arcmin apparent size of the nebula, NGC 6888 is about 25 light years across.

Below, a HST false-color image of a shock-heated portion of the nebula. The black and white visible-light image shows the region covered by the HST closeup. (Image Credits: NASA, Brian D. Moore, Jeff Hester, Paul Scowen (Arizona State University), Reginald Dufour (Rice University))

Below, a Chandra space telescope X-ray image of a region which includes the HST image above, superimposed on a ground-based image of the whole nebula. The X-radiation detected by Chandra (shown in false-color blue) represents gas shock-heated to about 2 million Fahrenheit degrees. (Image Credits: X-ray: NASA/UIUC/Y. Chu & R. Gruendl et al. Optical: SDSU/MLO/Y. Chu et al.)

0.9 by 0.7 arcmin

1.6 by 1.3 arcmin

Per Dreyer, NGC 6891 (= Copeland, 1860 RA 20 08 32, NPD 77 41.2) is a "planetary nebula, stellar, equivalent to 9.5 magnitude". The position precesses to RA 20 15 07.4, Dec +12 44 15, about 2 arcmin north northwest of the star in question, but there is nothing else nearby which in any way matches the description, so the identification is certain. Like many of Copeland's "stellar" planetary nebulae, the central portion of NGC 6891 looks very much like a star, but there is a faint outer ring visible in long-exposure photographs, which (as in the case of NGC 6884) was presumably ejected by the central star several thousand years ago, and is now fading from view; and even the inner region displays a complex structure in high-resolution images, such as the HST image below. The distance of planetary nebulae is typically more a matter of guesswork than direct observation, as the stars at their center are not Main Sequence stars, and provide no "standard candle" to help us determine how bright they really are. In the case of NGC 6891, the distance has been estimated from studies (by Palen et al) of the expansion of the nebula, as measured with HST images spaced over a period of about four years. The expansion rate for NGC 6891 turned out to be so slow that it could not be measured in the brief time involved; but comparison with the other objects studied suggests that it is at least 3000 light years away, as any closer distance should have yielded measurable results (closer distances making the nebula and its expansion rate appear larger).