Based on a recessional velocity 9765 km/sec, NGC 6350 is about 455 million light years away. Given that and its apparent size of 1.0 by 1.0 arcmin, it is about 130 thousand light years across.

NGC 6357 is an emission nebula associated with several clusters of stars recently formed, and still in the process of formation. One of the clusters, Pismis 24, contains a large number of very massive stars, one of which, Pismis 24-1, was thought to be the most massive known star, with perhaps two or three hundred solar masses; but as shown in the bottom image, it is actually a double (or even multiple) star, so each star is no more than 70 to 100 or so solar masses. Still, that is near the maximum theoretical mass for stars (about 100 to 150 solar masses), so stars of such mass are very rare (less than one in ten thousand for new stars, and less than one in a million for all stars, since the massive ones don't last very long). The nebula is about a degree across, and given its probable distance of 8000 light years, must be well over 100 light years across.

Below, a HST closeup of the region above. At top, a massive young star is heating and blowing away the clouds of gas and dust still surrounding it and its (mostly unseen) companions. Pismis 24 is the group of bright stars scattered below the brightly glowing clouds. (Image Credits: ESA and J. M. Apellániz (IAA, Spain), NASA. Acknowledgement: Davide De Martin (ESA/Hubble))

Normally, an NGC object with a double listing should be referred to by the number corresponding to its earliest discovery; but in this case the identity of the two listings was not recognized for over a century, so it is most appropriate to refer to this galaxy as NGC 6363. For a history of the confusion and its eventual unraveling, see NGC 6138.

The Arp Atlas listing as a spiral galaxy with one heavy arm is reasonable, but wrong. On Arp's original plate, the edge-on galaxy appears to be part of the face-on spiral, as its position is where an extension of the face-on galaxy's spiral arm would be. However, the better images below show that it is actually a separate galaxy. The face-on galaxy's recessional velocity of 8035 km/sec implies that it is 375 million light years away, in reasonable agreement with redshift-independent distance estimates of 390 to 410 million light years. The edge-on galaxy's recessional velocity of 8495 km/sec implies that it is 395 million light years away. The difference in radial velocity (and implied distance) is small enough that the galaxies' peculiar (non-Hubble-expansion) velocities may be a significant part of the difference, so they may be closer than stated, gravitationally bound, and not just a chance alignment. However, the lack of any obvious distortion in either galaxy suggests that although close to each other in comparison to their distance from us, they may be too far apart to have any significant gravitational interaction. Either way, their apparent sizes (1.1 by 0.2 arcmin for the edge-on galaxy, and 1.15 by 0.85 arcmin for the face-on) imply that each is about 125 thousand light years across. (Note: NGC 6365A (the face-on galaxy) is a Seyfert galaxy (type Sy1).)

The Little Ghost Nebula is a planetary nebula between two and five thousand light years away. Planetary nebulae are clouds of gas blown off red giant stars in the last stages of their life. If enough gas is ejected, what is left of the star is unable to compress the core of the star enough to produce any further nuclear reactions, and the star collapses to form a white dwarf (the star near the center of the nebula). Prior to the collapse, the star might have been several hundred million miles across. Afterwards, it is less than ten thousand miles across, and as a result, has a density close to a million times the density of water. The central more or less circular core of the nebula is a light year or two across, while the fainter outer regions cover about twice that distance. Both regions are expanding at about 15 miles per second, and will dissipate into interstellar space and fade from view over the next ten thousand or so years, partly because of their gradually decreasing density, and partly because the white dwarf is currently very hot, and emitting large amounts of ultraviolet radiation, which is energizing the nebula. As the white dwarf cools, its ultraviolet radiation will diminish, which would cause the nebula to fade from view, even if it didn't dissipate. Note concerning the HST image below: To bring out details not visible in a true-color image, the HST image below uses "false-color" blue, green and red colors to represent radiation from double ionized oxygen, and singly ionized hydrogen and nitrogen atoms, respectively. If the nebula were observed with a large enough telescope to see some hint of color, it would actually appear to be a pale greenish-gray; gray, because even bright planetary nebulae are too faint to be seen in color, and greenish, because our eyes are most sensitive to that type of light.

The second IC adds the description (per DeLisle Stewart) "extremely faint, hazy star only". Based on a recessional velocity of 5365 km/sec, NGC 6398 is about 250 million light years away. Given that and its apparent size of 2.0 by 1.7 arcmin, it is about 145 thousand light years across.