Based on a recessional velocity of 3720 km/sec, NGC 6750 is about 175 million light years away. Given that and its apparent size of 1.0 by 0.6 arcmin, it is about 50 thousand light years across.

Per Dreyer, NGC 6766 (= Pickering (HN 53), 1860 RA 19 05 57, NPD 43 57.7) is a "planetary nebula, stellar". The RA is off by an hour (it should be 20 05 57), but Dreyer never learned of the error, and as a result NGC 6766 was thought to be lost or nonexistent for more than a century. However, it turns out that Pickering published a corrected position (in HA 60) after the last NGC/IC catalog was published, and it was just bad luck (and the difficulty of searching through mountains of old and presumably obsolete papers) that no one noticed that correction (or Thomas Espin's 1911 paper, in which he quotes Pickering as having corrected the position) until (per Corwin) Dave Riddle finally found the answer to the puzzle. In any event, the huge error in the NGC position made it inevitable that Copeland's later observation would end up with a completely different listing, even though Pickering's corrected position (and description) was identical. Note: Corwin mentions Pickering's ingenious method of discovering "stellar" planetaries, which are indistinguishable from stars by ordinary methods of observation. He would place a prism in the light path of his telescope, which turned stellar images into a blur of various colors (or more accurately, given their faintness, into a linear blur of a pale grayish color) corresponding to their continuous spectra, but left planetary nebulae, which emit significant amounts of light at only one or two wavelengths, as apparently stellar objects. In other words, the stars became nebular blurs, and the planetary nebulae remained starlike; so that the appearance was exactly backwards from the reality. This provided an easy way to quickly distinguish planetary nebulae from stars, albeit one that is beyond the reach of most amateur telescopes, which (until the advent of CCD cameras) would produce spectra far too faint to see. Since NGC 6766 is identical to NGC 6884, see that entry for images and a discussion of the physical nature of the object.