William Herschel discovered NGC 5546 = H III-551 = h1770 on 1 May 1786 (sweep 560) and recorded "Two [with III-552 = NGC 5549], both eF and vS. The place is that of the last; a little inaccurate. I would not stay to verify it properly. So that there remains some little doubt; the 1st precedes the last about 3 or 4'." His position is within 1.5' of UGC 9156, which is identified as NGC 5549, but there no object preceding by 3'-4'. In his 1912 update of WH's catalogues, Dreyer suggests this observation may refer to NGC 5542 and NGC 5546, which differ by the required amount.

On a second observation on 12 May 1793 (sweep 1042), H's position for III-551 is 2.4' southwest of UGC 9148! So, his two sweeps refer to different objects. JH also made two observations of UGC 9148 and measured an accurate position, but he was uncertain if this was his father's object and gave them both GC designations. Dreyer combined both GC numbers in the NGC.

400/500mm - 17.5" (7/17/01): brightest in a small trio and forming a right angle with NGC 5542 4.0' W and NGC 5543 5.5' NNW. Moderately bright, fairly small, round, 1.0' diameter. Broad concentration to a brighter core.

17.5" (5/10/91): fairly faint, fairly small, round, prominent bright core, stellar nucleus. Brightest in a group with NGC 5542 4' W and NGC 5543 5' NNW.

Notes by Steve Gottlieb