William Herschel discovered NGC 5142 = H III-403 = h1600, along with NGC 5141, on 1 May 1785 (sweep 405). JH made two observations and recorded on sweep 331 "pF; R; vsbM to a star."

400/500mm - 17.5" faint, small, small bright core, stellar nucleus, elongated ~N-S. Forms a pair with NGC 5141 2.3' SW. NGC 5143 2.3' N was not seen.

Notes by Steve Gottlieb