Edward Pickering discovered NGC 6644 on 13 Jul 1880 (Sidereal Messenger, Oct 1882) with the 15-inch refractor at Harvard College Observatory. This was first of 17 planetaries he found using a direct-vision spectroscope (15 new discoveries in the NGC). Pickering noted in The Observatory (1881) that "its disk is so small that it can scarcely be detected with an ordinary eyepiece even if brought into the field of view."

Based on Crossley photographs taken at Lick, Curtis (1918) reported "this object is indistinguishable from a star on the Crossley negatives, but visual observations made by Mr. Moore and Aitken with the 36-inch refractor show that it is a minute disk 2" to 3" in diameter."

400/500mm - 17.5" (8/1/86): bright bluish "star" at 105x that brightens dramatically with OIII blinking. A mag 12 star (good for blinking comparison) is 1.0' N. At 286x, a small disc is visible about 3" or 4" diameter. Estimate V = 11.0.

Notes by Steve Gottlieb