Little Gem — Planetary Nebula in Sagittarius

NGC 6445 is a small, relatively bright planetary nebula in Sagittarius, about 4,500 light-years away, popularly called the 'Little Gem Nebula' for its compact, jewel-like appearance. The nebula is a bipolar planetary with a distinctive boxy or rectangular outline at its brightest inner core and fainter outer lobes in a characteristic butterfly pattern. Its central star is a hot white dwarf that has shed two successive shells of gas, producing the layered structure visible in deep images. NGC 6445 lies in a richly populated star field not far from the globular cluster M23.

A fine high-power target. At magnitude 11 it is within reach of 4-inch telescopes, but the nebula is small (about 45 arcseconds across) so magnifications of 200x or more are needed to see it as more than a fuzzy star. An 8- to 10-inch telescope at 250-300x under dark skies shows a clearly elongated, slightly rectangular shape — the 'gem' nickname comes from this compact boxiness. An OIII or UHC filter sharpens contrast. The globular cluster M23 lies about 40 arcminutes to the southeast and makes a natural hop-off point. Best observed June through September.

Discovered by William Herschel on May 28, 1786, during his great survey of the southern summer sky. Herschel described it as 'a planetary nebula, very small, extremely bright.' Its bipolar nature was not apparent in 19th-century observations; the butterfly structure was first mapped photographically in the early 20th century and has been refined by deep imaging with modern CCDs.