NGC 6445, also known as the Little Gem Nebula or Box Nebula, is a

planetary nebula A planetary nebula is a type of emission nebula consisting of an expanding, glowing shell of ionized gas ejected from red giant stars late in their lives. The term "planetary nebula" is a misnomer because they are unrelated to planets. The ...

in the constellation

Sagittarius Sagittarius ( ) may refer to: *Sagittarius (constellation) *Sagittarius (astrology), a sign of the Zodiac * Sagittarius of Gap, a 6th century bishop *Sagittarius A*, the supermassive black hole at the center of the Milky Way galaxy Ships *'' S ...

. It was discovered by

William Herschel Frederick William Herschel ( ; ; 15 November 1738 – 25 August 1822) was a German-British astronomer and composer. He frequently collaborated with his younger sister and fellow astronomer Caroline Herschel. Born in the Electorate of Hanover ...

on May 28, 1786. The distance of NGC 6445 is estimated to be slightly more than 1,000 parsecs based on the

parallax Parallax is a displacement or difference in the apparent position of an object viewed along two different sightline, lines of sight and is measured by the angle or half-angle of inclination between those two lines. Due to perspective (graphica ...

measured by

Gaia In Greek mythology, Gaia (; , a poetic form of ('), meaning 'land' or 'earth'),, , . also spelled Gaea (), is the personification of Earth. Gaia is the ancestral mother—sometimes parthenogenic—of all life. She is the mother of Uranus (S ...

, which was measured at mas.

Characteristics

NGC 6445 has been classified as a bipolar planetary nebula. Its He/H and N/O abundance ratios are consistent with the Type I definition. In optical images, NGC 6445 features a bright, central ring-shaped morphology and open bipolar lobes; the outer envelope emission of NGC 6445 is IIdominant. Wide-field optical images obtained by the

Nordic Optical Telescope The Nordic Optical Telescope (NOT) is an astronomical telescope located at Roque de los Muchachos Observatory, La Palma in the Canary Islands. The telescope saw first light in 1988, and was officially inaugurated during September 1989. Regular o ...

(NOT) Andalucía Faint Object Spectrograph and Camera (ALFOSC) show that NGC 6445 has an irregularly shaped central region with a size of ~40"×50", where the IIIemission dominates, while the IIemission is much more extended and defines an overall bipolar morphology. This article contains quotations from this source, which is available under th
Creative Commons Attribution 3.0 Unported (CC BY 3.0)
license. At distance, NGC 6445 is 4 light years across and is among the largest known.

Observation

NGC 6445 lies 2.1° southwest from the open cluster

Messier 23 Messier 23, also known as NGC 6494, is an open cluster of stars in the northwest of the southern constellation of Sagittarius. It was discovered by Charles Messier in 1764. It can be found in good conditions with binoculars or a modestly sized t ...

. NGC 6445 can be located by star hopping from Messier 23, by firstly locating an arc of 7th and 8th magnitude stars one degree southwest of M23, with the nebula lying 5 arcminutes west of an 8th magnitude star that lies 40 arcminutes west of the southernmost star of the arc. The globular cluster NGC 6440 lies 23 arcminutes to the south and both objects can be seen in a wide field eyepiece. In low magnification the nebula appears like a fuzzy star and higher magnifications reveal its rectangular disk. The planetary nebula is included in the

Herschel 400 Catalogue The Herschel 400 catalogue is a subset of William Herschel, William Herschel's original ''Catalogue of Nebulae and Clusters of Stars'', selected by Brenda F. Guzman (Branchett), Lydel Guzman, Paul Jones, James Morris, Peggy Taylor and Sara Saey of ...

References

External links

{{Ngc65 Planetary nebulae Sagittarius (constellation) 6445 category:Discoveries by William Herschel