Sagittarius is one of the constellations of the zodiac and is located in the Southern celestial hemisphere. It is one of the 48 constellations listed by the 2nd-century astronomer Ptolemy and remains one of the 88 modern constellations. Its old astronomical symbol is (♐︎). Its name is Latin for "archer". Sagittarius is commonly represented as a centaur drawing a bow. It lies between Scorpius and Ophiuchus to the west and Capricornus and Microscopium to the east.
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.
An emission nebula is a nebula formed of ionized gases that emit light of various wavelengths. The most common source of ionization is high-energy ultraviolet photons emitted from a nearby hot star. Among the several different types of emission nebulae are H II regions, in which star formation is taking place and young, massive stars are the source of the ionizing photons; and planetary nebulae, in which a dying star has thrown off its outer layers, with the exposed hot core then ionizing them.
The Boomerang Nebula is a protoplanetary nebula located 1,200 light-years away from Earth in the constellation Centaurus. It is also known as the Bow Tie Nebula and catalogued as LEDA 3074547. The nebula's temperature is measured at 1 K making it the coolest natural place currently known in the Universe.
The Cat's Eye Nebula is a planetary nebula in the northern constellation of Draco, discovered by William Herschel on February 15, 1786. It was the first planetary nebula whose spectrum was investigated by the English amateur astronomer William Huggins, demonstrating that planetary nebulae were gaseous and not stellar in nature. Structurally, the object has had high-resolution images by the Hubble Space Telescope revealing knots, jets, bubbles and complex arcs, being illuminated by the central hot planetary nebula nucleus (PNN). It is a well-studied object that has been observed from radio to X-ray wavelengths.
The Calabash Nebula, also known as the Rotten Egg Nebula or by its technical name OH 231.84 +4.22, is a protoplanetary nebula (PPN) 1.4 light years long and located some 5,000 light years from Earth in the constellation Puppis. The name "Calabash Nebula" was first proposed in 1989 in an early paper on its expected nebular dynamics, based on the nebula's appearance. The Calabash is almost certainly a member of the open cluster Messier 46, as it has the same distance, radial velocity, and proper motion. The central star is QX Puppis, a binary composed of a very cool Mira variable and an A-type main-sequence star.
The Stingray Nebula is the youngest-known planetary nebula, having appeared in the 1980s. The nebula is located in the direction of the southern constellation Ara, and is located 18,000 light-years away. Although it is some 130 times the size of the Solar System, the Stingray Nebula is only about one tenth the size of most other known planetary nebulae. The central star of the nebula is the fast-evolving star SAO 244567. Until the early 1970s, it was observed on Earth as a preplanetary nebula in which the gas had not yet become hot and ionized.
Minkowski 2-9, abbreviated M2-9 is a planetary nebula that was discovered by Rudolph Minkowski in 1947. It is located about 2,100 light-years away from Earth in the direction of the constellation Ophiuchus. This bipolar nebula takes the peculiar form of twin lobes of material that emanate from a central star. Astronomers have dubbed this object as the Twin Jet Nebula because of the jets believed to cause the shape of the lobes. Its form also resembles the wings of a butterfly. The nebula was imaged by the Hubble Space Telescope in the 1990s.
NGC 5189 is a planetary nebula in the constellation Musca. It was discovered by James Dunlop on 1 July 1826, who catalogued it as Δ252. For many years, well into the 1960s, it was thought to be a bright emission nebula. It was Karl Gordon Henize in 1967 who first described NGC 5189 as quasi-planetary based on its spectral emissions.
NGC 7027, also known as the Jewel Bug Nebula or the Magic Carpet Nebula, is a very young and dense planetary nebula located around 3,000 light-years from Earth in the constellation Cygnus. Discovered in 1878 by Édouard Stephan using the 800 mm (31 in) reflector at Marseille Observatory, it is one of the smallest planetary nebulae and by far the most extensively studied.
NGC 3132 is a bright and extensively studied planetary nebula in the constellation Vela. Its distance from Earth is estimated at 613 pc or 2,000 light-years.
M1-92, also known as Minkowski’s Footprint or the Footprint Nebula, is a bipolar protoplanetary nebula in the constellation of Cygnus. It is a type of reflection nebula, visible only by light reflected from the central star. The central star is not yet a white dwarf but is quickly becoming one. In a few thousand years the star will be hot enough to emit vast quantities of ultraviolet radiation that will ionize the nebula surrounding it, making it a fully fledged planetary nebula.
NGC 2440 is a planetary nebula, one of many in our galaxy. Its central star, HD 62166, is possibly the hottest known white dwarf, about 400,000°F(200,000°C). The nebula is situated in the constellation Puppis.
NGC 1316 is a lenticular galaxy about 60 million light-years away in the constellation Fornax. It is a radio galaxy and at 1400 MHz is the fourth-brightest radio source in the sky.
NGC 6302 is a bipolar planetary nebula in the constellation Scorpius. The structure in the nebula is among the most complex ever seen in planetary nebulae. The spectrum of Butterfly Nebula shows that its central star is one of the hottest stars known, with a surface temperature in excess of 250,000 degrees Celsius, implying that the star from which it formed must have been very large.
NGC 6751, also known as the Glowing Eye Nebula, is a planetary nebula in the constellation Aquila. It is estimated to be about 6,500 light-years away.
NGC 2080, also known as the Ghost Head Nebula, is a star-forming region and emission nebula to the south of the 30 Doradus (Tarantula) nebula, in the southern constellation Dorado. It belongs to the Large Magellanic Cloud, a satellite galaxy to the Milky Way, which is at a distance of 168,000 light years. NGC 2080 was discovered by John Frederick William Herschel in 1834. The Ghost Head Nebula has a diameter of 50 light-years and is named for the two distinct white patches it possesses, called the "eyes of the ghost". The western patch, called A1, has a bubble in the center which was created by the young, massive star it contains. The eastern patch, called A2, has several young stars in a newly formed cluster, but they are still obscured by their originating dust cloud. Because neither dust cloud has dissipated due to the stellar radiation, astronomers have deduced that both sets of stars formed within the past 10,000 years. These stars together have begun to create a bubble in the nebula with their outpourings of material, called stellar wind.
A bipolar nebula is a type of nebula characterized by two lobes either side of a central star. About 10-20% of planetary nebulae are bipolar.
NGC 5315 is a planetary nebula in the southern constellation Circinus. Of apparent magnitude 9.8 around a central star of magnitude 14.2, it is located 5.2 degrees west-southwest of Alpha Circini. It is only visible as a disc at magnifications over 200-fold. The nebula was discovered by astronomer Ralph Copeland in 1883. The central star has a stellar class of WC4 and is hydrogen deficient with an effective temperature of 76-79 kK. The distance to this nebula is not known accurately, but is estimated to be around 6.5 kilolight-years.
NGC 3242 is a planetary nebula located in the constellation Hydra.
