The Ring Nebula is a planetary nebula in the northern constellation of Lyra.[C] Such a nebula is formed when a star, during the last stages of its evolution before becoming a white dwarf, expels a vast luminous envelope of ionized gas into the surrounding interstellar space.
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 Trifid Nebula is an H II region in the north-west of Sagittarius in a star-forming region in the Milky Way's Scutum–Centaurus Arm. It was discovered by Charles Messier on June 5, 1764. Its name means 'three-lobe'. The object is an unusual combination of an open cluster of stars, an emission nebula, a reflection nebula, and a dark nebula. Viewed through a small telescope, the Trifid Nebula is a bright and peculiar object, and is thus a perennial favorite of amateur astronomers.
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 Eagle Nebula is a young open cluster of stars in the constellation Serpens, discovered by Jean-Philippe de Cheseaux in 1745–46. Both the "Eagle" and the "Star Queen" refer to visual impressions of the dark silhouette near the center of the nebula, an area made famous as the "Pillars of Creation" imaged by the Hubble Space Telescope. The nebula contains several active star-forming gas and dust regions, including the aforementioned Pillars of Creation. The Eagle Nebula lies in the Sagittarius Arm of the Milky Way.
The Horsehead Nebula is a small dark nebula in the constellation Orion. The nebula is located just to the south of Alnitak, the easternmost star of Orion's Belt, and is part of the much larger Orion molecular cloud complex. It appears within the southern region of the dense dust cloud known as Lynds 1630, along the edge of the much larger, active star-forming H II region called IC 434.
The Carina Nebula or Eta Carinae Nebula is a large, complex area of bright and dark nebulosity in the constellation Carina, located in the Carina–Sagittarius Arm of the Milky Way galaxy. The nebula is approximately 8,500 light-years (2,600 pc) from Earth.
The Crescent Nebula is an emission nebula in the constellation Cygnus, about 5000 light-years away from Earth. It was discovered by William Herschel in 1792. It is formed by the fast stellar wind from the Wolf-Rayet star WR 136 colliding with and energizing the slower moving wind ejected by the star when it became a red giant around 250,000 to 400,000 years ago. The result of the collision is a shell and two shock waves, one moving outward and one moving inward. The inward moving shock wave heats the stellar wind to X-ray-emitting temperatures.
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.
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.
The Veil Nebula is a cloud of heated and ionized gas and dust in the constellation Cygnus.
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.
NGC 2174 is an H II emission nebula located in the constellation Orion and is associated with the open star cluster NGC 2175. It was discovered on 6 February 1877 by French astronomer Édouard Stephan. It is thought to be located about 6,400 light-years away from Earth. The nebula may have formed through hierarchical collapse.
NGC 2022 is a planetary nebula in the equatorial constellation of Orion, located at a distance of 8.21 kilolight-years from the Sun. It was first observed by William Herschel on December 28, 1785, who described it as: considerably bright, nearly round, like a star with a large diameter, like an ill-defined planetary nebula. In medium-sized amateur telescopes it looks like a small grayish patch of light. It is not very bright but it is still easy to spot it in the eyepiece. Even in a telescope as small as 80mm it can just be seen using a narrowband filter such as an OIII filter as a 'fuzzy' star. The object has the shape of a prolate spheroid with a major to minor axis ratio of 1.2, an apparent size of 28″, and a halo extending out to 40″, which is about the angular diameter of Jupiter as seen from Earth.
NGC 2244 is an open cluster in the Rosette Nebula, which is located in the constellation Monoceros. This cluster has several O-type stars, super hot stars that generate large amounts of radiation and stellar wind.
IC 5146 is a reflection/emission nebula and Caldwell object in the constellation Cygnus. The NGC description refers to IC 5146 as a cluster of 9.5 mag stars involved in a bright and dark nebula. The cluster is also known as Collinder 470. It shines at magnitude +10.0/+9.3/+7.2. Its celestial coordinates are RA 21h 53.5m, dec +47° 16′. It is located near the naked-eye star Pi Cygni, the open cluster NGC 7209 in Lacerta, and the bright open cluster M39. The cluster is about 4,000 ly away, and the central star that lights it formed about 100,000 years ago; the nebula is about 12 arcmins across, which is equivalent to a span of 15 light years.
NGC 3324 is an open cluster in the southern constellation Carina, located northwest of the Carina Nebula (NGC 3372) at a distance of 9,100 ly (2,800 pc) from Earth. It is closely associated with the emission nebula IC 2599, also known as Gum 31. The two are often confused as a single object, and together have been nicknamed the "Gabriela Mistral Nebula" due to its resemblance to the Chilean poet. NGC 3324 was first catalogued by James Dunlop in 1826.
An astronomical filter is a telescope accessory consisting of an optical filter used by amateur astronomers to simply improve the details and contrast of celestial objects, either for viewing or for photography. Research astronomers, on the other hand, use various band-pass filters for photometry on telescopes, in order to obtain measurements which reveal objects' astrophysical properties, such as stellar classification and placement of a celestial body on its Wien curve.
Abell 31 is an ancient planetary nebula in the constellation of Cancer. It is estimated to be about 2,000 light years away. Although it is one of the largest planetary nebulae in the sky, it is not very bright. The central star of the planetary nebula is a white dwarf with a spectral type of DAO. The white dwarf is the dead remains of a star that existed but had died leaving behind Abell 31 and the white dwarf.
