A nebula is a distinct luminescent part of interstellar medium, which can consist of ionized, neutral, or molecular hydrogen and also cosmic dust. Nebulae are often star-forming regions, such as in the "Pillars of Creation" in the Eagle Nebula. In these regions, the formations of gas, dust, and other materials "clump" together to form denser regions, which attract further matter and eventually become dense enough to form stars. The remaining material is then thought to form planets and other planetary system objects.
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.
Hoag's Object is an unusual ring galaxy in the constellation of Serpens Caput. It is named after Arthur Hoag, who discovered it in 1950 and identified it as either a planetary nebula or a peculiar galaxy. The galaxy has a D25 isophotal diameter of 45.41 kiloparsecs (148,000 light-years).
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.
Messier 100 is a grand design intermediate spiral galaxy in the southern part of the mildly northern Coma Berenices. It is one of the brightest and largest galaxies in the Virgo Cluster and is approximately 55 million light-years from our galaxy, its diameter being 107,000 light years, and being about 60% as large. It was discovered by Pierre Méchain in 1781 and 29 days later seen again and entered by Charles Messier in his catalogue "of nebulae and star clusters". It was one of the first spiral galaxies to be discovered, and was listed as one of fourteen spiral nebulae by Lord William Parsons of Rosse in 1850. NGC 4323 and NGC 4328 are satellite galaxies of M100; the former is connected with it by a bridge of luminous matter.
An astronomical object, celestial object, stellar object or heavenly body is a naturally occurring physical entity, association, or structure that exists within the observable universe. In astronomy, the terms object and body are often used interchangeably. However, an astronomical body or celestial body is a single, tightly bound, contiguous entity, while an astronomical or celestial object is a complex, less cohesively bound structure, which may consist of multiple bodies or even other objects with substructures.
An H II region or HII region is a region of interstellar atomic hydrogen that is ionized. It is typically in a molecular cloud of partially ionized gas in which star formation has recently taken place, with a size ranging from one to hundreds of light years, and density from a few to about a million particles per cubic centimetre. The Orion Nebula, now known to be an H II region, was observed in 1610 by Nicolas-Claude Fabri de Peiresc by telescope, the first such object discovered.
The Whirlpool Galaxy, also known as Messier 51a (M51a) or NGC 5194, is an interacting grand-design spiral galaxy with a Seyfert 2 active galactic nucleus. It lies in the constellation Canes Venatici, and was the first galaxy to be classified as a spiral galaxy. It is 7.22 megaparsecs away and 23.58 kiloparsecs (76,900 ly) in diameter.
Messier 58 is an intermediate barred spiral galaxy with a weak inner ring structure located within the constellation Virgo, approximately 68 million light-years away from Earth. It was discovered by Charles Messier on April 15, 1779 and is one of four barred spiral galaxies that appear in Messier's catalogue. M58 is one of the brightest galaxies in the Virgo Cluster. From 1779 it was arguably the farthest known astronomical object until the release of the New General Catalogue in the 1880s and even more so the publishing of redshift values in the 1920s.
The Little Dumbbell Nebula, also known as Messier 76, NGC 650/651, the Barbell Nebula, or the Cork Nebula, is a planetary nebula in the northern constellation of Perseus. It was discovered by Pierre Méchain in 1780 and included in Charles Messier's catalog of comet-like objects as number 76. It was first classified as a planetary nebula in 1918 by the astronomer Heber Doust Curtis. However, others might have previously recognized it as a planetary nebula; for example, William Huggins found its spectrum indicated it was a nebula ; and Isaac Roberts in 1891 suggested that M76 might be similar to the Ring Nebula (M57), as seen instead from the side view.
Messier 90 is an intermediate spiral galaxy exhibiting a weak inner ring structure about 60 million light-years away[a] in the constellation Virgo. It was discovered by Charles Messier in 1781.
The Owl Nebula is a planetary nebula approximately 2,030 light years away in the constellation Ursa Major. Estimated to be about 8,000 years old, it is approximately circular in cross-section with a faint internal structure. It was formed from the outflow of material from the stellar wind of the central star as it evolved along the asymptotic giant branch. The nebula is arranged in three concentric shells, with the outermost shell being about 20–30% larger than the inner shell. The owl-like appearance of the nebula is the result of an inner shell that is not circularly symmetric, but instead forms a barrel-like structure aligned at an angle of 45° to the line of sight.
IC 3568 is a planetary nebula that is 1.3 kiloparsecs away from Earth in the constellation of Camelopardalis. It is a relatively young nebula and has a core diameter of only about 0.4 light years. It was dubbed the Lemon Slice Nebula by Jim Kaler, due to its appearance in one false-colour image from the Hubble Space Telescope. The Lemon Slice Nebula is one of the most simple nebulae known, with an almost perfectly spherical morphology. The core of the nebula does not have a distinctly visible structure in formation and is mostly composed of ionized helium. A faint halo of interstellar dust surrounds the nebula. The central star of the planetary nebula is an O-type star with a spectral type of O(H)3.
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.
The Abell Catalog of Planetary Nebulae was created in 1966 by George O. Abell and was composed of 86 entries thought to be planetary nebulae that were collected from discoveries, about half by Albert George Wilson and the rest by Abell, Robert George Harrington, and Rudolph Minkowski. All were discovered before August 1955 as part of the National Geographic Society – Palomar Observatory Sky Survey on photographic plates created with the 48-inch (1.2 m) Samuel Oschin telescope at Mount Palomar. Four are better known from previous catalogs: Abell 50 is NGC 6742, Abell 75 is NGC 7076, Abell 37 is IC 972, and Abell 81 is IC 1454. Another four were later rejected as not being planetaries: Abell 11, Abell 32, Abell 76, and Abell 85. Another three were also not included in the Strasbourg-ESO Catalogue of Galactic Planetary Nebulae (SEC): Abell 9, Abell 17, and Abell 64. Planetaries on the list are best viewed with a large aperture telescope and an OIII filter.
NGC 2242 is a planetary nebula in the constellation Auriga. It was discovered by Lewis A. Swift on November 24, 1886, and was thought to be a galaxy until a study published in 1987 showed it to be a planetary nebula. The nebula is located about 6,500 light-years away, and about 1,600 light-years above the galactic plane.
IC 5332, also known as PGC 71775 is an intermediate spiral galaxy about 30 million light-years away in the constellation Sculptor. IC 5332 is a delicate spiral galaxy that is unusually faint and beautifully symmetrical. As viewed from earth it is nearly face on. It has a very small central bulge and open spiral arms accounting for its classification (SABc). The galaxy lies in the direction of the galactic south pole.
NGC 7020 is a barred lenticular galaxy located about 140 million light-years away in the constellation Pavo. NGC 7020 was discovered by astronomer John Herschel on August 31, 1836.
NGC 3313 is a large barred spiral galaxy located about 55 megaparsecs away in the constellation Hydra. It was discovered by astronomer Ormond Stone in 1886 and is an outlying member of the Hydra Cluster.
