The Saturn Nebula (also known as NGC 7009 or Caldwell 55) is a planetary nebula in the

constellation A constellation is an area on the celestial sphere in which a group of visible stars forms Asterism (astronomy), a perceived pattern or outline, typically representing an animal, mythological subject, or inanimate object. The origins of the e ...

Aquarius Aquarius may refer to: Astrology * Aquarius (astrology), an astrological sign * Age of Aquarius, a time period in the cycle of astrological ages Astronomy * Aquarius (constellation) * Aquarius in Chinese astronomy Arts and entertainment ...

. It appears as a greenish-yellowish hue in a small

amateur telescope ''Amateur Telescope Making'' (''ATM'') is a series of three books edited by Albert G. Ingalls between 1926 and 1953 while he was an associate editor at ''Scientific American''. The books cover various aspects of telescope construction and observ ...

. It was discovered by William Herschel on September 7, 1782, using a telescope of his own design in the garden at his home in

Datchet Datchet is a village and civil parish in the Royal Borough of Windsor and Maidenhead in Berkshire, England, located on the north bank of the River Thames. Historically part of Buckinghamshire, and the Stoke Hundred, the village was eventually tr ...

England England is a country that is part of the United Kingdom. It shares land borders with Wales to its west and Scotland to its north. The Irish Sea lies northwest and the Celtic Sea to the southwest. It is separated from continental Europe b ...

, and was one of his earliest discoveries in his sky survey. The nebula was originally a

low-mass star Star formation is the process by which dense regions within molecular clouds in The "medium" is present further soon.-->interstellar space

that ejected its layers into space, forming the nebula. The central star is now a bright

white dwarf star A white dwarf is a stellar core remnant composed mostly of electron-degenerate matter. A white dwarf is very dense: its mass is comparable to the Sun's, while its volume is comparable to the Earth's. A white dwarf's faint luminosity comes f ...

apparent magnitude Apparent magnitude () is a measure of the brightness of a star or other astronomical object observed from Earth. An object's apparent magnitude depends on its intrinsic luminosity, its distance from Earth, and any extinction of the object's li ...

11.5. The Saturn Nebula gets its name from its superficial resemblance to the planet Saturn with its rings nearly edge-on to the observer. It was so named by

Lord Rosse William Parsons, 3rd Earl of Rosse (17 June 1800 – 31 October 1867), was an Irish astronomer, naturalist, and engineer. He was president of the Royal Society (UK), the most important association of naturalists in the world in the nineteenth ...

in the 1840s, when telescopes had improved to the point that its Saturn-like shape could be discerned. William Henry Smyth said that the Saturn Nebula was one of Struve's nine "Rare Celestial Objects". The Saturn Nebula is a complex planetary nebula and contains many morphological and kinematic sub-systems in three dimensions. It includes a halo, jet-like streams, multiple shells, ansae ("handles"), and small-scale filaments and knots. The ansae are expanding non-radially from the central star. Although the ansae are most prominent in the Saturn Nebula, they are also visible in other planetary nebulae, including

NGC 3242 NGC 3242 (also known as the Ghost of Jupiter, eye nebula or Caldwell 59) is a Planetary nebula, planetary nebula located in the constellation Hydra (constellation), Hydra. William Herschel discovered the nebula on February 7, 1785, and catalogue ...

, NGC 6543 and

NGC 2371-2 NGC 2371-2 is a dual lobed planetary nebula located in the constellation Gemini. Visually, it appears like it could be two separate objects; therefore, two entries were given to the planetary nebula by John Louis Emil Dreyer in the New Genera ...

. The distance of the Saturn Nebula is not known precisely. estimates the distance to be 5,200 light-years (1.6 kpc). In 1963 O'Dell estimated it to be 3,900 light-years (1.2 kpc), which gives an approximate diameter of 0.5 light years for the object as a whole. The central star, a very hot bluish dwarf with a temperature of 55,000 K, from which the nebula is believed to originate, has an absolute magnitude of +1.5, which equates to a luminosity of about 20

solar luminosities The solar luminosity (), is a unit of radiant flux (Power (physics), power emitted in the form of photons) conventionally used by astronomers to measure the luminosity of stars, galaxy, galaxies and other celestial objects in terms of the output o ...

and a visual magnitude of 11.5. This strong ultraviolet irradiation from the central star creates the characteristic fluorescent green tint of the nebula via the radiation of doubly ionized oxygen. The object overall has a visual magnitude of 8 and a radial velocity of 28 miles per second towards the

Earth Earth is the third planet from the Sun and the only astronomical object known to harbor life. While large volumes of water can be found throughout the Solar System, only Earth sustains liquid surface water. About 71% of Earth's surfa ...

. The nebula is 1 degree west of the star

Nu Aquarii Nu Aquarii (ν Aqr, ν Aquarii) is the Bayer designation for a star in the equatorial constellation of Aquarius. With an apparent visual magnitude of 4.52, Nu Aquarii is visible to the naked eye. Its distance from Earth, as determined ...

. The central portion measures 25″ × 17″, while the outer shell extends to 41″ × 35″. The object is on many "best of" observing lists.RASC's Finest N.G.C. Objects

. NGC 7009 Lord Rosse.jpg, 1848 drawing of NGC 7009 by

. Looking at the Saturn Nebula in 3D.webm, This visualisation shows three-dimensional MUSE data of the nebula. File:NGC_7009_"Saturn_Nebula".jpg

Notes

References

External links

– NGC 7009: The Saturn Nebula * {{DEFAULTSORT:Saturn Nebula Planetary nebulae Aquarius (constellation) NGC objects Caldwell objects, 055b Astronomical objects discovered in 1782