Saturn Nebula

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The Saturn Nebula (NGC 7009) is a small but fairly bright planetary nebula found in Aquarius constellation, about a degree west of the star Nu Aquarii. The nebula has an apparent magnitude of 8.0 and lies at an estimated distance between 2,000 and 4,000 light years from Earth. It was named the Saturn Nebula by Lord Rosse in 1840s, who noted its resemblance to the planet, with its rings appearing almost edge-on when seen from Earth.

The Saturn Nebula has an apparent size of 41″ by 35″, which translates into a linear radius between 0.2 and 0.4 light years, depending on the nebula’s exact distance, which is uncertain. The most recent estimates place it at 5,000 light years. The nebula’s central region measures 25″ by 17″.

Saturn Nebula,NGC 7009

The spectacular planetary nebula NGC 7009, or the Saturn Nebula, emerges from the darkness like a series of oddly-shaped bubbles, lit up in glorious pinks and blues. This colourful image was captured by the powerful MUSE instrument on ESO’s Very Large Telescope (VLT), as part of a study which mapped the dust inside a planetary nebula for the first time. Image: ESO/J. Walsh, September 2017

The nebula was formed when a low-mass star expelled its outer layers, which are now illuminated by strong ultraviolet irradiation from the remnant of the progenitor star, a bright white dwarf with a temperature of 55,000 K and a visual magnitude of 11.5. The central star has an absolute magnitude of +1.5, which translates into a luminosity about 20 times that of the Sun. The nebula is moving toward us at a radial velocity of 28 miles per second.

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Saturn Nebula, image: Judy Schmidt

The nebula has a complex structure consisting of a number of sub-systems, including jet-like streams, several shells, filaments, knots, ansae and a halo. The ansae (handles of low-density gas protruding from either side of the disk, spanning 41 arc seconds) are particularly striking in this nebula, but have also been observed in other planetary nebulae, including the Cat’s Eye Nebula (NGC 6543) in Draco constellation, the Ghost of Jupiter (NGC 3242) in Hydra, and the Gemini Nebula, sometimes also known as the Peanut Nebula (NGC 2371-2), in Gemini.

saturn nebula,cat's eye nebula,ngc 7662,ngc 6826

This gallery shows four planetary nebulas from the first systematic survey of such objects in the solar neighborhood made with NASA’s Chandra X-ray Observatory. The planetary nebulas shown here are NGC 6543 (aka the Cat’s Eye), NGC 7662, NGC 7009 and NGC 6826. X-ray emission from Chandra is colored purple and optical emission from the Hubble Space Telescope is colored red, green and blue. A planetary nebula is a phase of stellar evolution that the sun should experience several billion years from now, when it expands to become a red giant and then sheds most of its outer layers, leaving behind a hot core that contracts to form a dense white dwarf star. A wind from the hot core rams into the ejected atmosphere, creating the shell-like filamentary structures seen with optical telescopes. The diffuse X-ray emission is caused by shock waves as the wind collides with the ejected atmosphere. The properties of the X-ray point sources in the center of about half of the planetary nebulas suggest that many central stars responsible for ejecting planetary nebulas have companion stars. Image: Chandra X-ray Observatory Center, Smithsonian Institution @ Flickr Commons

The Saturn Nebula can be seen in small amateur telescopes and appears as a hazy greenish or yellowish patch. 10-inch telescopes will reveal the ansae under good viewing conditions. The nebula lies in the western part of Aquarius, just west of Nu Aquarii and 2 degrees northeast of the asterism Messier 73.

Saturn Nebula sketched by William Parsons, 3rd Earl of Rosse

The nebula was discovered by William Herschel on September 7, 1782, who used his own home-built telescope to observe this area of the sky from his home in Datchet, England. NGC 7009 was one of the first objects he discovered. Herschel himself coined the term planetary nebula because, at the time, he believed that these nebulae were contracting clouds of material around young stars, which would eventually form planets in the stars’ orbit.

The Saturn Nebula was recently studied by the Multi Unit Spectroscopic Explorer (MUSE) instrument, installed at the Very Large Telescope (VLT) of the European Southern Observatory’s (ESO) Paranal Observatory in Chile. ESO researchers were able to accurately map the nebula in order to better understand its structure.

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Saturn Nebula by the Hubble Space Telescope – image: Bruce Balick (University of Washington), Jason Alexander (University of Washington), Arsen Hajian (U.S. Naval Observatory), Yervant Terzian (Cornell University), Mario Perinotto (University of Florence, Italy), Patrizio Patriarchi (Arcetri Observatory, Italy), NASA/ESA

The team discovered a wave-like feature in the dust, which is typically evenly distributed throughout the nebula. However, the rim of the Saturn Nebula’s inner shell has a distinct lack of dust. This has led astronomers to speculate that the dust is being destroyed in this part of the nebula, either by a shockwave (in the form of nebula’s expanding inner shell) smashing into it and destroying it or a shockwave causing a strong heating effect that evaporates the dust. By using MUSE to map planetary nebulae’s complex structures, astronomers are hoping to shed some light on the role that dust and gas play in the lives and deaths of low-mass stars, as well as on the ways that the complex structures of these nebulae are formed.

Saturn Nebula – NGC 7009

Constellation: Aquarius
Right ascension: 21h 04m 10.877s
Declination: -11° 21’ 48.25”
Apparent size: 41″ × 35″
Radius: 0.2 to 0.4 light years
Distance: 2,000 – 4,000 light years
Apparent magnitude: 8.0
Absolute magnitude: 2.5 – 1
Designations: Saturn Nebula, NGC 7009, Caldwell 55

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