Saturn Nebula

Lore & Background

The Saturn Nebula was discovered by William Herschel on September 7, 1782, using a telescope of his own design in the garden at his home in Datchet, England, and was one of his earliest discoveries in his sky survey. It was originally a low-mass star that ejected its layers into space, forming the nebula. The central star is now a bright white dwarf star of apparent magnitude 11.5. The nebula gets its name from its superficial resemblance to the planet Saturn with its rings nearly edge-on to the observer, and was so named by Lord Rosse 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 6543 and NGC 2371-2.

The distance of the Saturn Nebula is not known precisely. Sabbadin et al. 2004 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 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.

Reader's Guide

The Saturn Nebula holds significance as one of the earliest discoveries in William Herschel's sky survey, made in 1782 with a telescope of his own design. Its naming by Lord Rosse in the 1840s reflects the historical improvement in telescope resolution that allowed its Saturn-like shape to be recognized. The nebula is notable for its complex morphology, including ansae that are also visible in other planetary nebulae such as NGC 3242, NGC 6543, and NGC 2371-2. Its distance remains uncertain, with two estimates given: 5,200 light-years (Sabbadin et al. 2004) and 3,900 light-years (O'Dell 1963). The central star's strong ultraviolet irradiation produces the nebula's characteristic fluorescent green tint via doubly ionized oxygen. The object is included on many 'best of' observing lists, and its visual magnitude of 8 makes it accessible to amateur telescopes, where it appears as a greenish-yellowish hue. Its radial velocity of 28 miles per second towards Earth and its location 1 degree west of Nu Aquarii provide practical reference for observers.

Did You Know?

• It was named by Lord Rosse in the 1840s for its resemblance to Saturn with rings nearly edge-on.
• The central star has a temperature of 55,000 K and a visual magnitude of 11.5.