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NGC 7293 - the Helix- or Sunflower Nebula in the constellation Aquarius

Object description:

NGC 7293 - the Helix Nebula in the constellation Aquarius - is with a distance of nearly 650 light-years the closest to the Sun and one of the largest planetary nebulae in our Milky Way (and according to the image authors also one of the most beautiful). The nebular envelope was blown off into space about 11 000 years ago by the central star in the final phase of its stellar life. Today the remains of the star - CSI-21-22270 - can be seen as an extremely blue white dwarf star in the center of the nebula, which stimulates the gas masses to glow by its very strong UV radiation. The surface temperature of the central star is more than 100 000 Kelvin. The nebular envelope expands at about 20 kilometers per second.

The diameter of the brightest part of the Helix nebula is about 3.5 light-years, corresponding to an apparent half moon diameter. The highest excitation state is inside, where a strong blue-green color is present. Here dominates by far the strongest emission of the Helix Nebula, that of the doubly ionized oxygen of the O-III line.

The Helix Nebula gives us an idea how the life of our sun will end in three, four billion years. NGC 7293 discovered in 1823 by the German astronomer Karl Ludwig Harding. An amazing collection of images in special spectral regions of the Helix Nebula can be found at this URL

« Click here or the thumbnail to load a large annoted image and a size comparison to the full moon.
The comparison below shows to scale the apparent sizes of the planetary nebulae, left: NGC 7293 (12.8 arcminutes), center: Messier 27 (5.8 arcminutes) and right: IC 5148 (2.0 arcminutes). Total exposure time NGC 7293: 240 min, Messier 27: 130 min and IC 5148: 180 min.

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