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NGC 246 - Planetary nebula in the constellation Cetus


Description of object:

The planetary nebula NGC 246 in the constellation Cetus (the whale) was discovered by Wilhelm Herschel on 27 November 1785. The distance of the nebula could be determined with a high precisiony for this type of object. The values are between 1540 and 1860 lightyears. The apparent diameter in the sky is about 3.9 arcminutes, corresponding to an absolute diameter of 1.9 lightyears. The age of NGC 246 was determined to 6600 years. The western edge of the planetary nebula (to the right in the image) is much brighter than the eastern edge. This effect is caused by the combination of the expansion of the nebula and its proper motion through the interstellar medium. The deceleration of the material of the nebula, which is somewhat stronger in the direction of movement, leads to a higher gas density and thus to a more intensive luminescence than on the opposite side of the nebula.

The central star system consists of the 130,000-degree hot blueish white dwarf and a yellowish secondary star with a spectral class K. The secondary is located 3.8 arcseconds next to the white dwarf and can also be seen in the image. The two stars outshine a further dwarf star of the spectral class M with around 0.1 solar masses, which is only in a distance of 1 arc second from the white dwarf and was discovered in 2014.

Also note the numerous very distant, yellowish background galaxies in the image.

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