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NGC 6369 - the little ghost nebula

Object description:

NGC 6369 is a small and faint planetary nebula with an apparent diameter of only 30 arcseconds in the constellation of Ophiuchus. The central star has the catalogue number HD 158269. NGC 6369 was discovered on 21 May 1784 by the German astronomer Friedrich Wilhelm Herschel.

As is the case with many planetary nebulae, its distance is known with a large uncertainty, the distances vary between 2000 and 5000 light years. Thus the true diameter would be in the range between 0.3 and 1 light year.

The seeing reached values between 1.3'' and 1.9'' in the sum images. The almost full moon was in the sky simultaneously with NGC 6369. Due to the brightened sky, it was very difficult to work out the weak signal of the planetary nebula from the background.

« The picture on the left shows a size comparison to the full moon. Click here or the preview image for loading a largeversion.
HD 158269 is a dying star at the end of its life. A long time ago, it expanded into a red giant star and ejected a large part of its mass into the surrounding space. The gas masses move at a speed of about 24 kilometres per second.
The excavated core area of the star (clearly visible in our picture) is a so called white dwarf and shines strongly at ultraviolet wavelengths. This high-energy UV radiation ionizes oxygen, hydrogen and nitrogen atoms and makes them glow in blue, green and red colors.

Viewed from Earth, NGC 6369 lies behind the dark cloud LDN 73, which is why the foreground stars in our image are all displayed in reddish color.

In a period of about 10,000 years NGC 6369 will disappear into interstellar space, leaving only the white dwarf star. A fate which also our Sun will suffer in about 5 billion years.

The Hubble space telescope photographed NGC 6369 in February 2002 with the wide-angle planetary camera 2. The image shows remarkable details of the ejection process of the gas masses, which are not visible with ground-based telescopes. A large version of the Hubble image can be found here.

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