AAO image reference AAT 15. « Previous || Next »
Top left is NE. Image width is about 25 arc min
Image and text © 1990-2010, Australian Astronomical Observatory, photograph by David Malin.
This faint object is the nearest planetary nebula to the Sun and on deep photographs has a diameter of about half a degree -- the same apparent size as the Sun in the sky. Planetary nebulae are the ejected surface layers of a dying star, and advertise an end point in the evolution of stars around the mass of the Sun. The AAT colour picture shows the brighter parts of the nebula, revealing various ionisation levels within the shell of matter ejected from the central star. The greenish middle portion is evidence of excited oxygen atoms, while the outer red is predominantly light from nitrogen and hydrogen. The smallest of the radial blobs inside the red shell are about 150 astronomical units across (150 times the Earth-Sun distance) and they give this beautiful object its alternative name, the Sunflower Nebula. These fine features are emphasised here by using an unsharp mask during the copying stage of the original plates. The Helix is about 700 light years away in Aquarius, and is almost 200 times more distant than the nearest stars.
AAT 15a. The Helix nebula, no unsharp mask, wide field
AAT 15b. The Helix nebula, wide field, deep image
AAT 15c. The Helix nebula, unsharp mask, same scale as image above
Constellation of Aquarius (external site)
For details of photographic exposure, search technical table by AAT reference number.
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