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Astronomical Observatory: Cool Images

Astr111 Photography Projects, Fall 2004

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The Helix Nebula, Sharon Abraham

Helix Nebula Photograph

There are about 1500 nebula in the Milky Way and a new one is created almost every year. A nebula is a cloud of interstellar gas or dust ejected by a giant star late in its life. A star becomes a red giant when it has burnt away its entire hydrogen core through fission producing carbon and oxygen. The burning hydrogen forms a thin outer shell. The fission process continues until the core runs out of energy or contains iron. Planetary nebulae are illuminated by their central bright star.

The Helix nebula was discovered by Karl Ludwig Harding before 1824. It is at a distance of about 450 light years and is one of the closest planetary nebula. Even though it is one of the largest nebulae known it is difficult to observe visually. It covers an area of 16 arc min in diameter or 1.5 light years.

Looking at the image produced background stars can be seen through the rings of the nebula. For this reason we can identify them to be diffuse rings comprised of optically thin gases. The outer rings of the nebula are predominantly red indicating that it is comprised of hydrogen atoms. The next layer is yellow which could indicate that it is made of nitrogen and finally the inner layer is faintly green hence is comprised of oxygen atoms. These atoms are excited by the central star's ultraviolet radiation. The distinct layers lead us to believe that the original star shed these layers in sequence as the core atomically transformed. In the center of the nebula a small white star can be seen. This is the white dwarf star that produced the helix. The absence of interstellar gas between the nebula and the star shows that the star has stopped emitting atoms and must be at a stable equilibrium. The last gases to be released were carbon so the star has a carbon core and does not have enough pressure or energy to produce further atomic fusion. The distance between the star and the helix is large is evidence that it a relatively old nebula. The star continues to glow due to stored thermal energy. To the right of the nebula there is a bright star with a tail pointing down. This is unusual but upon closer examination it can be deduced that this is a product of saturation or over exposure. The nature of the tail is a result of the telescope used and its fundamental characteristics.


Voyages by Fraknoi, Morrison, and Wolff.

Special Thanks to Chris, the lab assistant.






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