APOD 2.8

January 8th, 2011                                          The Helix Nebula

   We have long known about the existence of the Helix Nebula since we learned the constellation Aquarius a few months back, but we never really learned what exactly it was so I figured that this was a fitting APOD choice.  The constellation Aquarius, located approximately 700 light years away, has a sun-like star in its final days. Over the past thousands of years, the star has created NGC 7293, or more commonly known as the Helix Nebula, discovered by Karl Harding in 1824.  This is a typical example of a Planetary Nebula, or an Emission Nebula consisting an expanding glowing shell of ionized gas that is expelled during the final stages of a star's lifespan known as the asymptotic giant branch phase.  The picture shown was taken over 10 hours of exposure time.  The brighter blue insides spans up to 3 light years, but the outer halos give the Nebula a total span of over 6 light years across. The white dot in the center of the Nebula is the sun-like star that allows for all of this to occur.  Recently, much has been learned about the complex geometry of these types of Nebulae but there is no doubt that there is much more to learn about the matter.