December 16, 2004: Looks can be deceiving, especially when it comes to celestial objects like galaxies and nebulas. These objects are so far away that astronomers cannot see their three-dimensional structure. The Helix Nebula, for WATCH: HubbleMinute Video HubbleMinute - Helix Nebula: A New Twist example, resembles a doughnut in colorful images. Earlier images of this complex object -- the gaseous envelope ejected by a dying, sun-like star -- did not allow astronomers to precisely interpret its structure. One possible interpretation was that the Helix's form resembled a snake-like coil. Now, a team of astronomers using NASA's Hubble Space Telescope has established that the Helix's structure is even more perplexing. Their evidence suggests that the Helix consists of two disks nearly perpendicular to each other.See the rest:
A planetary nebula is the glowing gaseous envelope expelled from a dying, sun-like star. Planetary Nebulas come in a variety of shapes, from rings to elegant goblets. Their complex structures yield clues about the final days of a star's life. These glowing gas clouds were named by stargazers who thought the objects looked like the disks of planets when viewed through small telescopes.
The Sun will create a similar glowing cloud of expelled material, but astronomers do not expect it to have such a complex structure as the Helix. The Helix's intricate structure may have been formed by a pair of stars.
Astronomers are trying to understand the evolution and fate of stars like our Sun. The planetary nebula stage is the last phase in the life of an aging, sun-like star. The glowing clouds of gas that make up a planetary nebula are forensic evidence, yielding information on the type of star or stars that made them.
Images provide a two-dimensional view of an object. A picture of a tree, for example, shows the leaves, branches, and trunk. If we wanted to know more about the tree than what is shown in the picture, we could find the tree, walk around it, and study it. We cannot do that with objects in space. Astronomers must rely on observatories like the Hubble Space Telescope to take images of the objects. But the telescope only sees the part of an object that faces Earth. That is why astronomers need other diagnostic information, such as measurements of the speed of the gas within the object, to understand its true structure.