NGC 6818 is in the constellation Sagittarius at a distance of about 6000 light-years. It has a diameter of about 0.5 light-year. The Hubble telescope observation was taken March 10, 1997 by the Wide Field and Planetary Camera 2. This is a composite of images taken in 3 filters: Halpha is red, Hbeta is blue, and [O III] (doubly ionized oxygen) 5007 is green. As a result of the longer exposure time at Hbeta, the central star of the planetary nebula appears blue. We see a roughly spherical outer envelope as well as a brighter vase-shaped interior "bubble". Astronomers believe that a fast wind from the hot central star is creating the elongated shape and in fact has caused a "blowout" at the two ends of the major axis (lower right and upper left). This nebula looks like a twin of NGC 3918, another planetary nebula (PN) that has been imaged by the Hubble telescope. The structure of NGC 3918 is remarkably similar to that of NGC 6818 - it has an outer spherical envelope, an inner brighter elongated bubble, and it also shows a blowout orifice at one end of the major axis in the bottom right-hand corner. By finding and studying such similar objects, it is hoped that crucial details can be learned about the evolutionary life history of planetary nebulae. One could call this "comparative PNology".
Credits
Credits: Robert Rubin (NASA Ames Research Center), Reginald Dufour and Matt Browning (Rice University), Patrick Harrington (University of Maryland), and NASA| About The Object | |
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| Object Name | NGC 6818 |
| About The Object | |
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| Object Name | A name or catalog number that astronomers use to identify an astronomical object. |
| Object Description | The type of astronomical object. |
| R.A. Position | Right ascension – analogous to longitude – is one component of an object's position. |
| Dec. Position | Declination – analogous to latitude – is one component of an object's position. |
| Constellation | One of 88 recognized regions of the celestial sphere in which the object appears. |
| Distance | The physical distance from Earth to the astronomical object. Distances within our solar system are usually measured in Astronomical Units (AU). Distances between stars are usually measured in light-years. Interstellar distances can also be measured in parsecs. |
| Dimensions | The physical size of the object or the apparent angle it subtends on the sky. |
| About The Data | |
| Data Description |
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| Instrument | The science instrument used to produce the data. |
| Exposure Dates | The date(s) that the telescope made its observations and the total exposure time. |
| Filters | The camera filters that were used in the science observations. |
| About The Image | |
| Image Credit | The primary individuals and institutions responsible for the content. |
| Publication Date | The date and time the release content became public. |
| Color Info | A brief description of the methods used to convert telescope data into the color image being presented. |
| Orientation | The rotation of the image on the sky with respect to the north pole of the celestial sphere. |
