Planetary Nebulae – 26th June 2003

This month’s talk, about Planetary Nebulae was given by Owen Brazell. He started by telling us about the early observations of planetary nebulae by observers like Messier, Ross, and the Herschels. William Herschel first used the description “planetary nebula“. Many catalogues of diffuse objects, beginning with those by Messier and Herschel, have included planetary nebulae, but only recently have attempts been made to produce catalogues exclusively of planetary nebulae. In part this has been because it has been difficult to identify them positively. Early spectroscopic observations discovered that their spectra included emission lines which were later shown to be caused by “forbidden” ionisation states of oxygen. However, other objects also show similar spectra. Early catalogues often included objects like supernova remnants which are in some respects similar. While showing us images of planetary nebulae taken by the Hubble Space Telescope and other observatories, Owen explained the current theories as to how planetary nebulae are formed. The variety of forms shown in the images helped underline the uncertainties in the current theories, and there is clearly still much to be learned about these fascinating objects. The following links might be useful for anyone interested in learning more.

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