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Popular Astronomy

July 2016

Three section members sent in five images this month, all credit to them;  apart from the lack of hours of astronomical darkness, bad weather has limited the opportunites for making observations.

David Davies, imaging from Cambridge, sent in this very detailed image of the ''triffid'' emission nebula, M20, in the constellation of Sagittarius.  David used an 8'' Richey Chretien f8 telescope and a QSI583 camera plus Astrodon red, green and blue filters. 

Three dark lanes of dust within the red HII emitting region (656.3 nm) give this emission nebula its popular name;  blue reflection nebulosity is present too in long exposure colour images such as this.  Bok globules are present in M20, indicating stars in the process of formation from dust and gas.

                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                          

Ian Papworth, SPA Membership Secretary, imaged M27, the ''dumbbell'' planetary nebula, in the constellation of Vulpecula.  At the end of their lives,  after the red giant phase, stars similar to our sun eject expanding shells of ionised gas.  The light from planetary nebulae also show emission lines but typically at a wavelenth of 550.7 nm, indicating doubly ionized oxygen  (OIII) at extremely low density.  This property is exploited by visual observers in particular when they use an OIII filter to make a planetary nebula stand out from the background stars.

Ian used a Celestron Nexstar 6SE f6.3 Schmidt Cassegrain telescope and ZWO ASI 120MM mono camera and red, blue and green filters.

                                                                                                                                                                   

Steve Norrie captured these images right at the end of the month with his ES127 APO CF f6 refractor and an Atik 490EX one shot (i.e. colour) camera.  From below left, clockwise, is M27, M52 open cluster in the constellation of Cassiopeia, and M57, the ''ring'' planetary nebula in Lyra.

      

                                                                                                                                                                        

It is interesting to compare the two M27 images, taken with very different equipment.

Steve's image of M57 shows how small it is compared to M27, at around 70 arcseconds across.  The central star of M57 is of magnitude 15.3 and visual observers may not see it even with large telescopes.  M57 is estimated to be around 6,000 years old and is about 2,300 light years from us.  M27 is closer by about 1000 light years, but 4,000 years older.

                                                        

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