Sky Object of the Month – September 2017

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Sky Object of the Month – September 2017

(Courtesy LVAS Observer’s Challenge*)

NGC 6905 – Planetary Nebula in Delphinus (Mag. 11.1; Size 42” X 35”)

                 This month’s LVAS Observer’s Challenge takes us to the northwest corner of Delphinus and the 11th magnitude planetary NGC 6905, also known as the Blue Flash Nebula. The challenge begins right away when you try to find NGC 6905. At the 2000 coordinates RA: 20h22m23.0s Dec: +20°06’16”, it’s positioned in a star-rich part of the Milky Way, but away from any nearby bright stars. The best route for star-hoppers might be a 4 degree trip eastward from 5th magnitude eta (η) Sagittae (see charts below). In his book Cosmic Challenge, author Phil Harrington offers an interesting way to locate NGC 6905 without resorting to star-hopping or using GoTo technology. Simply center eta Sge in a low power eyepiece and wait 16 minutes. Earth’s 4 degree rotation during that time will bring NGC 6905 into view.                  The next challenge is in determining the smallest aperture that will pick up NGC 6905. It has reportedly been seen with a 4-inch scope, bit its low surface brightness mandates dark skies. Larger instruments will reveal a north-south elongation. Can you detect its bluish color (not as obvious as the nick-name might imply) and glimpse its 14th magnitude central star?

NGC 6905 was discovered by William Herschel in 1784, hence its designation H.IV 64 or 164   (signifying the 16th entry in Class 4 [Planetary Nebulae] of his deep sky catalog) on older star atlases. Its distance uncertain, but may be in excess of 4000 light years.

                                                                                                                                    Glenn Chaple for the LVAS




Chart adapted from Cosmic Challenge by Phil Harrington.





*The purpose of the LVAS Observer’s Challenge is to encourage the pursuit of visual observing.  It is open to everyone that is interested, and if you are able to contribute notes, drawings, or photographs, the LVAS will be happy to include them in our monthly summary.  If you would like to contribute material, submit your observing notes, sketches, and/or images to either Roger Ivester ( or Fred Rayworth ( To find out more about the LVAS Observer’s Challenge or access past reports, log on to

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