OBSERVER’S CHALLENGE* - JULY, 2021
by Glenn Chaple
NGC 6572 – Planetary Nebula in Ophiuchus (Mag: 8.1, Size: 16” X 13”)
The visual observer is all too aware that, with the exception of double stars like gold and yellow Albireo and ruby-red carbon stars like R Leporis, the deep sky is a pretty colorless place. Bright planetary nebulae like this month’s Observer’s Challenge, NGC 6572 in Ophiuchus, are a notable exception.
NGC 6572 was discovered by the Russian-German astronomer Friedrich Georg Wilhelm von Struve in 1825. Struve was in the midst of a survey to catalog double stars when he came upon “a star surrounded by bright green ellipse of fuzzy light.” At the time, astronomers were unaware of the true nature of such a curiosity. Today we know that NGC 6572 is a planetary nebula – an expanding luminous shell of gas ejected by an aging star. It’s relatively young as planetary nebulae go, perhaps no more than 2600 years.
The 2000.0 coordinates for NGC 5672 are: R.A. 18h 12m 06.6s , Dec. +6° 51’ 13”. I star-hopped there by starting at the 5th magnitude star 71 Ophiuchi, the unlabeled star just south of 72 Ophiuchi on Finder Chart A. Finder Chart B shows an 8th magnitude star, SAO 123133 just northwest of 71 Ophiuchi. A line from this star through 71 Ophiuchi and extended 1.3° brought me to a triangle of 8th magnitude stars, NGC 6572 was a little less than a degree SSE of the southernmost star in the triangle.
At 39X in my 10-inch f/5 reflector, NGC 6572 appeared stellar. At 208X, it was definitely non-stellar when compared to a pair of stars immediately to its east, It seemed slightly elongated in a north-south orientation and was decidedly pale blue. I was unable to detect the central star, which is said to be 13th magnitude.
NGC 6572 is approximately 5000 light years away. This translates to an actual diameter of ⅓ light year.
*The purpose of the Observer’s Challenge is to encourage the pursuit of visual observing. It is open to anyone who is interested. If you’d like to contribute notes, drawings, or photographs, we’d be happy to include them in our monthly summary. Submit your observing notes, sketches, and/or images to Roger Ivester (firstname.lastname@example.org). To find out more about the Observer’s Challenge, log on to rogerivester.com/category/observers-challenge-reports-complete,
Finder Charts for NGC 6572
From AAVSO’s Variable Star Plotter (VSP). Annotations by Glenn Chaple. Field 3° by 4°. Stars plotted to 11th magnitude.
Images for NGC 6572
Image by Mario Motta, MD (ATMoB) 32-inch scope. H alpha, O3 , and S2 filters -30 minutes each.
Sketch by Glenn Chaple (ATMoB)