w1800 20190827 M57 A7Ra ISO3200 33x30s

M57 is 2,570 light-years from Earth. It has a visual magnitude of 8.8v and photographic magnitude of 9.7p. Photographs taken over a period of 50 years show the rate of nebula expansion is roughly 1 arcsecond per century, which corresponds to spectroscopic observations as 20–30 km s−1. M57 is illuminated by a central white dwarf or planetary nebula nucleus (PNN) of 15.75v visual magnitude.

All the interior parts of this nebula have a blue-green tinge that is caused by the doubly ionized oxygen emission lines at 495.7 and 500.7 nm. These observed so-called "forbidden lines" occur only in conditions of very low density containing a few atoms per cubic centimeter. In the outer region of the ring, part of the reddish hue is caused by hydrogen emission at 656.3 nm, forming part of the Balmer series of lines. Forbidden lines of ionized nitrogen or [N II] contributes to the reddishness at 654.8 and 658.3 nm.

Planetary nebula nucleus (PNN)
Within the last two thousand years, the central star of the Ring Nebula has left the asymptotic giant branch after exhausting its supply of hydrogen fuel. Thus it no longer produces its energy through nuclear fusion and, in evolutionary terms, it is now becoming a compact white dwarf star.
The PNN now consists primarily of carbon and oxygen with a thin outer envelope composed of lighter elements. Its mass is about 0.61–0.62 M, with a surface temperature of 125,000 ± 5,000 K. Currently it is 200 times more luminous than the Sun, but its apparent magnitude is only +15.75, but very brightly visible on my picture.

ObjectM57 or NGC6720 Ring Nebula
Constellation: Lyra
Position: RA 18h 53m 35.079s DEC +33° 01′ 45.03″
Apparent Size: 1.5 x 1.0 arcmin
Apparent Magnitude/surface brightness: +9.4 / +9.3
Distance (average) 2567±115 ly
  
Photo Datas 
Date 27.08.2019, 21:25 UTC
Location Knottenried/Oberallgäu, 1002m ASL
GPS: 47°36’13“ N, 10°11’24“ E
Sky darkness SQM-L Zenit 21.00mag/sqrsec, Object 21.05mag/sqrsec
Ground Temp./Air Pressure 18.5°C /1016mbar
Thermal sky temp./weather  -29.1°C Zenit / high altitude haze
Seeing  4/10 
Telescope TS RC 14" 2845mm f/8.0
Camera Sony A7Ra mod @ T sensor=21.6°C !!
Expose frames ISO 3200, RAW 33x30s, 16 darks
Total expose
16 min. 30s
Filter no
Mount HPS 10Micron GM 3000
Guiding Cam no
Software DSS 3.3.4, Photoshop CC
Remarks  

C 2019 Peter Cerveny