This is an image of Messier 57 nebula obtained using frames captured in the night from 16 to 17 of June 2016 with Canon EOS 600D + Canon EF-S F/4-5.6 55-250mm IS II lens (@ 250mm; F/7) fixed at EQ5 motorized mount.
The nebula is a remnant of a star, which ended active life and expelled its outer layers. A core of the dead star -- a white dwarf -- could be hardly distinguished in the center of the nebula.
Greenish color of the nebula is caused by double-ionized oxygen; a reddish color of outer layers corresponds to hydrogen and ionized nitrogen. A density of glowing gas is very small yet many times denser than interstellar medium.
Estimated size of the nebula is about a light-year, a distance to it is ~2300 light-years.
The previous image was made using DeepSkyStacker: good yet not perfect program. This picture (which is definitely more realistic) is a result of stacking of 40 frames (30s exposure each) using FITStacker program. Images were calibrated and aligned using IRIS (15 offsets, 15 darks, and 15 flats were used for calibration).
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