Description:
The Ring Nebula (M 57, NGC 6720) is a planetary nebula in the northern constellation of Lyra. Such a nebula is formed when a star, during the last stages of its evolution before becoming a white dwarf, expels a vast luminous envelope of ionized gas into the surrounding interstellar space. It is located in thge constellation of Lyra, about 2,567 light years from earth with an apparent magnitude of 8.8. It has an angular size of 1.5 x 1 arc-minutes, representing 1.3 light years.
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. In the outer region of the ring, part of the reddish hue is caused by hydrogen emission at 656.3 nm. Overall, the observed nebulosity has been currently estimated to be expanding for approximately 1,610 ± 240 years.
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