Ring nebula. Zooming out from the Ring Nebula M57, NGC 6720. This is a planetary nebula lying around 2000 light years from Earth in the constellation Lyra. Planetary nebulae are glowing shells of gas and plasma ejected by medium and low-mass stars at the end of their lives. Helium (blue) fills the central structure of the Ring Nebula. Radiation from the white dwarf star, the white dot in the centre of the ring, causes the helium to glow blue. This gives way to cooler turquoise, orange and red gas at greater distances, with irregular knots of dense gas embedded along the inner rim of the ring. Footage created using data from the Hubble Space Telescope, combined with ground-based observations.