This image from the NASA Hubble Space Telescope shows planetary nebula Hen 3-1333. Planetary nebulae have nothing to do with planets - they actually represent the death throes of mid-sized stars like the sun. As they puff out their outer layers, large, irregular globes of glowing gas expand around them, which appeared planet-like through the small telescopes that were used by their first discoverers. The star at the heart of Hen 3-1333 is thought to have a mass of around 60% that of the sun, but unlike the sun, its apparent brightness varies substantially over time. Astronomers believe this variability is caused by a disc of dust which lies almost edge-on when viewed from Earth, which periodically obscures the star.
