Image: A chameleon sky
The sands of time are running out for the central star of this the Hourglass Nebula.
With its nuclear fuel exhausted, this brief, spectacular, closing phase of a sun-like star's life occurs as its outer layers are ejected and its core becomes a cooling, fading white dwarf.
In 1995, astronomers used the Hubble Space Telescope to make a series of images of planetary nebulae, including the one above. Here, delicate rings of colorful glowing gas (nitrogen-red, hydrogen-green, and oxygen-blue) outline the tenuous walls of the 'hourglass.'
The unprecedented sharpness of Hubble's images revealed surprising details of the nebula ejection process and may resolve the outstanding mystery of the variety of complex shapes and symmetries of planetary nebulae.