NGC 6369 : Little Ghost Nebula

The planetary nebula NGC 6369 is known to amateur astronomers as the "Little Ghost Nebula," because it appears as a small, ghostly cloud surrounding the faint, dying central star. Astronomers call such an object a planetary nebula, because its round shape resembles that of a planet when viewed with a small telescope. The remnant stellar core in the center is now sending out a flood of ultraviolet (UV) light into the surrounding gas causing ioniza- tion. The doughnut-shaped blue-green ring represents light from ionized oxygen atoms that have lost two electrons (blue) and from hydrogen atoms that have lost their single electrons (green). Red marks emission from nitrogen atoms that have lost only one electron.

IC 4406 : Retina Nebula

Like many other  planetary nebulae, IC 4406 exhibits a high degree of symmetry as gas and dust form a vast donut of material streaming outward from the dying star; from Earth, we are viewing the donut from the side. The donut of material confi- nes the intense radiation coming from the remnant of the dying star. Gas on the inside of the donut is ionized by light from the central star and glows. Light from oxygen atoms is rendered blue in this image; hydrogen is shown as green, and nitrogen as red. One of the most interes- ting features of IC 4406 is the irregular lattice of dark lanes that kriss-cross the center of the nebula.  The lanes have a density of dust and gas that is a thousand times higher than the rest of the nebula.