A nebula from Latin: "cloud"is an interstellar cloud of dust, hydrogen, helium and other ionized gases. Originally, nebula was a name for any diffuse astronomical object, including galaxies beyond the Milky Way.
Andromeda Galaxy A massive spiral million light-years away, over twice the diameter of our own Milky Way, it's the largest nearby galaxy. Andromeda's population of bright young blue stars lie along its sweeping spiral arms. by Spitzer Space Telescope
“ This is a deep image of the Sword of Orion - the three stars that make up the weapon hanging off the belt of this famous celestial hunter. The image showcases the amazing mix of physical and optical.
The Hubble Space Telescope took a picture of the planetary nebula PK also known as ESO or Hen and commonly called Menzel 2 (Mz because it was discovered by the astronomer Donald Menzel in Read the details in the article!
This is a composite image of the brightest supernova remnant in optical light in the Large Magellanic Cloud. The Chandra X-ray image (blue) shows million-degree gas in the center. Much cooler gas at the outer parts of the remnant is seen in.