Nebula
A nebula is a giant cloud of gas (mostly hydrogen and helium) and cosmic dust situated between stars in the interstellar medium. Nebulae serve as sites of stellar birth and death—including emission nebulae that glow from ionized gas, reflection nebulae that scatter starlight, and dark nebulae that obscure background stars.
Source: science.nasa.gov
APODs including "Nebula"
Young Moon and Sister Stars
28/04/2007
A young crescent Moon shared the western sky with thin clouds and the sister stars of the Pleiades cluster in this early evening skyscape recorded on April 19th. Astronomical images of the well-known Pleiades often show the star cluster's alluring blue reflection nebulae, but they are washed-out here in the clouds and bright moonlight. While the 3-day old Moon is overexposed, surface features can be seen on the dim lunar night side, illuminated by earthshine - light from sunlit planet Earth. Only a week earlier, brilliant Venus also posed near the sister stars. Of course, Venus has not yet wandered too far from the Pleiades and still rules western skies as the evening star.