Space is filled with clouds of gas and dust called nebulae. In an emission nebula such
as the Orion Nebula Mosaic (at left), the gas visibly
glows because of hot nearby stars. Dark nebulae, such as Horsehead in Orions belt,
appear as shadows against a glowing area. Reflection nebulae mirror the light their gas
clouds catch from nearby stars.
Observations with the space telescope confirm that the Orion
Nebula Mosaic contains circumstellar disks, thought by some astronomers to be planet-forming regions.
The Hubble Space Telescope has expanded astronomical knowledge into the farthest
regions of the universenearly to the earliest moments of time. It has confirmed
the existence of thousands of remote galaxies and of black holes. Closer to home, it
has given us our first good look at the planet Pluto.