(4) NASA.
http://en.wikipedia.org/wiki/Image:Sirius_A_and_B_Hubble_photo.jpg.
Public Domain.
(5) http://en.wikipedia.org/wiki/Image:Pleiades_large.jpg. GNU-FDL.
(6) http://en.wikipedia.org/wiki/Image:
Morgan-Keenan_spectral_classification.png. GNU- FDL.
(7) NASA.http://en.wikipedia.org/wiki/Image:
Abell_S740%2C_cropped_to_ESO_325-G004.jpg. Public Domain.
(8) NASA.http://en.wikipedia.org/wiki/File:
A_Swarm_of_Ancient_Stars_-_GPN-2000-000930.jpg. Public Domain.
(9) http://hubblesite.org/newscenter/archive/releases/2005/11/image/a. Public
Domain.
(10) NASA/JPL-Caltech/R.Hurt, Spitzer Science Center.
http://www.spitzer.caltech.edu/Media/mediaimages/sig/sig05-010.shtml.
Public Domain.
(11) NASA.http://quest.arc.nasa.gov/hst/about/edwin.html. Public Domain.
(12) Harold T. Stokes, Ian Tresman, Georg Wiora.
http://en.wikipedia.org/wiki/Image:Redshift.png. CC-BY-SA and GNU-FDL.
(13) http://en.wikipedia.org/wiki/Image:Orion1%7E.jpg. CC-BY-SA.
(14) NASA.
http://en.wikipedia.org/wiki/Image:M101_hires_STScI-PRC2006-10a.jpg.
Public Domain.
(15) http://hubblesite.org/newscenter/archive/releases/2005/09/image/a/.
Public Domain.
(16) NASA.http://en.wikipedia.org/wiki/Image:Eagle_nebula_pillars.jpg.
Public Domain.
(17) http://en.wikipedia.org/wiki/Image:Universe_expansion2.png. Public
Domain.
(18) http://hubblesite.org/newscenter/archive/releases/1999/19/image/i. Public
Domain.
(19) http://en.wikipedia.org/wiki/Image:Milky_Way_from_Flickr.jpg. CC-BY-SA.