The background image(stars9.jpg) is from a site called Jerry's Universe.Although there is no explicit copyright notice ,the text on the page suggests that it's free to use:"Now journey through the galaxies. and create your free E-mail and web page backgrounds. Blast off and have fun!"
The image used for the list style markers(stea.png) is in the public domain and can be found here.
The pictures in the image gallery have been created by NASA,and are therefore in the public domain,according to NASA's copyright policy.
The articles have used information from the following sources:
