Here are some stellar links to the night sky;
www.astronomy-for-kids-online.com - a multitude of links for research and fun related to our universe
http://astronomylinks.com/- over 1,000 astronomy related links categorized by topics. Check out the astronomy jokes links.
www.SkyandTelescope.com/IYA2009 - site for a popular astronomy magazine. Many interesting articles can be accessed from here, but concepts and language some may be a little too mature for many 4th graders. You may need parental help to navigate this site.
http://amnh.com/ology/index.php?channel=astronomy- American Museum of Natural History's site for young people interested in the universe
Please let me know if you find any other fun sites about the stars and planets.