Here's web links for each of the story topics, along with a brief description of what's found there.

1. Mysteries of the Sun

Tour of the Sun (Has different levels for different age groups.)
Bumps on the Sun (Explains bumps on Sun.)

2. Saturn's rings

Mission to Saturn home page
Tour of Saturn - (Beginner, intermediate and advanced levels for different age groups.)
Overview of Saturn - (Teachers; older students. Lots of good links.)

3. Comets & shooting stars

Stardust home page
Shooting stars - (Info about shooting stars.)
Comets- (Info about comets.)

4. Mars life

Mars Tour
Life underground - (Good article. Grades 6-12.)
Ancient bacteria - (Fun article grades 6-12. Also has more links.)

5. Why the Earth turns

NASA answers - (Good NASA article. Grades 4-12.)
Origin of the Moon - (Great graphics for all ages. Good overview for grades 6-12.)
Research continues - (Highlights role of women in this science research. Article grades 8-12.)

6. Mission to Titan

Titan mission home page
We're going to Titan! - (Fun NASA site on Cassini mission.)
A look at Titan - (Info on Titan.)

7. Galaxies

Discovering galaxies - (Can adjust level for different age groups. Excellent site.)
Galaxy activities - (K-8; uses activities to explore galaxies.)
Who was Hubble? - (Picture and short bio of Edwin Hubble.)

8. Colliding galaxies

Are we going to crash? - (Grade 6-12. Story and pictures describe possible collision in store for our own galaxy.)
Great collision - (Grade 6-12. Great picture of colliding galaxies. Links.)

9. Black holes

Discovering black holes - (Can adjust level for different age groups.)
What's a black hole? - (Good Q & A about black holes for older students.)

10. Double stars

Planets around double stars - (Info on planet-formation around double stars.)
Binary Stars-(Info on binary stars.)

11. Pulsars

Discovering pulsars - (Info on pulsars. Links.)
Listen to a pulsar! - (Scroll down to "Pulsar Sounds" and click one of the buttons. Highly recommended.)

12. Space Shuttle

How the Shuttle works - (Commercial site, but very good.)
Shuttle launch site - (NASA home page for Shuttle info.)

13. Hubble Space Telescope

Who was Hubble? - (Picture and short bio of Edwin Hubble.)
Explore the Space Telescope - (Can adjust level for different age groups. Great site. Links.)

14. Space travel

Warp drive when? - (Great NASA site. Full of resources. Grades 6-12.)

15. Space Station

News from the Space Station - (Start page for Space Station info. Lots of links.)

16. Time machines

Looking back in time - (Explains "light year." Grades 4-12.)

17. Big Bang Theory

History of the Big Bang - (All age groups. Can change "level" for different age groups.)

18. Star dust

Stars and star dust
Star people

19. Dark matter

What is dark matter? - (For grade 6-12)
Exploring dark matter - (Can adjust for different age groups, K-12.)

20. Alien life

Discovering new planets - ("PlanetQuest:" Good site dedicated to new planet discoveries.)
Looking for alien life - (Good start page about the search for intelligent life. Includes link to popular software that allows your own computer to join the search for "E.T.")