(General) Science and Skepticism

• HardScience.info A collection of useful hard science and mathematics links.
• scienceworld.wolfram.com. A huge web ressource on mathematics, physics, chemistry, and astronomy.
• Phil Plait's BadAstronomy.com (about astronomical misconceptions in the media)
• The James Randi Educational Foundation will pay you US$ 1,000,000 if you can do anything paranormal. A hugely enjoyable read, with a weekly column on skepticism.
• Cecil Adam's legendary column on The Straight Dope
• Snopes.com Urban Legends Reference Pages. The definitive Internet reference source for urban legends, folklore, myths, rumors, and misinformation.
• "Number Watch - the guide to wrong numbers in science, media and politics" bravely fights mis-uses and misunderstandings of statistics whenever they are made (i.e., almost all the time).
• Time Travel and Modern Physics. An interesting and very readable essay from the Stanford Encyclopedia of Philosophy.
• In his excellent article "A Physical Description of Flight", David Anderson explains why airplanes really fly.
• The Coming Technological Singularity. An speculative essay on the post-human era by Vernor Vinge.

Science (work-related)

• TP4, my astrophysical alma mater
• SolarWind@TP4 document repository. Talks, schedules, movies relating to the Solar Wind group at TP4.
• Planetary Plasmas Group at MPS
• The Aurolab plasma laboratory of Tromsø

Friends

• Home page of Andreas Müller. What you had always wanted to know about ray tracing, black holes, and astrophysics in general, presented in a very readable fashion.
• Home page of Olaf Eichler. SciFi artwork, Descent II, amateur radio, and tons of weird links.
• My valued colleague Ralf Kissmann launches experimental H₂O-propelled rockets, and reports on impressive achievements on his water rocket page (in German, but with movies!). And speaking of cool rocket projects, watch how John Carmack's ArmadilloAerospace team reaches for the X-prize!

Charities that deserve your support

• Use Ecosia to search the web, and help to protect the rainforest at no costs to you!
• A click a day on the green button at The Rainforest site preserves about one square meter of rainforest, also for free!
• TARGET e.V. fights for the abolishment of women's genital mutilation in several Islamic countries, and successfully so! Founded and run by the godfather of outdoor survival, Rüdiger "Sir Vival" Nehberg.

Misc

• Look at these stunning results of a recent experiment regarding the effect of diet coke on organic tissue!
• My old homepage at RUB. [Mostly in German]
• The world-famous Internet Movie Database.
• Project Gutenberg: Really cheap (e)books!
• You think Daylight Saving Time ("Sommerzeit" in German) is a good idea? Wrong. To see why, go to Initiative Sonnenzeit and find out how you can help to eventually abolish it. [In German]
• To see if you really need to forward that email to all your friends, first check out Frank Ziemann's Hoax-Info Service at TU Berlin. [In German]