Astronomy Picture of the Day is brief and informative. Each image is accompanied by a one-paragraph explanation, with key terms linked to definitions. All past images are held in a searchable archive.

The Hubble Space Telescope's public information office maintains an extensive, constantly updated collection of stunning images and movies from the orbiting observatory; the site also contains press releases and other explanatory texts.

Views of the Solar System delivers what its name promises: a great virtual tour of the sun, planets, satellites, comets and asteroids, including in-depth information about every body mentioned.

Asteroid and Comet Impact Hazards gives the straight facts on what would happen if an asteroid or comet were to strike the earth. There are also pointers to relevant images, scientific findings and policy developments.

Numerical Relativity Exhibitions are maintained by the Relativity Group at the National Center for Supercomputing Applications. The site includes computer graphics and animations that portray the mind-bending world of black holes and Einsteinian relativity.

Virtual Trips to Black Holes and Neutron Stars. Robert Nemiroff of the NASA-Goddard Space Flight Center has created a virtual environment in which the user can witness firsthand the bizarre ways the laws of physics behave around these objects.