This blog randomly selects from a pool of header images. The images are:
Branches against an Australian sky (my photo). See also this post about Branches.
Radiolarian mineral skeletons, drawn by Ernst Haeckel (adapted from here).
An X-ray image of a solar flare. See this post about the image.
Venus by radar light. See this post about the image.
A Widmanstätten pattern (my photo). See this post about the NMNH.
Update: Echinoderms (my photo). See this post about the Australian Museum.
Update: Sun dogs (photo from here). See this post about the phenomenon.
Update: Solar cars in the 2005 North American Solar Challenge, near Winnipeg in Canada (photo from here). See my coverage of the World Solar Challenge and the Abu Dhabi Solar Challenge.
Update: The Aurora Borealis (photo from here). See my aurora-related posts.
Update: An Arabidopsis thaliana flower (photo from here). See my post about the plant.
Update: A selection of milestones in materials technology, simplified from this infographic.
Update: A chemistry laboratory, from a museum in Finland.