The Encyclopedia of Science Fiction
I don’t remember how I stumbled upon The Encyclopedia of Science Fiction, but it really is a must-see for any ardent fan of science fiction.
The encyclopedia is free, and offers information that covers just about anything you can imagine. It has search function which cover themes, media, and culture, as well as authors and more. I think the theme and culture search functions are especially useful. For example, this entry on Hard Science Fiction, while not expansive, does provide many interesting and relevant facts.
I think that this website goes well with another, The Internet Speculative Fiction Database. This database is useful for looking up specific issues of old and new science fiction magazines, among other things. It has been an invaluable tool for my work coding magazine covers for the Genre Evolution Project. One of my favorites is from an issue of Amazing Stories dated July, 1942. The cover story is called “Blitzkrieg in the Past” and show a T-Rex attacking a German tank.
This also highlights another useful function of the ISFDB. When you peruse the catalog and examine the different years, you can see how historical events impact how science fiction developed. The World War 2 years, in particular, had a profound impact on the type of science fiction that was published, as well as the art.
I hope you enjoy these two wonderful resources as much as I have. I really do believe that they’re invaluable.