AstroTRENDS shows how popular specific astronomic topics are in the literature throughout the years. For instance, you could track the popularity of Dark Energy vs. Dark Matter; or the rise of exoplanetary-themed papers since the discovery of the first exoplanets in 1992. As an example, check out this post I wrote about whether the astronomical community has settled on the “extrasolar planet” or “exoplanet” monicker.
You can normalize keywords with respect to one another, or the total article count, to track relative trends in popularity (say, the growth of “Transits” papers compared to “Radial Velocity” papers). Finally, you can click on a specific point to see all the papers containing the keyword from that year (maybe that spike in a keyword is connected to a discovery, a new theory or the launch of a satellite?).
How does it work? I crawled ADS for a small number of keywords that I thought were interesting (but you can ask me for more!), and counted how many refereed articles were published containing that keyword in the abstract for each year between 1970 and 2013. Keywords containing multiple words are contained within quotes, to specify that all words must be in the abstract.
Play and have fun with it, and if you find an interesting trend, you can share it with others by copying and pasting the address from the “Share” box. (Feel free to send it to me, too!)